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77-532: About 10–11; see text Larches are deciduous conifers in the genus Larix , of the family Pinaceae (subfamily Laricoideae ). Growing from 20 to 45 metres (65 to 150 feet) tall, they are native to the cooler regions of the northern hemisphere, where they are found in lowland forests in the high latitudes, and high in mountains further south. Larches are among the dominant plants in the boreal forests of Siberia and Canada . Although they are conifers , larches are deciduous trees that lose their needles in
154-399: A behavior known as " marcescence " whereby dead leaves are not shed in the fall and remain on the tree until being blown off by the weather. This is caused by incomplete development of the abscission layer. It is mainly seen in the seedling and sapling stage, although mature trees may have marcescence of leaves on the lower branches. A number of deciduous plants remove nitrogen and carbon from
231-459: A cell nucleus. Chromosomes in humans can be divided into two types: autosomes (body chromosome(s)) and allosome ( sex chromosome (s)). Certain genetic traits are linked to a person's sex and are passed on through the sex chromosomes. The autosomes contain the rest of the genetic hereditary information. All act in the same way during cell division. Human cells have 23 pairs of chromosomes (22 pairs of autosomes and one pair of sex chromosomes), giving
308-883: A cool and fairly humid climate and for this reason they are found in the mountains of the temperate zones, while in the northernmost boreal zones they are also found in the plain. Larch trees go further north than all, reaching in North America and Siberia the tundra and polar ice. The larches are pioneer species not very demanding towards the soil and they are very long-lived trees. They live in pure or mixed forests together with other conifers or more rarely with broad-leaved trees. L. potaninii Batalin L. occidentalis Nuttall L. decidua Miller L. cajanderi Mayr L. griffithii Hooker L. gmelinii (Rupr.) Kuzen. L. kaempferi (Lamb.) Carrière L. laricina (Du Roi) Koch L. lyallii Parlatore L. sibirica Ledeb. In
385-418: A crucial role in genetic diversity . If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation , the cell may undergo mitotic catastrophe . This will usually cause the cell to initiate apoptosis , leading to its own death , but the process is occasionally hampered by cell mutations that result in the progression of cancer . The term 'chromosome'
462-650: A different genetic configuration , and Boveri was able to test and confirm this hypothesis. Aided by the rediscovery at the start of the 1900s of Gregor Mendel 's earlier experimental work, Boveri identified the connection between the rules of inheritance and the behaviour of the chromosomes. Two generations of American cytologists were influenced by Boveri: Edmund Beecher Wilson , Nettie Stevens , Walter Sutton and Theophilus Painter (Wilson, Stevens, and Painter actually worked with him). In his famous textbook, The Cell in Development and Heredity , Wilson linked together
539-602: A greater rate of transpiration (and hence CO 2 uptake as this occurs when stomata are open) during the summer growth period. The deciduous characteristic has developed repeatedly among woody plants. Trees include maple , many oaks and nothofagus , elm , beech , aspen , and birch , among others, as well as a number of coniferous genera , such as larch and Metasequoia . Deciduous shrubs include honeysuckle , viburnum , and many others. Most temperate woody vines are also deciduous, including grapes , poison ivy , Virginia creeper , wisteria , etc. The characteristic
616-489: A higher chance of bearing a child with a chromosome disorder. Abnormal numbers of chromosomes or chromosome sets, called aneuploidy , may be lethal or may give rise to genetic disorders. Genetic counseling is offered for families that may carry a chromosome rearrangement. The gain or loss of DNA from chromosomes can lead to a variety of genetic disorders . Human examples include: Exposure of males to certain lifestyle, environmental and/or occupational hazards may increase
693-439: A non-colored state. Otto Bütschli was the first scientist to recognize the structures now known as chromosomes. In a series of experiments beginning in the mid-1880s, Theodor Boveri gave definitive contributions to elucidating that chromosomes are the vectors of heredity , with two notions that became known as 'chromosome continuity' and 'chromosome individuality'. Wilhelm Roux suggested that every chromosome carries
