Nacre ( / ˈ n eɪ k ər / NAY -kər , also / ˈ n æ k r ə / NAK -rə ), also known as mother of pearl , is an organic–inorganic composite material produced by some molluscs as an inner shell layer. It is also the material of which pearls are composed. It is strong, resilient, and iridescent .
129-498: Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and reddish pink or blue eyes. Individuals with the condition are referred to as albinos . Varied use and interpretation of the terms mean that written reports of albinistic animals can be difficult to verify. Albinism can reduce the survivability of an animal; for example, it has been suggested that albino alligators have an average survival span of only 24 hours due to
258-476: A buffalo in Jamestown, North Dakota , and inspiration for Herman Melville 's novel Moby-Dick , a sperm whale known as Mocha Dick . The most important pigments that determine plumage colouration in birds are melanines and carotenoids. The latter are ingested in food and transformed into colour pigments by enzymes. Aberrations in this pigmentation are mostly caused by food deficiencies and usually do not have
387-426: A ceramic tile or marble base. The tesserae are hand-placed and closely sandwiched together, creating an irregular mosaic or pattern (such as a weave). The laminated material is typically about 2 millimetres (0.079 in) thick. The tesserae are then lacquered and polished creating a durable and glossy surface. Instead of using a marble or tile base, the nacre tesserae can be glued to fiberglass . The result
516-511: A toque macaque ( M. sinica ), rhesus macaque ( M. mulatta ), and bonnet macaque ( M. radiata ). Albinism was observed in jungle cats ( Felis chaus ) and jackals ( Canis aureus ) along the coastline of the southern Western Ghats (Kerala and Kanyakumari coast, India). Albinism was observed in jungle cats from the Amaravila area of Trivandrum district in the Kerala State. Albinism in jackals
645-527: A "semi-lethal mutation". Pigmentation disorders such as albinism are occasionally associated with hearing impairments in mice, rats, guinea pigs and cats. Intentionally bred albinistic strains of some animal species are commonly used as model organisms in biomedical research and also as pets. Examples include the BALB/c mouse and Wistar and Sprague Dawley rat strains, laboratory rabbits and ferrets. Some researchers have argued that albino animals are not always
774-655: A colour resulting from selective colour absorption . What is perceived as a plant or animal's "colour" is the wavelengths of light that are not absorbed by the pigment, but instead are reflected. Biological pigments include plant pigments and flower pigments . Animals can appear coloured due to two mechanisms, pigments and structural colours . Animals may have both biological pigments and structural colours, for example, some butterflies with white wings. Many animal body-parts, such as skin , eyes , feathers , fur , hair , scales and cuticles, contain pigments in specialized cells called chromatophores . These cells are found in
903-490: A condition called agouti , they make multi-coloured individual hairs. The production of melanin occurs in melanocytes in a complex process involving the enzyme tyrosinase . Mammals have a gene that codes for the presence of tyrosinase in cells – called the TYR gene. If this gene is altered or damaged, melanin cannot be reliably produced and the mammal becomes an albino. Besides the TYR gene, several other genes can cause albinism. This
1032-498: A condition known as albinism . Because melanin is an aggregate of smaller component molecules, there are many different types of melanin with different proportions and bonding patterns of these component molecules. Both pheomelanin and eumelanin are found in human skin and hair, but eumelanin is the most abundant melanin in humans, as well as the form most likely to be deficient in albinism. Melanins have very diverse roles and functions in various organisms. A form of melanin makes up
1161-519: A decrease in the degree of polymerization of ocular melanin has been proposed to turn the normally anti-oxidant polymer into a pro-oxidant . In its pro-oxidant state, melanin has been suggested to be involved in the causation and progression of macular degeneration and melanoma . Rasagiline , an important monotherapy drug in Parkinson's disease, has melanin binding properties, and melanoma tumor reducing properties. Higher eumelanin levels also can be
1290-442: A disadvantage, however, beyond a higher disposition toward vitamin D deficiency. Dark skin is a complicating factor in the laser removal of port-wine stains . Effective in treating white skin, in general, lasers are less successful in removing port-wine stains in people of Asian or African descent. Higher concentrations of melanin in darker-skinned individuals simply diffuse and absorb the laser radiation, inhibiting light absorption by
1419-455: A dominant albinism in the rainbow trout . Albinism occurs throughout the animal kingdom. The condition is most commonly seen in birds, reptiles and amphibians, but more rarely seen in mammals and other taxa. It is often difficult to explain occasional occurrences, especially when only one documented incidence has occurred, such as only one albino gorilla and one albino koala . In mammals, albinism occurs once in every 10,000 births, but in birds,
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#17331159847911548-410: A fungus) melanins appear to play important roles in virulence and pathogenicity by protecting the microbe against immune responses of its host . In invertebrates, a major aspect of the innate immune defense system against invading pathogens involves melanin. Within minutes after infection, the microbe is encapsulated within melanin (melanization), and the generation of free radical byproducts during
1677-530: A fungus, such as Lacazia loboi . Famous albino mammals include Migaloo , a humpback whale living off the coast of Australia; Pinky , a bottlenose dolphin living in and around in Calcasieu Lake , Louisiana; Carolina Snowball, a popular albino bottlenose dolphin displayed at the Miami Seaquarium in the early 1960s; Snowflake , a Barcelona Zoo gorilla , and Mahpiya Ska , ( Sioux for White Cloud),
1806-437: A genetic basis. Well-known examples are flamingos , which owe their distinct pink colour to the presence of red carotenoids in their natural food. When these carotenoids are in short supply, these birds appear white after the next moult . Mutations causing changes in carotenoid-based colour pigments are rare; melanine mutations occur much more frequently. Two types of melanin, eumelanin and phaeomelanin, are present in birds. In
1935-401: A good diagnostic feature with which to distinguish leucistic and albino individuals – the colour of the eye." However, there are multiple forms of albinism – currently seven types recognised for humans – most of which do not result in red or pink pupils. The term "partial albino" is sometimes used in the literature. However, it has been stated that "A common misnomer is 'partial albino' – this
2064-407: A growing L-DOPA core polymer. It is possible to enrich melanin with selenium instead of sulphur . This selenium analogue of pheomelanin has been successfully synthesized through chemical and biosynthetic routes using selenocystine as a feedstock. Due to selenium's higher atomic number, the obtained selenomelanin can be expected to provide better protection against ionising radiation as compared to
