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114-581: The origins of the breed are obscure. According to a genetic study of "Spanish Celtic horse breeds", the Mallorquín and Menorquín are connected to the now extinct Catalan horse, itself the result of introgression of populations with strong African genetic influence into an original population of Celtic horses introduced to the Iberian peninsula by the Celts around the eighth century BC. The study showed clear grouping of

228-429: A helical structure (i.e., shaped like a corkscrew). Their double-helix model had two strands of DNA with the nucleotides pointing inward, each matching a complementary nucleotide on the other strand to form what look like rungs on a twisted ladder. This structure showed that genetic information exists in the sequence of nucleotides on each strand of DNA. The structure also suggested a simple method for replication : if

342-534: A sexual process for transferring DNA from one cell to another cell (usually of the same species). Transformation requires the action of numerous bacterial gene products , and its primary adaptive function appears to be repair of DNA damages in the recipient cell. The diploid nature of chromosomes allows for genes on different chromosomes to assort independently or be separated from their homologous pair during sexual reproduction wherein haploid gametes are formed. In this way new combinations of genes can occur in

456-573: A DNA molecule. In 1983, Kary Banks Mullis developed the polymerase chain reaction , providing a quick way to isolate and amplify a specific section of DNA from a mixture. The efforts of the Human Genome Project , Department of Energy, NIH, and parallel private efforts by Celera Genomics led to the sequencing of the human genome in 2003. At its most fundamental level, inheritance in organisms occurs by passing discrete heritable units, called genes , from parents to offspring. This property

570-520: A Nobel Prize in Physiology. In the early 1900s, Gregor Mendel , who became known as one of the fathers of genetics , made great contributions to the field of genetics through his various experiments with pea plants where he was able to discover the principles of inheritance such as recessive and dominant traits, without knowing what genes where composed of. In the mid 19th century, anatomist Walther Flemming, discovered what we now know as chromosomes and

684-401: A certain phenotype . In a genetic screen , random mutations are generated with mutagens (chemicals or radiation) or transposons and individuals are screened for the specific phenotype. Often, a secondary assay in the form of a selection may follow mutagenesis where the desired phenotype is difficult to observe, for example in bacteria or cell cultures. The cells may be transformed using

798-486: A complex trait is called heritability . Measurement of the heritability of a trait is relative—in a more variable environment, the environment has a bigger influence on the total variation of the trait. For example, human height is a trait with complex causes. It has a heritability of 89% in the United States. In Nigeria, however, where people experience a more variable access to good nutrition and health care , height has

912-483: A different parent. Many species have so-called sex chromosomes that determine the sex of each organism. In humans and many other animals, the Y chromosome contains the gene that triggers the development of the specifically male characteristics. In evolution, this chromosome has lost most of its content and also most of its genes, while the X chromosome is similar to the other chromosomes and contains many genes. This being said, Mary Frances Lyon discovered that there

1026-546: A diploid cell with paired chromosomes. Diploid organisms form haploids by dividing, without replicating their DNA, to create daughter cells that randomly inherit one of each pair of chromosomes. Most animals and many plants are diploid for most of their lifespan, with the haploid form reduced to single cell gametes such as sperm or eggs . Although they do not use the haploid/diploid method of sexual reproduction, bacteria have many methods of acquiring new genetic information. Some bacteria can undergo conjugation , transferring

1140-454: A disease they are afflicted with and potentially allow for more individualized treatment approaches which could be more effective. For example, certain genetic variations in individuals could make them more receptive to a particular drug while other could have a higher risk of adverse reaction to treatments. So this information would allow researchers and clinicals to make the most informed decisions about treatment efficacy for patients rather than

1254-426: A gene for antibiotic resistance or a fluorescent reporter so that the mutants with the desired phenotype are selected from the non-mutants. Mutants exhibiting the phenotype of interest are isolated and a complementation test may be performed to determine if the phenotype results from more than one gene. The mutant genes are then characterized as dominant (resulting in a gain of function), recessive (showing

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1368-429: A gene is used to produce a specific amino acid sequence . This process begins with the production of an RNA molecule with a sequence matching the gene's DNA sequence, a process called transcription . This messenger RNA molecule then serves to produce a corresponding amino acid sequence through a process called translation . Each group of three nucleotides in the sequence, called a codon , corresponds either to one of