770-474: A patchwork of leafy and leafless trees. Chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism . In most chromosomes, the very long thin DNA fibers are coated with nucleosome -forming packaging proteins ; in eukaryotic cells, the most important of these proteins are the histones . Aided by chaperone proteins , the histones bind to and condense
847-481: A semi-ordered structure, where it is wrapped around histones (structural proteins), forming a composite material called chromatin. The packaging of DNA into nucleosomes causes a 10 nanometer fibre which may further condense up to 30 nm fibres Most of the euchromatin in interphase nuclei appears to be in the form of 30-nm fibers. Chromatin structure is the more decondensed state, i.e. the 10-nm conformation allows transcription. During interphase (the period of
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#1733085652362924-481: A single bud. The leaves (light green) are needle-like, 2 to 5 cm ( 3 ⁄ 4 to 2 in) long, slender (under 1 cm or 1 ⁄ 2 in wide). Larches are among the few deciduous conifers, which are usually evergreen. Other deciduous conifers include the golden larch Pseudolarix amabilis , the dawn redwood Metasequoia glyptostroboides , the Chinese swamp cypress Glyptostrobus pensilis and
1001-542: A total of 46 per cell. In addition to these, human cells have many hundreds of copies of the mitochondrial genome . Sequencing of the human genome has provided a great deal of information about each of the chromosomes. Below is a table compiling statistics for the chromosomes, based on the Sanger Institute 's human genome information in the Vertebrate Genome Annotation (VEGA) database . Number of genes
1078-440: Is hexaploid , having six copies of seven different chromosome types for a total of 42 chromosomes. Normal members of a particular eukaryotic species all have the same number of nuclear chromosomes. Other eukaryotic chromosomes, i.e., mitochondrial and plasmid-like small chromosomes, are much more variable in number, and there may be thousands of copies per cell. Asexually reproducing species have one set of chromosomes that are
1155-598: Is a deciduous woody shrub found in Japan . Forests where a majority of the trees lose their foliage at the end of the typical growing season are called deciduous forests. These forests are found in many areas worldwide and have distinctive ecosystems, understory growth, and soil dynamics. Two distinctive types of deciduous forests are found growing around the world. Temperate deciduous forest biomes are plant communities distributed in North and South America, Asia, Southern slopes of
1232-414: Is almost exclusive guest of the gen. Larix . Other diseases are given by mushrooms, fungal rusts, bacteria and insects. Larch wood is valued for its tough, waterproof and durable qualities. Top quality knot -free timber is in great demand for building yachts and other small boats , for exterior cladding of buildings, and interior paneling. The timber is somewhat resistant to rot when in contact with
1309-413: Is an estimate, as it is in part based on gene predictions . Total chromosome length is an estimate as well, based on the estimated size of unsequenced heterochromatin regions. Based on the micrographic characteristics of size, position of the centromere and sometimes the presence of a chromosomal satellite , the human chromosomes are classified into the following groups: In general, the karyotype
1386-454: Is another probable hybrid still unresolved. Larches are associated with a number of mycorrhizal fungal species, including some species which primarily or only associate with larch. One of the most prominent of these species is the larch bolete Suillus grevillei . Larch is used as a food plant by the larvae of a number of Lepidoptera species. Larches are prone to the fungal canker disease Lachnellula ssp. (larch canker); this
1463-700: Is completed (marked by the transition from bright green spring leaves to dark green summer ones) the chlorophyll level in the leaves remains stable until cool temperatures arrive in autumn. When autumn arrives and the days are shorter or when plants are drought-stressed, the chlorophyll steadily breaks down, allowing other pigments present in the leaf to become apparent and resulting in non-green colored foliage. The brightest leaf colors are produced when days grow short and nights are cool, but remain above freezing. These other pigments include carotenoids that are yellow, brown, and orange. Anthocyanin pigments produce red and purple colors, though they are not always present in