2193-624: A lack of protection. Albino humans must use an excessive amount of sunscreen, even if the sun is hidden behind the clouds. Animals with albinism may lack protective camouflage in some environments, and are therefore less able to conceal themselves from their predators or prey. However, in other environments albino animals are less likely to be killed, and selection may favor them. The lower survival rate of animals with albinism in certain environments has been documented, however, it has been stated that in studies where animals had many places to hide, predators captured albino and normally coloured animals at
2322-489: A larger fracture energy than the elastic energy at fracture of the hard phase. Fiber pull-out , which occurs in other ceramic composite materials , contributes to this phenomenon. Unlike in traditional synthetic composites, the aragonite in nacre forms bridges between individual tablets, so the structure is not only held together by the strong adhesion of the ceramic phase to the organic one, but also by these connecting nanoscale features. As plastic deformation starts,
2451-417: A medical condition that they were born with" and "a person or animal with white skin and hair and pink eyes" do not include feathers, scales or cuticles of birds, fish and invertebrates, nor do they include plants. Some definitions are too broad to be of much use, e.g. "an animal or plant with a marked deficiency in pigmentation". Other definitions of albinism encompass most of the major animal taxa, but ignore
2580-403: A natural material. These particles line up in a way that resembles fibers, and they continue to multiply. When there are enough particles, they come together to form early stages of nacre. The growth of nacre is regulated by organic substances that determine how and when the nacre crystals start and develop. Each crystal, which can be thought of as a "brick", is thought to rapidly grow to match
2709-507: A secondary phenomenon induced by adaptation to parasites and tropical diseases. Early humans evolved dark skin color, as an adaptation to a loss of body hair that increased the effects of UV radiation. Before the development of hairlessness, early humans might have had light skin underneath their fur, similar to that found in other primates . Anatomically modern humans evolved in Africa between 200,000 and 100,000 years ago, and then populated
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#17331159847912838-498: A similarly formed but brittle mineral, is the speed at which it grows in a certain direction (roughly perpendicular to the shell). This growth is slow in nacre, but fast in fibrous aragonite. A 2021 paper in Nature Physics examined nacre from Unio pictorum , noting that in each case the initial layers of nacre laid down by the organism contained spiral defects. Defects that spiralled in opposite directions created distortions in
2967-576: A single monomer that accounts for the measured elemental composition and some properties of melanin, but is unlikely to be found in nature. Solano claims that this misleading trend stems from a report of an empirical formula in 1948, but provides no other historical detail. The first step of the biosynthetic pathway for both eumelanins and pheomelanins is catalysed by tyrosinase . Dopaquinone can combine with cysteine by two pathways to benzothiazines and pheomelanins Also, dopaquinone can be converted to leucodopachrome and follow two more pathways to
3096-493: A white beak, white plumage, non-coloured skin, white talons and pink or red eyes. Albinism is only seen in about 1 of every 1,800 birds. The two most common species of albino birds are the common house martin and the American robin . Famous albino birds include " Snowdrop ", a Bristol Zoo penguin . In one study, albinism in birds has been categorised according to the extent of pigment absence. However, it has been argued that
3225-449: A wide range of animals including amphibians , fish , reptiles , crustaceans and cephalopods . Mammals and birds , in contrast, have a class of cells called melanocytes for colouration. The term chromatophore can also refer to coloured, membrane-associated vesicles found in some forms of photosynthetic bacteria . Chromatophores are largely responsible for generating skin and eye colour in poikilothermic animals and are generated in
3354-542: Is Mosse et al. , 2000 on mice but also includes Mosse et al. , 1994, Mosse et al. , 1997, Mosse et al. , 1998, Mosse et al. , 2001, Mosse et al. , 2002, Mosse et al. , 2006, Mosse et al. , 2007 and Mosse et al. , 2008. Melanin produced by plants are sometimes referred to as 'catechol melanins' as they can yield catechol on alkali fusion. It is commonly seen in the enzymatic browning of fruits such as bananas. Chestnut shell melanin can be used as an antioxidant and coloring agent. Biosynthesis involves
3483-457: Is a clearly defined set of seven types of genetic mutations which reduce or completely prevent the synthesis of eumelanin or pheomelanin , resulting in reduced pigmentation. Type I oculocutaneous albinism (OCA1a) is the form most commonly recognised as 'albino' as this results in a complete absence of melanin in the skin, hair/fur/feathers, and pink pupils, however this has led many to assume that all albinos are pure white with pink pupils, which
3612-436: Is a family of biomolecules organized as oligomers or polymers , which among other functions provide the pigments of many organisms . Melanin pigments are produced in a specialized group of cells known as melanocytes . There are five basic types of melanin: eumelanin , pheomelanin , neuromelanin , allomelanin and pyomelanin . Melanin is produced through a multistage chemical process known as melanogenesis , where
3741-652: Is a lightweight material that offers a seamless installation and there is no limit to the sheet size. Nacre sheets may be used on interior floors, exterior and interior walls, countertops, doors and ceilings. Insertion into architectural elements, such as columns or furniture is easily accomplished. Nacre inlay is often used for music keys and other decorative motifs on musical instruments. Many accordion and concertina bodies are completely covered in nacre, and some guitars have fingerboard or headstock inlays made of nacre (or imitation pearloid plastic inlays). The bouzouki and baglamas (Greek plucked string instruments of
3870-435: Is also important in mammalian pigmentation. The coat pattern of mammals is determined by the agouti gene which regulates the distribution of melanin. The mechanisms of the gene have been extensively studied in mice to provide an insight into the diversity of mammalian coat patterns. Melanin in arthropods has been observed to be deposited in layers thus producing a Bragg reflector of alternating refractive index. When
3999-408: Is also negatively impacted by dehydration. Water acts as a plasticizer for the organic matrix, improving its toughness and reducing its shear modulus. Hydrating the protein layer also decreases its Young's modulus , which is expected to improve the fracture energy and strength of a composite with alternating hard and soft layers. The statistical variation of the platelets has a negative effect on
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4128-439: Is also present in the skin, and redheads consequently often have a more pinkish hue to their skin as well. Exposure of the skin to ultraviolet light increases pheomelanin content, as it does for eumelanin; but rather than absorbing light, pheomelanin within the hair and skin reflect yellow to red light, which may increase damage from UV radiation exposure. Pheomelanin production is highly dependent on cysteine availability, which