1482-482: A heritability of only 62%. The molecular basis for genes is deoxyribonucleic acid (DNA). DNA is composed of deoxyribose (sugar molecule), a phosphate group, and a base (amine group). There are four types of bases: adenine (A), cytosine (C), guanine (G), and thymine (T). The phosphates make phosphodiester bonds with the sugars to make long phosphate-sugar backbones. Bases specifically pair together (T&A, C&G) between two backbones and make like rungs on

1596-435: A higher body temperature. In a low-temperature environment, however, the protein's structure is stable and produces dark-hair pigment normally. The protein remains functional in areas of skin that are colder—such as its legs, ears, tail, and face—so the cat has dark hair at its extremities. Environment plays a major role in effects of the human genetic disease phenylketonuria . The mutation that causes phenylketonuria disrupts

1710-435: A knockdown. Knockdown may also be achieved by RNA interference (RNAi). Alternatively, genes may be substituted into an organism's genome (also known as a transgene ) to create a gene knock-in and result in a gain of function by the host. Although these techniques have some inherent bias regarding the decision to link a phenotype to a particular function, it is much faster in terms of production than forward genetics because

1824-503: A ladder. The bases, phosphates, and sugars together make a nucleotide that connects to make long chains of DNA. Genetic information exists in the sequence of these nucleotides, and genes exist as stretches of sequence along the DNA chain. These chains coil into a double a-helix structure and wrap around proteins called Histones which provide the structural support. DNA wrapped around these histones are called chromosomes. Viruses sometimes use

1938-505: A living cell or organism may increase or decrease gene transcription. A classic example is two seeds of genetically identical corn, one placed in a temperate climate and one in an arid climate (lacking sufficient waterfall or rain). While the average height the two corn stalks could grow to is genetically determined, the one in the arid climate only grows to half the height of the one in the temperate climate due to lack of water and nutrients in its environment. The word genetics stems from

2052-422: A loss of function), or epistatic (the mutant gene masks the phenotype of another gene). Finally, the location and specific nature of the mutation is mapped via sequencing . Forward genetics is an unbiased approach and often leads to many unanticipated discoveries, but may be costly and time consuming. Model organisms like the nematode worm Caenorhabditis elegans , the fruit fly Drosophila melanogaster , and

2166-438: A mistaken alignment; this makes some regions in genomes more prone to mutating in this way. These errors create large structural changes in DNA sequence— duplications , inversions , deletions of entire regions—or the accidental exchange of whole parts of sequences between different chromosomes, chromosomal translocation . Molecular genetics Molecular genetics is a branch of biology that addresses how differences in

2280-539: A particular location on the genome that are used as genetic marker. Researchers can analyze these microsatellites in techniques such DNA fingerprinting and paternity testing since these repeats are highly unique to individuals/families. a can also be used in constructing genetic maps and to studying genetic linkage to locate the gene or mutation responsible for specific trait or disease. Microsatellites can also be applied to population genetics to study comparisons between groups. Genome-wide association studies (GWAS) are

2394-456: A phenotype involves studying identical and fraternal twins , or other siblings of multiple births . Identical siblings are genetically the same since they come from the same zygote. Meanwhile, fraternal twins are as genetically different from one another as normal siblings. By comparing how often a certain disorder occurs in a pair of identical twins to how often it occurs in a pair of fraternal twins, scientists can determine whether that disorder

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2508-403: A series of genes can be combined to form a linear linkage map that roughly describes the arrangement of the genes along the chromosome. Genes express their functional effect through the production of proteins, which are molecules responsible for most functions in the cell. Proteins are made up of one or more polypeptide chains, each composed of a sequence of amino acids . The DNA sequence of

2622-457: A single parent. Offspring that are genetically identical to their parents are called clones . Eukaryotic organisms often use sexual reproduction to generate offspring that contain a mixture of genetic material inherited from two different parents. The process of sexual reproduction alternates between forms that contain single copies of the genome ( haploid ) and double copies ( diploid ). Haploid cells fuse and combine genetic material to create

2736-448: A small circular piece of DNA to another bacterium. Bacteria can also take up raw DNA fragments found in the environment and integrate them into their genomes, a phenomenon known as transformation . These processes result in horizontal gene transfer , transmitting fragments of genetic information between organisms that would be otherwise unrelated. Natural bacterial transformation occurs in many bacterial species, and can be regarded as

2850-400: A smooth blend of traits from their parents. Mendel's work provided examples where traits were definitely not blended after hybridization, showing that traits are produced by combinations of distinct genes rather than a continuous blend. Blending of traits in the progeny is now explained by the action of multiple genes with quantitative effects . Another theory that had some support at that time