1540-620: Is duplicated ( S phase ), and the two copies are joined by a centromere —resulting in either an X-shaped structure if the centromere is located equatorially, or a two-armed structure if the centromere is located distally; the joined copies are called ' sister chromatids '. During metaphase, the duplicated structure (called a 'metaphase chromosome') is highly condensed and thus easiest to distinguish and study. In animal cells, chromosomes reach their highest compaction level in anaphase during chromosome segregation . Chromosomal recombination during meiosis and subsequent sexual reproduction plays
1617-400: Is formed between the leaf petiole and the stem. This layer is formed in the spring during active new growth of the leaf; it consists of layers of cells that can separate from each other. The cells are sensitive to a plant hormone called auxin that is produced by the leaf and other parts of the plant. When auxin coming from the leaf is produced at a rate consistent with that from the body of
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#17330856523621694-559: Is organized into a structure called the nucleoid . The nucleoid is a distinct structure and occupies a defined region of the bacterial cell. This structure is, however, dynamic and is maintained and remodeled by the actions of a range of histone-like proteins, which associate with the bacterial chromosome. In archaea , the DNA in chromosomes is even more organized, with the DNA packaged within structures similar to eukaryotic nucleosomes. Certain bacteria also contain plasmids or other extrachromosomal DNA . These are circular structures in
1771-482: Is particularly a problem on sites prone to late spring frosts, which cause minor injuries to the tree allowing entry to the fungal spores. In Canada , this disease was first detected in 1980 and is particularly harmful to an indigenous species larch, the tamarack , killing both young and mature trees. Larches are also vulnerable to Phytophthora ramorum . In late 2009 the disease was first found in Japanese larch trees in
1848-544: Is present on each sister chromatid . A special DNA base sequence in the region of the kinetochores provides, along with special proteins, longer-lasting attachment in this region. The microtubules then pull the chromatids apart toward the centrosomes, so that each daughter cell inherits one set of chromatids. Once the cells have divided, the chromatids are uncoiled and DNA can again be transcribed. In spite of their appearance, chromosomes are structurally highly condensed, which enables these giant DNA structures to be contained within
1925-413: Is significant variation within species. Often there is: Also, variation in karyotype may occur during development from the fertilized egg. The technique of determining the karyotype is usually called karyotyping . Cells can be locked part-way through division (in metaphase) in vitro (in a reaction vial) with colchicine . These cells are then stained, photographed, and arranged into a karyogram , with
2002-440: Is sometimes used in a wider sense to refer to the individualized portions of chromatin in cells, which may or may not be visible under light microscopy. In a narrower sense, 'chromosome' can be used to refer to the individualized portions of chromatin during cell division, which are visible under light microscopy due to high condensation. The word chromosome ( / ˈ k r oʊ m ə ˌ s oʊ m , - ˌ z oʊ m / ) comes from
2079-425: Is the characteristic chromosome complement of a eukaryote species . The preparation and study of karyotypes is part of cytogenetics . Although the replication and transcription of DNA is highly standardized in eukaryotes, the same cannot be said for their karyotypes, which are often highly variable. There may be variation between species in chromosome number and in detailed organization. In some cases, there
2156-429: Is the only natural context in which individual chromosomes are visible with an optical microscope . Mitotic metaphase chromosomes are best described by a linearly organized longitudinally compressed array of consecutive chromatin loops. During mitosis, microtubules grow from centrosomes located at opposite ends of the cell and also attach to the centromere at specialized structures called kinetochores , one of which
2233-522: Is useful in plant identification; for instance in parts of Southern California and the American Southeast , deciduous and evergreen oak species may grow side by side. Periods of leaf fall often coincide with seasons: winter in the case of cool-climate plants or the dry-season in the case of tropical plants, however there are no deciduous species among tree-like monocotyledonous plants, e.g. palms , yuccas , and dracaenas . The hydrangea hirta