4257-687: Is an effective melanin bleach. There are approximately nine types of oculocutaneous albinism , which is mostly an autosomal recessive disorder. Certain ethnicities have higher incidences of different forms. For example, the most common type, called oculocutaneous albinism type 2 (OCA2), is especially frequent among people of black African descent and white Europeans. People with OCA2 usually have fair skin, but are often not as pale as OCA1. They (OCA2 or OCA1? see comments in History) have pale blonde to golden, strawberry blonde, or even brown hair, and most commonly blue eyes. 98.7–100% of modern Europeans are carriers of
4386-524: Is as of 2021 developing a product nacre to create "PearlBone", which could be used on patients needing bone grafting and reconstructive surgery . The company is applying for regulatory approval in Australia and several other countries, and is expecting it to be approved for clinical use around 2024–5. It is intended to build a factory in the Kimberley region , where pearl shells are plentiful, which would grind
4515-637: Is because other hormones and proteins are involved in melanin production, the presence of which is genetically determined. In mice, a total of 100 genes are known to affect albinism. Most forms of albinism follow a recessive pattern of inheritance. However, this is not always the case. In palomino horses, genes coding for coat whiteness are dominant, and this is also true for several arctic mammals who possess dominant white colors which are pseudo-albinistic. However, these mammals differ from truly recessive albinos in that they still produce tyrosinase , and have normal eye pigmentation. In Japan, research has identified
4644-542: Is commonly decorated by mother of pearl. At the end of 19th century, Anukul Munsi was the first accomplished artist who successfully carved the shells of oysters to give a shape of human being which led to the invention of new horizon in Indian contemporary art. For the British Empire Exhibition in 1924, he received a gold medal. His eldest son Annada Munshi is credited with drawing Indian Swadesi Movement in
4773-407: Is crucial to metastasis and growth; non-pigmented tumors were larger than pigmented tumors, and spread far more easily. Pigmented and non-pigmented cells are both present in melanoma tumors , so that they can both be drug-resistant and metastatic. Mother of pearl Nacre is found in some of the most ancient lineages of bivalves , gastropods , and cephalopods . However, the inner layer in
4902-454: Is dark brown or black and insoluble, and DHICA -derived eumelanin which is lighter and soluble in alkali. Both eumelanins arise from the oxidation of tyrosine in specialized organelles called melanosomes . This reaction is catalyzed by the enzyme tyrosinase . The initial product, dopaquinone can transform into either 5,6-dihydroxyindole (DHI) or 5,6-dihydroxyindole-2-carboxylic acid (DHICA). DHI and DHICA are oxidized and then polymerize to form
5031-400: Is easier for the crack to continue into the viscoelastic and compliant organic matrix than going straight into another aragonite platelet. This results in the ductile protein phase deforming such that the crack changes directions and avoids the brittle ceramic phase. Based on experiments done on nacre-like synthetic materials , it is hypothesized that the compliant matrix needs to have
5160-547: Is not possible since albinism affects the whole plumage of a bird, not just part" and the definition of albinism precludes the possibility of "partial albinism" in which a mostly white bird shows some form of melanin pigmentation. "It is simply impossible, just like being 'partially pregnant' ". Conditions that are commonly termed "partial albino" include neural crest disorders such as piebaldism , Waardenburg syndrome , or other depigmentation conditions such as vitiligo . These conditions result from fundamentally different causes to
5289-525: Is not the case. In plants, albinism is characterised by partial or complete loss of chlorophyll pigments and incomplete differentiation of chloroplast membranes. Albinism in plants interferes with photosynthesis , which can reduce survivability. Some plant variations may have white flowers or other parts. However, these plants are not totally devoid of chlorophyll. Terms associated with this phenomenon are "hypochromia" and "albiflora". Biological pigments are substances produced by living organisms that have
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5418-433: Is occasionally associated with hearing impairments. However, when tested, there was no differences in responses between wild-type and albinistic European wels catfish ( Silurus glanis ) and South American bronze catfish ( Corydoras aeneus ). Similarly, Mexican blind cave fish ( Astyanax mexicanus ) do not differ in hearing sensitivity from the normally pigmented and eyed surface-dwelling populations. Fish lack melanin in
5547-407: Is of interest to scientists working on developing stronger materials. To achieve these effects, researchers take inspiration from nacre and use synthetic ceramics and polymers to mimic the " brick-and-mortar " structure, mineral bridges, and other hierarchical features. When dehydrated, nacre loses much of its strength and acts as a brittle material, like pure aragonite. The hardness of this material
5676-417: Is present in the skin and hair, etc. Pheomelanins (or phaeomelanins) impart a range of yellowish to reddish colors. Pheomelanins are particularly concentrated in the lips, nipples, glans of the penis, and vagina. When a small amount of eumelanin in hair (which would otherwise cause blond hair) is mixed with pheomelanin, the result is orange hair, which is typically called "red" or "ginger" hair . Pheomelanin
5805-451: Is sometimes used in the decorative grips of firearms, and in other gun furniture. Mother of pearl is sometimes used to make spoon -like utensils for caviar (i.e. caviar servers ) so as to not spoil the taste with metallic spoons. The biotech company Marine Biomedical, formed by a collaboration between the University of Western Australia Medical School and a Broome pearling business,
5934-408: Is stronger under compressive loads than tensile ones when the force is applied parallel or perpendicular to the platelets. As an oriented structure, nacre is highly anisotropic and as such, its mechanical properties are also dependent on the direction. A variety of toughening mechanisms are responsible for nacre's mechanical behavior. The adhesive force needed to separate the proteinaceous and
6063-403: Is the primary determinant of skin color . It is also found in hair, the pigmented tissue underlying the iris of the eye, and the stria vascularis of the inner ear . In the brain, tissues with melanin include the medulla and pigment-bearing neurons within areas of the brainstem , such as the locus coeruleus . It also occurs in the zona reticularis of the adrenal gland . The melanin in
6192-505: Is transported into the melanosome, reacting with dopaquinone to form cys-dopa. Cys-dopa then undergoes several transformations before forming pheomelanin. In chemical terms, pheomelanins differ from eumelanins in that the oligomer structure incorporates benzothiazine and benzothiazole units that are produced, instead of DHI and DHICA , when the amino acid L-cysteine is present. Pheomelanins, unlike euemanins, are rare in lower organisms with claims they are an "evolutionary innovation in
6321-436: Is weak. Most people's skin darkens when exposed to UV light, giving them more protection when it is needed. This is the physiological purpose of sun tanning . Dark-skinned people, who produce more skin-protecting eumelanin, have a greater protection against sunburn and the development of melanoma, a potentially deadly form of skin cancer, as well as other health problems related to exposure to strong solar radiation , including
6450-604: The Haliotidae , the Trochidae and the Turbinidae . Nacre is composed of hexagonal platelets of aragonite (a form of calcium carbonate ) 10–20 μm wide and 0.5 μm thick arranged in a continuous parallel lamina . Depending on the species, the shape of the tablets differs; in Pinna , the tablets are rectangular, with symmetric sectors more or less soluble. Whatever the shape of
6579-464: The epidermis and hair of mammals is primarily determined by the levels of eumelanin and pheomelanin in the examined tissue. In an average human individual, eumelanin is more abundant in tissues requiring photoprotection , such as the epidermis and the retinal pigment epithelium . In healthy subjects, epidermal melanin is correlated with UV exposure, while retinal melanin has been found to correlate with age, with levels diminishing 2.5-fold between
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#17331159847916708-465: The ionizing radiation of the sun's ultraviolet rays. In general, people whose ancestors lived for long periods in the regions of the globe near the equator have larger quantities of eumelanin in their skins. This makes their skins brown or black and protects them against high levels of exposure to the sun, which more frequently result in melanomas in lighter-skinned people. Not all the effects of pigmentation are advantageous. Pigmentation increases
6837-445: The lute family) typically feature nacre decorations, as does the related Middle Eastern oud (typically around the sound holes and on the back of the instrument). Bows of stringed instruments such as the violin and cello often have mother of pearl inlay at the frog. It is traditionally used on saxophone keytouches, as well as the valve buttons of trumpets and other brass instruments. The Middle Eastern goblet drum (darbuka)
6966-457: The mineral bridges may break, creating small asperities that roughen the aragonite-protein interface. The additional friction generated by the asperities helps the material withstand shear stresses. In nacre-like composites, the mineral bridges have also been shown to increase the flexural strength of the material because they can transfer stress in the material. Developing synthetic composites that exhibit similar mechanical properties as nacre
7095-448: The neural crest during embryonic development. Mature chromatophores are grouped into subclasses based on their colour under white light: Animals can also appear coloured due to structural colour , the result of coherent scattering perceived as iridescence . The structures themselves are colourless. Light typically passes through multiple layers and is reflected more than once. The multiple reflections compound one another and intensify
7224-521: The oxidation of the amino acid tyrosine is followed by polymerization . Pheomelanin is a cysteinated form containing poly benzothiazine portions that are largely responsible for the red or yellow tint given to some skin or hair colors. Neuromelanin is found in the brain. Research has been undertaken to investigate its efficacy in treating neurodegenerative disorders such as Parkinson's . Allomelanin and pyomelanin are two types of nitrogen free melanin. The phenotypic color variation observed in
7353-405: The photodegradation of certain vitamins such as riboflavins , carotenoids , tocopherol , and folate . Melanin in the eyes, in the iris and choroid , helps protect from ultraviolet and high-frequency visible light ; people with blue, green, and grey eyes are more at risk of sun-related eye problems. Furthermore, the ocular lens yellows with age, providing added protection. However,
7482-588: The radioprotective effects of melanin against gamma radiation come from the laboratories and research groups of Irma Mosse. Mosse began in radiobiology in the Soviet era, was increasingly supported by government funding in the wake of the discovery of radiotrophic microbes in Chernobyl , and as of 2022 continues under the Belarusian Institute of Genetics and Cytology . Her most significant contribution
7611-447: The retinal pigment epithelium (RPE) also may be implicated in the downregulation of rod outer segment phagocytosis by the RPE. This phenomenon has been attributed in part to foveal sparing in macular degeneration . Heavily pigmented melanoma cells have a Young's modulus of about 4.93 kPa, compared to non-pigmented cells, with a value of 0.98 kPa. The elasticity of melanoma cells
7740-696: The 19th century. Widely used for pearl buttons especially during the 1900s, were the shells of the great green turban snail Turbo marmoratus and the large top snail, Tectus niloticus . The international trade in mother of pearl is governed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora , an agreement signed by more than 170 countries. Both black and white nacre are used for architectural purposes. The natural nacre may be artificially tinted to almost any color. Nacre tesserae may be cut into shapes and laminated to
7869-558: The 20/60 to 20/400 range. In addition, two forms of albinism, with approximately 1 in 2,700 most prevalent among people of Puerto Rican origin, are associated with mortality beyond melanoma-related deaths. The connection between albinism and deafness is well known, though poorly understood. In his 1859 treatise On the Origin of Species , Charles Darwin observed that "cats which are entirely white and have blue eyes are generally deaf". In humans, hypopigmentation and deafness occur together in
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#17331159847917998-513: The Albino Squirrel Preservation Society. They have also been protected in studies on their ecology, sociology and behaviour. Studies on medaka fish in the laboratory, i.e. with no predators, sufficient food supply, controlled temperatures, etc., found that albinos had considerably reduced viability; from 800 albino embryos, only 29 survived to full adulthood. Early studies on fish led some researchers to describe albinism as
8127-423: The ability of melanin to act as an antioxidant is directly proportional to its degree of polymerization or molecular weight . Suboptimal conditions for the effective polymerization of melanin monomers may lead to formation of pro-oxidant melanin with lower-molecular-weight, implicated in the causation and progression of macular degeneration and melanoma . Signaling pathways that upregulate melanization in
8256-401: The aragonite phases is high, indicating that there are molecular interactions between the components. In laminated structures with hard and soft layers, a model system that can be applied to understand nacre, the fracture energy and fracture strength are both larger than those values characteristic of the hard material only. Specifically, this structure facilitates crack deflection, since it
8385-482: The behaviour of albinos in the wild, e.g. leaping from branch to branch, is similar to pigmented squirrels. A 2012 survey of the literature reported that in India, there were several records of albino mammals including the tiger , lesser mouse-tailed bat , chital , common palm civet , northern palm squirrel , five-striped palm squirrel and wild boar . Albino macaques have been reported in several occasions including
8514-473: The best choice for scientific studies due to the consequences of albinism (e.g. hearing and visual impairments). Many individual albino mammals are in captivity and were caught while young. However, the survival prospects of these creatures into adulthood outside of captivity are uncertain. It is doubtful whether these individuals would have survived to become adults without the protection and care they receive in captivity. It has been claimed that "Squirrels are