2310-626: The English counties of Devon , Cornwall and Somerset , and has since spread to the south-west of Scotland. In August 2010 the disease was found in Japanese larch trees in counties Waterford and Tipperary in Ireland and in 2013 in the Afan Forest Park in south Wales . Laricifomes officinalis is another mushroom found in Europe , North America and northern Asia that causes internal wood rot. It
2387-553: The Greek words χρῶμα ( chroma , "colour") and σῶμα ( soma , "body"), describing the strong staining produced by particular dyes . The term was coined by the German anatomist Heinrich Wilhelm Waldeyer , referring to the term ' chromatin ', which was introduced by Walther Flemming . Some of the early karyological terms have become outdated. For example, 'chromatin' (Flemming 1880) and 'chromosom' (Waldeyer 1888) both ascribe color to
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2464-437: The cell cycle where the cell is not dividing), two types of chromatin can be distinguished: In the early stages of mitosis or meiosis (cell division), the chromatin double helix becomes more and more condensed. They cease to function as accessible genetic material ( transcription stops) and become a compact transportable form. The loops of thirty-nanometer chromatin fibers are thought to fold upon themselves further to form
2541-502: The cytoplasm that contain cellular DNA and play a role in horizontal gene transfer . In prokaryotes and viruses, the DNA is often densely packed and organized; in the case of archaea, by homology to eukaryotic histones, and in the case of bacteria, by histone-like proteins. Bacterial chromosomes tend to be tethered to the plasma membrane of the bacteria. In molecular biology application, this allows for its isolation from plasmid DNA by centrifugation of lysed bacteria and pelleting of
2618-451: The endosymbiotic bacteria Candidatus Hodgkinia cicadicola and Candidatus Tremblaya princeps , to more than 14,000,000 base pairs in the soil-dwelling bacterium Sorangium cellulosum . Some bacteria have more than one chromosome. For instance, Spirochaetes such as Borrelia burgdorferi (causing Lyme disease ), contain a single linear chromosome. Vibrios typically carry two chromosomes of very different size. Genomes of
2695-503: The foliage before they are shed and store them in the form of proteins in the vacuoles of parenchyma cells in the roots and the inner bark. In the spring, these proteins are used as a nitrogen source during the growth of new leaves or flowers. Plants with deciduous foliage have advantages and disadvantages compared to plants with evergreen foliage. Since deciduous plants lose their leaves to conserve water or to better survive winter weather conditions, they must regrow new foliage during
2772-563: The 16 chromosomes of yeast were fused into one giant chromosome, it was found that the cells were still viable with only somewhat reduced growth rates. The tables below give the total number of chromosomes (including sex chromosomes) in a cell nucleus for various eukaryotes. Most are diploid , such as humans who have 22 different types of autosomes —each present as two homologous pairs—and two sex chromosomes , giving 46 chromosomes in total. Some other organisms have more than two copies of their chromosome types, for example bread wheat which
2849-423: The DNA molecule to maintain its integrity. These eukaryotic chromosomes display a complex three-dimensional structure that has a significant role in transcriptional regulation . Normally, chromosomes are visible under a light microscope only during the metaphase of cell division , where all chromosomes are aligned in the center of the cell in their condensed form. Before this stage occurs, each chromosome
2926-834: The Himalayas, Europe and for cultivation purposes in Oceania. They have formed under climatic conditions which have great seasonable temperature variability. Growth occurs during warm summers, leaf drop in autumn, and dormancy during cold winters. These seasonally distinctive communities have diverse life forms that are impacted greatly by the seasonality of their climate, mainly temperature and precipitation rates. These varying and regionally different ecological conditions produce distinctive forest plant communities in different regions. Tropical and subtropical deciduous forest biomes have developed in response not to seasonal temperature variations but to seasonal rainfall patterns. During prolonged dry periods