8643-413: The centre of the retina is under-developed and there is a deficit of rod cells, which detect light levels; the central ganglion cell density is approximately 25% below normal (except for the eastern gray squirrel ). In nearly all mammals, the overwhelming majority of photoreceptors are rods rather than cones, which detect color. Albinism specifically affects the rod cells, but the number and distribution of
8772-416: The colours. Structural colour differs according to the observer's position whereas pigments appear the same regardless of the angle-of-view. Animals that show iridescence include mother of pearl seashells, fish, and peacocks. These are just a few examples of animals with this quality, but it is most pronounced in the butterfly family. The primary function of pigments in plants is photosynthesis , which uses
8901-406: The cones is unaffected. In contrast, the retinas of birds are cone rich, meaning that the vision of albino birds is affected less than albino mammals. Melanin protects the skin from ultra-violet radiation in sunlight. Melanosomes block harmful electromagnetic radiation from the sun while allowing beneficial frequencies to enter the body. This means some animals may die from UV radiation due to
9030-688: The costs, some individuals do reach adult age and breeding status. Albino dolphins were first sighted in the Gulf of Mexico in 1962. Since 1994, three further individuals have been seen. These tend to be pink in colour due to blood vessels showing through the blubber and unpigmented skin. A report published in 2008 stated that in marine mammals, "anomalously white" individuals have been reported for 21 cetacean species and seven pinniped species but there were no known reports of anomalously white sea otters ( Enhydra lutris ) or sirenians . Whales and dolphins also may appear white if extensively scarred, or covered with
9159-494: The crack gets pinned. But, higher statistical variations generates very weak regions which allows the crack to propagate without much resistance causing the fracture toughness to decrease. Studies have shown that this weak structural defects act as dissipative topological defects coupled by an elastic distortion. The process of how nacre is formed is not completely clear. It has been observed in Pinna nobilis , where it starts as tiny particles (~50–80 nm) grouping together inside
9288-893: The definition of albinism precludes the possibility of "partial albinism" in which a mostly white bird shows some form of melanin pigmentation. "It is simply impossible, just like being 'partially pregnant'. As with other animals, it has been stated that for fish to be properly described as "albino", they must have a white body and pink or red eyes. Zebrafish have three types of chromatophores—iridophores, melanophores, and xanthophores—which produce silver, black, and yellow pigmentation respectively. Zebrafish that lack iridophores are known as roy mutants , those that lack melanophores as albino mutants , and those which lack both melanophores and iridophores are ruby mutants . The gross eye morphology, feeding and swimming behaviours between wild-type and albino zebrafish were indistinguishable, except under dim or bright light or low contrast. In mammals, albinism
9417-406: The derived allele SLC24A5 , a known cause of nonsyndromic oculocutaneous albinism. It is an autosomal recessive disorder characterized by a congenital reduction or absence of melanin pigment in the skin, hair, and eyes. The estimated frequency of OCA2 among African-Americans is 1 in 10,000, which contrasts with a frequency of 1 in 36,000 in white Americans. In some African nations, the frequency of
9546-552: The disorder is even higher, ranging from 1 in 2,000 to 1 in 5,000. Another form of Albinism, the "yellow oculocutaneous albinism", appears to be more prevalent among the Amish , who are of primarily Swiss and German ancestry. People with this IB variant of the disorder commonly have white hair and skin at birth, but rapidly develop normal skin pigmentation in infancy. Ocular albinism affects not only eye pigmentation but visual acuity, as well. People with albinism typically test poorly, within
9675-597: The enzymes required to synthesize melanin have normal auditory function. Instead, the absence of melanocytes in the stria vascularis of the inner ear results in cochlear impairment, though the reasons for this are not fully understood. In Parkinson's disease, a disorder that affects neuromotor functioning, there is decreased neuromelanin in the substantia nigra and locus coeruleus as a consequence of specific dropping out of dopaminergic and noradrenergic pigmented neurons. This results in diminished dopamine and norepinephrine synthesis. While no correlation between race and
9804-442: The epidermis ranges from around 0 μg/mg in albino epidermal tissue to >10 μg/mg in darker tissue. In the human skin, melanogenesis is initiated by exposure to UV radiation , causing the skin to darken. Eumelanin is an effective absorbent of light; the pigment is able to dissipate over 99.9% of absorbed UV radiation. Because of this property, eumelanin is thought to protect skin cells from UVA and UVB radiation damage, reducing
9933-576: The eumelanins Detailed metabolic pathways can be found in the KEGG database (see External links ). Melanin is brown, non-refractile, and finely granular with individual granules having a diameter of less than 800 nanometers. This differentiates melanin from common blood breakdown pigments , which are larger, chunky, and refractile, and range in color from green to yellow or red-brown. In heavily pigmented lesions, dense aggregates of melanin can obscure histologic detail. A dilute solution of potassium permanganate
10062-463: The first and ninth decades of life, which has been attributed to oxidative degradation mediated by reactive oxygen species generated via lipofuscin -dependent pathways. In the absence of albinism or hyperpigmentation , the human epidermis contains approximately 74% eumelanin and 26% pheomelanin, largely irrespective of skin tone, with eumelanin content ranging between 71.8–78.9%, and pheomelanin varying between 21.1–28.2%. Total melanin content in
10191-625: The form of Indian advertising. Anukul Charan Munshi's third son Manu Munshi was one of the finest mother of pearl artists in the middle of 20th century. As the best example of "Charu and Karu art of Bengal," the former Chief Minister of West Bengal , Dr. Bidhan Chandra Roy , sent Manu's artwork, "Gandhiji's Noakhali Abhiyan", to the United States . Numerous illustrious figures, such as Satyajit Ray , Bidhan Chandra Roy , Barrister Subodh Chandra Roy, Subho Tagore , Humayun Kabir , Jehangir Kabir , as well as his elder brother Annada Munshi, were among
10320-758: The formation of this capsule is thought to aid in killing them. Some types of fungi, called radiotrophic fungi , appear to be able to use melanin as a photosynthetic pigment that enables them to capture gamma rays and harness this energy for growth. In fish , melanin occurs not only in the skin but also in internal organs such as eyes. Most fish species use eumelanin, but Stegastes apicalis and Cyprinus carpio use pheomelanin instead. The darker feathers of birds owe their color to melanin and are less readily degraded by bacteria than unpigmented ones or those containing carotenoid pigments. Feathers that contain melanin are also 39% more resistant to abrasion than those that do not because melanin granules help fill
10449-462: The full height of the layer of nacre. They continue to grow until they meet the surrounding bricks. This produces the hexagonal close-packing characteristic of nacre. The growth of these bricks can be initiated in various ways such as from randomly scattered elements within the organic layer, well-defined arrangements of proteins, or they may expand from mineral bridges coming from the layer underneath. What sets nacre apart from fibrous aragonite,
10578-452: The great majority of mollusc shells is porcellaneous , not nacreous, and this usually results in a non-iridescent shine, or more rarely in non-nacreous iridescence such as flame structure as is found in conch pearls. The outer layer of cultured pearls and the inside layer of pearl oyster and freshwater pearl mussel shells are made of nacre. Other mollusc families that have a nacreous inner shell layer include marine gastropods such as
10707-590: The green pigment chlorophyll along with several red and yellow pigments including porphyrins , carotenoids , anthocyanins and betalains . Definitions of albinism vary and are inconsistent. While they are clear and precise for humans and other mammals, this is because the majority of mammals have only one pigment, melanin. Many animals have pigments other than melanin, and some also have structural colours. Some definitions of albinism, whilst taking most taxa into account, ignore others. So, "a person or animal with very pale skin, white hair or fur, and pink eyes caused by
10836-467: The heat load in hot climates, and dark-skinned people absorb 30% more heat from sunlight than do very light-skinned people, although this factor may be offset by more profuse sweating. In cold climates dark skin entails more heat loss by radiation. Pigmentation also hinders synthesis of vitamin D . Since pigmentation appears to be not entirely advantageous to life in the tropics, other hypotheses about its biological significance have been advanced; for example
10965-425: The increased nicotine dependence and lower smoking cessation rates in darker pigmented individuals. Melanocytes insert granules of melanin into specialized cellular vesicles called melanosomes . These are then transferred into the keratinocyte cells of the human epidermis . The melanosomes in each recipient cell accumulate atop the cell nucleus , where they protect the nuclear DNA from mutations caused by
11094-616: The ink used by many cephalopods (see cephalopod ink ) as a defense mechanism against predators. Melanins also protect microorganisms, such as bacteria and fungi, against stresses that involve cell damage such as UV radiation from the sun and reactive oxygen species . Melanin also protects against damage from high temperatures, chemical stresses (such as heavy metals and oxidizing agents ), and biochemical threats (such as host defenses against invading microbes). Therefore, in many pathogenic microbes (for example, in Cryptococcus neoformans ,
11223-653: The inner ear, meaning that hearing in fishes is less likely to be affected by albinism than in mammals. There are several reports of total albinism in both freshwater and marine fish, however, frequently captured albino fish are only reported in aquarium magazines and local newspapers. The incidence of albinism can be artificially increased in fish by exposing the eggs to heavy metals (e.g. arsenic, cadmium, copper, mercury, selenium, zinc). Melanin Melanin ( / ˈ m ɛ l ə n ɪ n / ; from Ancient Greek μέλας ( mélas ) 'black, dark')
11352-496: The lack of protection from UV radiation and their lack of camouflage to avoid predators. It is a common misconception that all albino animals have characteristic pink or red eyes (resulting from the lack of pigment in the iris allowing the blood vessels of the retina to be visible); this is not the case for some forms of albinism. Familiar albino animals include in-bred strains of laboratory animals (rats, mice and rabbits), but populations of naturally occurring albino animals exist in
11481-489: The largest portion, approximately 60–70%, followed by DHICA-eumelanin at 25–35%, and pheomelanin only 2–8%. Notably, while an enrichment of DHI-eumelanin occurs in during sun tanning , it is accompanied by a decrease in DHICA-eumelanin and pheomelanin. A small amount of black eumelanin in the absence of other pigments causes grey hair. A small amount of eumelanin in the absence of other pigments causes blond hair. Eumelanin
11610-441: The lens also becomes more rigid with age, losing most of its accommodation —the ability to change shape to focus from far to near—a detriment due probably to protein crosslinking caused by UV exposure. Recent research suggests that melanin may serve a protective role other than photoprotection. Melanin is able to effectively chelate metal ions through its carboxylate and phenolic hydroxyl groups, often much more efficiently than
11739-610: The level of neuromelanin in the substantia nigra has been reported, the significantly lower incidence of Parkinson's in blacks than in whites has "prompt[ed] some to suggest that cutaneous melanin might somehow serve to protect the neuromelanin in substantia nigra from external toxins." In addition to melanin deficiency, the molecular weight of the melanin polymer may be decreased by various factors such as oxidative stress, exposure to light, perturbation in its association with melanosomal matrix proteins , changes in pH , or in local concentrations of metal ions. A decreased molecular weight or
11868-520: The males compared to the wild-type; albino males had higher mount frequencies than wild-type males. In addition, the albinos had greater differential fertilizing capacity. Albinism can also occur in marsupials and monotremes , such as echidnas , kangaroos , koalas , possums , wallabies and wombats . The costs of albinism for marine mammals may include reduced heat absorption in colder waters, poor camouflage from predators, increased sensitivity to sunlight, and impaired visual communication. Despite
11997-454: The material that drew them towards each other as the layers built up until they merged and cancelled each other out. Later layers of nacre were found to be uniform and ordered in structure. Nacre is secreted by the epithelial cells of the mantle tissue of various molluscs. The nacre is continuously deposited onto the inner surface of the shell, the iridescent nacreous layer , commonly known as mother of pearl . The layers of nacre smooth
12126-425: The mechanical performance (stiffness, strength, and energy absorption) because statistical variation precipitates localization of deformation. However, the negative effects of statistical variations can be offset by interfaces with large strain at failure accompanied by strain hardening. On the other hand, the fracture toughness of nacre increases with moderate statistical variations which creates tough regions where
12255-415: The nacre into a product fit for use in biomedical products. Future applications could include dental fillings and spinal surgery . In 2012, researchers created calcium-based nacre in the laboratory by mimicking its natural growth process. In 2014, researchers used lasers to create an analogue of nacre by engraving networks of wavy 3D "micro-cracks" in glass. When the slides were subjected to an impact,
12384-412: The nacre layer is formed of single crystals in a hexagonal close packing . In gastropods , crystals are twinned , and in cephalopods , they are pseudohexagonal monocrystals, which are often twinned. The main commercial sources of mother of pearl have been the pearl oyster , freshwater pearl mussels, and to a lesser extent the abalone , popular for their sturdiness and beauty in the latter half of
12513-612: The normal development of various parts of the eye, including the iris, retina, eye muscles, and optic nerve. The absence of melanin results in abnormal development of eyes and leads to problems with focusing, and depth perception. The eyes of albino animals appear red because the colour of the red blood cells in the retina can be seen through the iris, which has no pigment to obscure this. Some albino animals may have pale-blue eyes due to other colour generating processes. Albino vertebrates exposed to intense light typically lose photoreceptors due to apoptosis . In all albino mammals studied,