3003-537: The autumn. The English name larch ultimately derives from the Latin "larigna", named after the ancient settlement of Larignum. The story of its naming was preserved by Vitruvius : It is worth while to know how this wood was discovered. The divine Caesar, being with his army in the neighbourhood of the Alps, and having ordered the towns to furnish supplies, the inhabitants of a fortified stronghold there, called Larignum, trusting in
3080-428: The bald cypresses in the genus Taxodium . The male flowers (small cones) are orange-yellowish and fall after pollination. The female flowers (or cones ) of larches are erect, small, 1–9 cm ( 1 ⁄ 2 – 3 + 1 ⁄ 2 in) long, green or purple, brown in ripening and lignify (called now strobilus ) 5–8 months after pollination; in about half the species the bract scales are long and visible, and in
3157-423: The cell's nucleus. Each chromosome has one centromere , with one or two arms projecting from the centromere, although, under most circumstances, these arms are not visible as such. In addition, most eukaryotes have a small circular mitochondrial genome , and some eukaryotes may have additional small circular or linear cytoplasmic chromosomes. In the nuclear chromosomes of eukaryotes, the uncondensed DNA exists in
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3234-507: The closest living relatives to modern humans, have 48 chromosomes as do the other great apes : in humans two chromosomes fused to form chromosome 2 . Chromosomal aberrations are disruptions in the normal chromosomal content of a cell. They can cause genetic conditions in humans, such as Down syndrome , although most aberrations have little to no effect. Some chromosome abnormalities do not cause disease in carriers, such as translocations , or chromosomal inversions , although they may lead to
3311-406: The compact metaphase chromosomes of mitotic cells. The DNA is thus condensed about ten-thousand-fold. The chromosome scaffold , which is made of proteins such as condensin , TOP2A and KIF4 , plays an important role in holding the chromatin into compact chromosomes. Loops of thirty-nanometer structure further condense with scaffold into higher order structures. This highly compact form makes
3388-428: The earliest trees to lose their leaves in the fall. In sub-Arctic climates such as Alaska , leaves begin turning colors as early as August. However, for most temperate regions it takes place in late September through early November and in subtropical climates such as the southern US, it may be November into December. Leaf drop or abscission involves complex physiological signals and changes within plants. When leafout
3465-677: The fall months and the Western United States as it has more evergreen and fewer deciduous plants, combined with the West Coast and its maritime climate. ( See also : Autumn leaf color ) Most of the Southern Hemisphere lacks deciduous plants due to its milder winters and smaller landmass, most of which is nearer the equator with only far southern South America and the southern island of New Zealand producing distinct fall colors. The beginnings of leaf drop starts when an abscission layer
3542-425: The fields of horticulture and botany , the term deciduous ( / d ɪ ˈ s ɪ dʒ u . ə s / ) means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves , usually in the autumn ; to the shedding of petals , after flowering; and to the shedding of ripe fruit . The antonym of deciduous in the botanical sense is evergreen . Generally,
3619-426: The foliage is dropped to conserve water and prevent death from drought. Leaf drop is not seasonally dependent as it is in temperate climates. It can occur any time of year and varies by region of the world. Even within a small local area there can be variations in the timing and duration of leaf drop; different sides of the same mountain and areas that have high water tables or areas along streams and rivers can produce
3696-473: The genus Burkholderia carry one, two, or three chromosomes. Prokaryotic chromosomes have less sequence-based structure than eukaryotes. Bacteria typically have a one-point (the origin of replication ) from which replication starts, whereas some archaea contain multiple replication origins. The genes in prokaryotes are often organized in operons and do not usually contain introns , unlike eukaryotes. Prokaryotes do not possess nuclei. Instead, their DNA
3773-457: The genus, with a primary division into North American and Eurasian species, and a secondary division of the Eurasian into northern short-bracted species and southern long-bracted species; there is some dispute over the position of Larix sibirica , a short-bracted species which is placed in the short-bracted group by some of the studies and the long-bracted group by others. The genus Larix belongs to