12642-424: The only known albino mammal to survive successfully in the wild". The retina of the squirrel ( Sciurus carolinensis ) is unusual for mammals as it is rich in cones. Central cell densities are less than 5% lower in albino squirrels than in pigmented individuals. This relatively minor disruption to vision is thought to assist in the survivability of albino squirrels in the wild. This is supported by observations that
12771-454: The organic interlayers. The interlocking of bricks of nacre has large impact on both the deformation mechanism as well as its toughness. Tensile , shear , and compression tests, Weibull analysis, nanoindentation , and other techniques have all been used to probe the mechanical properties of nacre. Theoretical and computational methods have also been developed to explain the experimental observations of nacre's mechanical behavior. Nacre
12900-445: The other known forms of melanin. This protection has been demonstrated with radiation experiments on human cells and bacteria, opening up the possibility of applications in space travel. Trichochromes (formerly called trichosiderins) are pigments produced from the same metabolic pathway as the eumelanins and pheomelanins, but unlike those molecules they have low molecular weight. They occur in some red human hair. In humans, melanin
13029-550: The oxidation of indole-5,6-quinone by the tyrosinase type polyphenol oxidase from tyrosine and catecholamines leading to the formation of catechol melanin. Despite this many plants contain compounds which inhibit the production of melanins. It is now understood that melanins do not have a single structure or stoichiometry. Nonetheless, chemical databases such as PubChem include structural and empirical formulae; typically 3,8-Dimethyl-2,7-dihydrobenzo[1,2,3- cd :4,5,6- c ′ d ′]diindole-4,5,9,10-tetrone . This can be thought of as
13158-507: The patrons of his works of art. "Indira Gandhi" was one of his famous mother of pearl works of art. He is credited with portraying Tagore in various creative stances that were skillfully carved into metallic plates. His cousin Pratip Munshi was also a famed mother of pearl artist. Mother of pearl buttons are used in clothing either for functional or decorative purposes. The Pearly Kings and Queens are an elaborate example of this. It
13287-470: The powerful chelating ligand ethylenediaminetetraacetate (EDTA). Thus, it may serve to sequester potentially toxic metal ions, protecting the rest of the cell. This hypothesis is supported by the fact that the loss of neuromelanin, observed in Parkinson's disease, is accompanied by an increase in iron levels in the brain. Evidence exists for a highly cross-linked heteropolymer bound covalently to matrix scaffolding melanoproteins . It has been proposed that
13416-608: The rare Waardenburg's syndrome , predominantly observed among the Hopi in North America. The incidence of albinism in Hopi Indians has been estimated as approximately 1 in 200 individuals. Similar patterns of albinism and deafness have been found in other mammals, including dogs and rodents. However, a lack of melanin per se does not appear to be directly responsible for deafness associated with hypopigmentation, as most individuals lacking
13545-401: The rate is once in every 1,764 births. Some species, such as white peacocks, swans and geese, are not believed to be true albinos, as they do not have red eyes, rather, their colouration is suggested to be the expression of a white fur or feather gene, not a lack of melanin. Melanin has several functions in most mammals and other animals; these are disrupted by albinism. Melanin functions in
13674-423: The related Parkinson's disease . Up until the 1960s, melanin was classified into eumelanin and pheomelanin. However, in 1955, a melanin associated with nerve cells was discovered, neuromelanin. In 1972 a water-soluble form, pyomelanin was discovered. In 1976, allomelanin, the fifth form of the melanins was found in nature. Peptidomelanin is another water-soluble form of melanin. It was found to be secreted into
13803-469: The rest of the world through migration between 80,000 and 50,000 years ago, in some areas interbreeding with certain archaic human species ( Neanderthals , Denisovans , and possibly others). The first modern humans had darker skin as the indigenous people of Africa today. Following migration and settlement in Asia and Europe, the selective pressure dark UV-radiation protecting skin decreased where radiation from
13932-442: The risk of folate depletion and dermal degradation. Exposure to UV radiation is associated with increased risk of malignant melanoma , a cancer of melanocytes (melanin cells). Studies have shown a lower incidence for skin cancer in individuals with more concentrated melanin, i.e. darker skin tone . Eumelanin has two forms linked to 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA). DHI-derived eumelanin
14061-553: The same rate. Furthermore, in certain species, albino animals may be excluded from families or other groups, or rejected as mates. On the other hand, there is also evidence for positive selection for albinism in some animals, as well as cultural selection favoring albino people in some human societies, which results in the increase of genes associated with albinism. The founder effect may explain why some animal populations become selected for albinism. The novelty of albino animals has occasionally led to their protection by groups such as
14190-436: The scale of this pattern matches the wavelength of visible light, structural coloration arises: giving a number of species an iridescent color. Arachnids are one of the few groups in which melanin has not been easily detected, though researchers found data suggesting spiders do in fact produce melanin. Some moth species, including the wood tiger moth , convert resources to melanin to enhance their thermoregulation. As
14319-646: The seven types of oculocutaneous albinism that have been identified in humans (and confirmed in some other animals) and the use of the term "partial albino" is therefore misleading. One definition states that "albinism, (from the Latin albus, meaning "white"), hereditary condition characterized by the absence of pigment in the eyes, skin, hair, scales, or feathers", however, this does not encompass invertebrates, nor does it include plants. Furthermore, it could be interpreted that "...absence of pigment..." does not include an absence of structural colours. The lack of clarity about
14448-412: The several other pigments that non-mammalian animals have and also structural colouration. For example, "Absence of the pigment melanin in the eyes, skin, hair, scales, or feathers." refers only to the pigment melanin. Because of the various uses of different terms applied to colouration, some authors have indicated that the colour of the eyes is the defining characteristic of albinism, e.g. "This leads to
14577-400: The shell surface and help defend the soft tissues against parasites and damaging debris by entombing them in successive layers of nacre, forming either a blister pearl attached to the interior of the shell, or a free pearl within the mantle tissues. The process is called encystation and it continues as long as the mollusc lives. The form of nacre varies from group to group. In bivalves ,
14706-417: The shell wall, but the direction of the other axes varies between groups. Adjacent tablets have been shown to have dramatically different c-axis orientation, generally randomly oriented within ~20° of vertical. In bivalves and cephalopods, the b- axis points in the direction of shell growth, whereas in the monoplacophora it is the a -axis that is this way inclined. This mixture of brittle platelets and