3850-521: The ground, and historically was used as posts and in fencing. However, European Standard EN 350-2 lists larch as slightly to moderately durable; this would make it unsuitable for ground contact use without preservative in temperate climates, and would give it a limited life as external cladding without coatings. The hybrid Dunkeld larch is widely grown as a timber crop in Northern Europe , valued for its fast growth and disease resistance. Larch on oak
3927-417: The humid maritime climate and lower overall species diversity . It is also a factor that the continental United States and southern Canada are at a lower latitude than northern Europe, so the sun during the fall months is higher and stronger. This combination of strong sun and cool temperatures leads to more intense fall colors. The Southern United States also has poor fall colors due to warm temperatures during
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#17330856523624004-583: The independent work of Boveri and Sutton (both around 1902) by naming the chromosome theory of inheritance the ' Boveri–Sutton chromosome theory ' (sometimes known as the 'Sutton–Boveri chromosome theory'). Ernst Mayr remarks that the theory was hotly contested by some famous geneticists, including William Bateson , Wilhelm Johannsen , Richard Goldschmidt and T.H. Morgan , all of a rather dogmatic mindset. Eventually, absolute proof came from chromosome maps in Morgan's own laboratory. The number of human chromosomes
4081-461: The individual chromosomes visible, and they form the classic four-arm structure, a pair of sister chromatids attached to each other at the centromere . The shorter arms are called p arms (from the French petit , small) and the longer arms are called q arms ( q follows p in the Latin alphabet; q-g "grande"; alternatively it is sometimes said q is short for queue meaning tail in French ). This
4158-677: The kind under discussion, of which there are very great numbers in that vicinity. And so, as that stronghold was called Larignum, the wood was called larch. The tallest species, Larix occidentalis , can reach 50 to 60 m (165 to 195 ft). The larch's tree crown is sparse and the branches are brought horizontal to the stem, even if some species have them characteristically pendulous . Larch shoots are dimorphic, with leaves borne singly on long shoots typically 10 to 50 cm (4 to 20 in) long and bearing several buds , and in dense clusters of 20–50 needles on short shoots only 1–2 mm ( 1 ⁄ 32 – 3 ⁄ 32 in) long with only
4235-507: The leaves are shed at the same time. Plants that are intermediate may be called semi-deciduous ; they lose old foliage as new growth begins. Other plants are semi-evergreen and lose their leaves before the next growing season, retaining some during winter or dry periods. Many deciduous plants flower during the period when they are leafless, as this increases the effectiveness of pollination . The absence of leaves improves wind transmission of pollen for wind-pollinated plants and increases
4312-526: The leaves. Rather, they are produced in the foliage in late summer, when sugars are trapped in the leaves after the process of abscission begins. Parts of the world that have showy displays of bright autumn colors are limited to locations where days become short and nights are cool. The New England region of the United States and southeastern Canada tend to produce particularly good autumn colors for this reason, with Europe producing generally poorer colors due to
4389-494: The matching chromosomes of father and mother can exchange small parts of themselves ( crossover ) and thus create new chromosomes that are not inherited solely from either parent. When a male and a female gamete merge during fertilization , a new diploid organism is formed. Some animal and plant species are polyploid [Xn], having more than two sets of homologous chromosomes . Important crops such as tobacco or wheat are often polyploid, compared to their ancestral species. Wheat has
4466-429: The membranes (and the attached DNA). Prokaryotic chromosomes and plasmids are, like eukaryotic DNA, generally supercoiled . The DNA must first be released into its relaxed state for access for transcription , regulation, and replication . Each eukaryotic chromosome consists of a long linear DNA molecule associated with proteins , forming a compact complex of proteins and DNA called chromatin . Chromatin contains
4543-403: The natural strength of their defences, refused to obey his command. So the general ordered his forces to the assault. In front of the gate of this stronghold there was a tower, made of beams of this wood laid in alternating directions at right angles to each other, like a funeral pyre, and built high, so that they could drive off an attacking party by throwing stakes and stones from the top. When it