14835-419: The skin and eyes, only eumelanin is present. In some bird species, the colour is completely caused by eumelanin, however, both types of melanin are found in most species. In birds, albinism has been defined as "a total lack of both melanins in feathers, eyes and skin as a result of an inherited absence of tyrosinase", however, this ignores the effects of other pigments and structural colours. An albino bird has
14964-477: The skin is produced by melanocytes , which are found in the basal layer of the epidermis . Although, in general, human beings possess a similar concentration of melanocytes in their skin, the melanocytes in some individuals and ethnic groups produce variable amounts of melanin. The ratio of eumelanin (74%) and pheomelanin (26%) in the epidermis is constant regardless of the degree of pigmentation. Some humans have very little or no melanin synthesis in their bodies,
15093-408: The space between the keratin strands that form feathers. Pheomelanin synthesis in birds implies the consumption of cysteine, a semi‐essential amino acid that is necessary for the synthesis of the antioxidant glutathione (GSH) but that may be toxic if in excess in the diet. Indeed, many carnivorous birds, which have a high protein content in their diet, exhibit pheomelanin‐based coloration. Melanin
15222-480: The sun was less intense. This resulted in the current range of human skin color. Of the two common gene variants known to be associated with pale human skin, Mc1r does not appear to have undergone positive selection, while SLC24A5 has undergone positive selection. As with peoples having migrated northward, those with light skin migrating toward the equator acclimatize to the much stronger solar radiation. Nature selects for less melanin when ultraviolet radiation
15351-562: The surrounding medium by germinating Aspergillus niger (strain: melanoliber) spores. Peptidomelanin is formed as a copolymer between L-DOPA eumelanin and short peptides that form a 'corona', that are responsible for the substance's solubility. The peptide chains are linked to the L-DOPA core polymer via peptide bonds. This lead to a proposed biosynthetic process involving the hydroxylation of tyrosinylated peptides formed via proteases during sporogenesis, which are then incorporated autoxidatively into
15480-593: The tablets, the smallest units they contain are irregular rounded granules. These layers are separated by sheets of organic matrix (interfaces) composed of elastic biopolymers (such as chitin , lustrin and silk -like proteins ). Nacre appears iridescent because the thickness of the aragonite platelets is close to the wavelength of visible light . These structures interfere constructively and destructively with different wavelengths of light at different viewing angles, creating structural colours . The crystallographic c- axis points approximately perpendicular to
15609-478: The targeted tissue. In a similar manner, melanin can complicate laser treatment of other dermatological conditions in people with darker skin. Freckles and moles are formed where there is a localized concentration of melanin in the skin. They are highly associated with pale skin. Nicotine has an affinity for melanin-containing tissues because of its precursor function in melanin synthesis or its irreversible binding of melanin. This has been suggested to underlie
15738-593: The term is furthered when the name of an animal includes the term "albino" although the animals (clearly) do not have the condition. For example, the albino gaur has this name because it is ash-grey whereas other gaur are almost black. A clear definition appears to be – "Congenital absence of any pigmentation or colouration in a person, animal, or plant, resulting in white hair and pink eyes in mammals." Whilst this does not state specifically that non-mammalian albino animals (or plants) are white, this can be inferred from "...absence of any pigmentation or colouration..." Due to
15867-569: The tetrapod lineage" but recent research finds them also in some fish. Neuromelanin (NM) is an insoluble polymer pigment produced in specific populations of catecholaminergic neurons in the brain. Humans have the largest amount of NM, which is present in lesser amounts in other primates, and totally absent in many other species. The biological function remains unknown, although human NM has been shown to efficiently bind transition metals such as iron, as well as other potentially toxic molecules. Therefore, it may play crucial roles in apoptosis and
15996-529: The thin layers of elastic biopolymers makes the material strong and resilient, with a Young's modulus of 70 GPa and a yield stress of roughly 70 MPa (when dry). Strength and resilience are also likely to be due to adhesion by the "brickwork" arrangement of the platelets, which inhibits transverse crack propagation. This structure, spanning multiple length sizes, greatly increases its toughness , making it almost as strong as silicon . The mineral–organic interface results in enhanced resilience and strength of
16125-498: The two eumelanins. In natural conditions, DHI and DHICA often co-polymerize, resulting in a range of eumelanin polymers. These polymers contribute to the variety of melanin components in human skin and hair, ranging from light yellow/red pheomelanin to light brown DHICA-enriched eumelanin and dark brown or black DHI-enriched eumelanin. These final polymers differ in solubility and color. Analysis of highly pigmented ( Fitzpatrick type V and VI) skin finds that DHI-eumelanin comprises
16254-521: The varied use and interpretation of the term "albino", written reports of albinistic organisms can often not be verified. Melanin is an organic pigment that produces most of the colour seen in mammals. Depending on how it is created, melanin comes in two colour ranges, eumelanin (producing dark browns and blacks) and pheomelanin (producing light reddish tans and blondes). The dark and light melanins have their influence either alone or in conjunction, making either plain or multi-coloured coats. Sometimes, in
16383-421: The wild, e.g., Mexican cave tetra . Albinism is a well-recognized phenomenon in molluscs, both in the shell and in the soft parts. It has been claimed by some that albinism can occur for a number of reasons aside from inheritance, including genetic mutations, diet, living conditions, age, disease, or injury. However, this is contrary to definitions where the condition is inherited. Oculocutaneous albinism (OCA)
16512-628: The wood tiger moth has populations over a large range of latitudes, it has been observed that more northern populations showed higher rates of melanization. In both yellow and white male phenotypes of the wood tiger moth, individuals with more melanin had a heightened ability to trap heat but an increased predation rate due to a weaker and less effective aposematic signal. Melanin protects Drosophila flies and mice against DNA damage from non-UV radiation. Important studies in Drosophila models include Hopwood et al. , 1985. Much of our understanding of
16641-523: Was observed from the Polooni area in Malappuram district and Chaliyam area of Calicut district (Kerala). As albinism is observed in those areas where the density of these mammals is comparatively low, it is concluded that continuous inbreeding could be the reason for expression of albinism. A study on albinistic prairie voles ( Microtus ochrogaster ) found that albinism in this species conferred an advantage for
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