4620-783: The next suitable growing season; this uses resources which evergreens do not need to expend. Evergreens suffer greater water loss during the winter and they also can experience greater predation pressure , especially when small. Deciduous trees experience much less branch and trunk breakage from glaze ice storms when leafless, and plants can reduce water loss due to the reduction in availability of liquid water during cold winter days. Losing leaves in winter may reduce damage from insects; repairing leaves and keeping them functional may be more costly than just losing and regrowing them. Removing leaves also reduces cavitation which can damage xylem vessels in plants. This then allows deciduous plants to have xylem vessels with larger diameters and therefore
4697-468: The others, short and hidden between the seed scales. Those native to northern regions have small cones ( 1–3 cm or 1 ⁄ 2 –1 in) with short bracts, with more southerly species tending to have longer cones ( 3–9 cm or 1 + 1 ⁄ 4 – 3 + 1 ⁄ 2 in), often with exserted bracts, with the longest cones and bracts produced by the southernmost species, in the Himalayas. The seeds are winged. The larches are streamlined trees,
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#17330856523624774-440: The past, the cone bract length was often used to divide the larches into two sections (sect. Larix with short bracts, and sect. Multiserialis with long bracts), but genetic evidence does not support this division, pointing instead to a genetic divide between Old World and New World species, with the cone and bract size being merely adaptations to climatic conditions. More recent genetic studies have proposed three groups within
4851-469: The plant, the cells of the abscission layer remain connected; in autumn, or when under stress, the auxin flow from the leaf decreases or stops, triggering cellular elongation within the abscission layer. The elongation of these cells breaks the connection between the different cell layers, allowing the leaf to break away from the plant. It also forms a layer that seals the break, so the plant does not lose sap. Some trees, particularly oaks and beeches, exhibit
4928-486: The risk of aneuploid spermatozoa. In particular, risk of aneuploidy is increased by tobacco smoking, and occupational exposure to benzene, insecticides, and perfluorinated compounds. Increased aneuploidy is often associated with increased DNA damage in spermatozoa. The number of chromosomes in eukaryotes is highly variable. It is possible for chromosomes to fuse or break and thus evolve into novel karyotypes. Chromosomes can also be fused artificially. For example, when
5005-591: The root system is broad and deep and the bark is finely cracked and wrinkled in irregular plaques. The wood is bicolor, with salmon pink heartwood and yellowish white sapwood. The chromosome number is 2n = 24, similar to that of most of the other trees of the family Pinaceae . The genus Larix is present in all the temperate-cold zones of the northern hemisphere , from North America to northern Siberia passing through Europe , mountainous China and Japan . The larches are important forest trees of Russia , Central Europe , United States and Canada . They require
5082-438: The same in all body cells. However, asexual species can be either haploid or diploid. Sexually reproducing species have somatic cells (body cells) that are diploid [2n], having two sets of chromosomes (23 pairs in humans), one set from the mother and one from the father. Gametes (reproductive cells) are haploid [n], having one set of chromosomes. Gametes are produced by meiosis of a diploid germline cell, during which
5159-594: The set of chromosomes arranged, autosomes in order of length, and sex chromosomes (here X/Y) at the end. Like many sexually reproducing species, humans have special gonosomes (sex chromosomes, in contrast to autosomes ). These are XX in females and XY in males. Investigation into the human karyotype took many years to settle the most basic question: How many chromosomes does a normal diploid human cell contain? In 1912, Hans von Winiwarter reported 47 chromosomes in spermatogonia and 48 in oogonia , concluding an XX/XO sex determination mechanism . In 1922, Painter
5236-651: The subfamily Laricoideae , which also includes the genera Pseudotsuga and Cathaya . There are ten accepted species of larch and one accepted hybrid, subdivided on the basis of the most recent phylogenetic investigations: Most if not all of the species can be hybridised in cultivation. Selected hybrids include: The hybrid Larix × marschlinsii , the Dunkeld larch, is an artificial hybrid L. decidua × L. sibirica that arose more or less simultaneously in Switzerland and Scotland. Larix × stenophylla Sukaczev
5313-591: The term "deciduous" means "the dropping of a part that is no longer needed or useful" and the "falling away after its purpose is finished". In plants, it is the result of natural processes. "Deciduous" has a similar meaning when referring to animal parts, such as deciduous antlers in deer , deciduous teeth (baby teeth) in some mammals (including humans); or decidua , the uterine lining that sheds off after birth. In botany and horticulture , deciduous plants , including trees , shrubs and herbaceous perennials, are those that lose all of their leaves for part of
5390-459: The vast majority of the DNA in an organism, but a small amount inherited maternally can be found in the mitochondria . It is present in most cells , with a few exceptions, for example, red blood cells . Histones are responsible for the first and most basic unit of chromosome organization, the nucleosome . Eukaryotes ( cells with nuclei such as those found in plants, fungi, and animals) possess multiple large linear chromosomes contained in
5467-702: The visibility of the flowers to insects in insect-pollinated plants. This strategy is not without risks, as the flowers can be damaged by frost or, in dry season regions, result in water stress on the plant. Spring leafout and fall leaf drop are triggered by a combination of daylight and air temperatures. The exact conditions required will vary with the species, but generally more cold-tolerant genera such as Salix will leaf-out earlier and lose their leaves later, while genera such as Fraxinus and Juglans can only grow in warm, frost-free conditions so they need at least 13 hours of daylight and air temperatures of around 70 °F (21 °C) to leaf out. They will be among
5544-402: The whole pile had fallen. But when the fire had burned itself out and subsided, and the tower appeared to view entirely uninjured, Caesar in amazement gave orders that they should be surrounded with a palisade, built beyond the range of missiles. So the townspeople were frightened into surrendering, and were then asked where that wood came from which was not harmed by fire. They pointed to trees of
5621-501: The year. This process is called abscission . In some cases leaf loss coincides with winter—namely in temperate or polar climates . In other parts of the world, including tropical, subtropical, and arid regions, plants lose their leaves during the dry season or other seasons, depending on variations in rainfall . The converse of deciduous is evergreen , where foliage is shed on a different schedule from deciduous plants, therefore appearing to remain green year round because not all
5698-440: Was not certain whether the diploid number of man is 46 or 48, at first favouring 46. He revised his opinion later from 46 to 48, and he correctly insisted on humans having an XX/XY system. New techniques were needed to definitively solve the problem: It took until 1954 before the human diploid number was confirmed as 46. Considering the techniques of Winiwarter and Painter, their results were quite remarkable. Chimpanzees ,
5775-412: Was observed that they had no other missiles than stakes, and that these could not be hurled very far from the wall on account of the weight, orders were given to approach and to throw bundles of brushwood and lighted torches at this outwork. These the soldiers soon got together. The flames soon kindled the brushwood which lay about that wooden structure and, rising towards heaven, made everybody think that
5852-544: Was published by Painter in 1923. By inspection through a microscope, he counted 24 pairs of chromosomes, giving 48 in total. His error was copied by others, and it was not until 1956 that the true number (46) was determined by Indonesian-born cytogeneticist Joe Hin Tjio . The prokaryotes – bacteria and archaea – typically have a single circular chromosome . The chromosomes of most bacteria (also called genophores ), can range in size from only 130,000 base pairs in
5929-401: Was the traditional construction method for Scottish fishing boats in the 19th century. Larch has also been used in herbal medicine ; see Bach flower remedies and Arabinogalactan for details. Often, in Eurasian shamanism , the " world tree " is depicted as specifically a larch tree. Planted on borders with birch , both tree species were used in pagan cremations. Deciduous In
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