2964-453: A technique that relies on single nucleotide polymorphisms ( SNPs ) to study genetic variations in populations that can be associated with a particular disease. The Human Genome Project mapped the entire human genome and has made this approach more readily available and cost effective for researchers to implement. In order to conduct a GWAS researchers use two groups, one group that has the disease researchers are studying and another that acts as

3078-457: A tiny quantity of DNA from a crime scene can be extracted and replicated many times to provide a sufficient amount of material for analysis. Gel electrophoresis allows the DNA sequence to be separated based on size, and the pattern that is derived is known as DNA fingerprinting and is unique to each individual. This combination of molecular genetic techniques allows a simple DNA sequence to be extracted, amplified, analyzed and compared with others and

3192-448: A transition of heredity from its status as myth to that of a scientific discipline, by providing a fundamental theoretical basis for genetics in the twentieth century. Other theories of inheritance preceded Mendel's work. A popular theory during the 19th century, and implied by Charles Darwin 's 1859 On the Origin of Species , was blending inheritance : the idea that individuals inherit

3306-412: A unique three-dimensional structure for that protein, and the three-dimensional structures of proteins are related to their functions. Some are simple structural molecules, like the fibers formed by the protein collagen . Proteins can bind to other proteins and simple molecules, sometimes acting as enzymes by facilitating chemical reactions within the bound molecules (without changing the structure of

3420-400: A variety of hereditary characteristics that replicate and remain active throughout generations. While haploid organisms have only one copy of each chromosome, most animals and many plants are diploid , containing two of each chromosome and thus two copies of every gene. The two alleles for a gene are located on identical loci of the two homologous chromosomes , each allele inherited from

3534-702: Is 1.52 metres (15.0 hands ) for males and 1.48 m (14.2 h) for females. It has an upright mane, short, thick, but arched neck, a head with a convex profile but refined bone structure. Its conformation relates to that of the Andalusian horse This breed is used by the local population only as a riding horse ; farm work in the islands was traditionally done by the Balearic donkey . Mallorquín mares were traditionally bred to imported stallions, usually of French Trotter or Orlov Trotter breed, to produce Trotador Español, " Spanish Trotter ", horses. Approximately 85% of

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3648-488: Is X-chromosome inactivation during reproduction to avoid passing on twice as many genes to the offspring. Lyon's discovery led to the discovery of X-linked diseases. When cells divide, their full genome is copied and each daughter cell inherits one copy. This process, called mitosis , is the simplest form of reproduction and is the basis for asexual reproduction. Asexual reproduction can also occur in multicellular organisms, producing offspring that inherit their genome from

3762-425: Is a somewhat ambiguous definition of what is referred to as a gene. Trait inheritance and molecular inheritance mechanisms of genes are still primary principles of genetics in the 21st century, but modern genetics has expanded to study the function and behavior of genes. Gene structure and function, variation, and distribution are studied within the context of the cell , the organism (e.g. dominance ), and within

3876-481: Is an emerging field of science, and researcher are able to leverage molecular genetic technology to modify the DNA of organisms and create genetically modified and enhanced organisms for industrial, agricultural and medical purposes. This can be done through genome editing techniques, which can involve modifying base pairings in a DNA sequence, or adding and deleting certain regions of DNA. Gene editing allows scientists to alter/edit an organism's DNA. One way to due this

3990-480: Is an essential component to the field of molecular genetics; it is the basis of how DNA is able to store genetic information, pass it on, and be in a format that can be read and translated. DNA is a double stranded molecule, with each strand oriented in an antiparallel fashion. Nucleotides are the building blocks of DNA, each composed of a sugar molecule, a phosphate group and one of four nitrogenous bases: adenine, guanine, cytosine, and thymine. A single strand of DNA

4104-478: Is caused by genetic or postnatal environmental factors. One famous example involved the study of the Genain quadruplets , who were identical quadruplets all diagnosed with schizophrenia . The genome of a given organism contains thousands of genes, but not all these genes need to be active at any given moment. A gene is expressed when it is being transcribed into mRNA and there exist many cellular methods of controlling

4218-455: Is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C)." These rules, known as Chargaff's rules, helped to understand of molecular genetics. In 1953 Francis Crick and James Watson, building upon the X-ray crystallography work done by Rosalind Franklin and Maurice Wilkins, were able to derive the 3-D double helix structure of DNA. The phage group

4332-592: Is held together by covalent bonds, while the two antiparallel strands are held together by hydrogen bonds between the nucleotide bases. Adenine binds with thymine and cytosine binds with guanine. It is these four base sequences that form the genetic code for all biological life and contains the information for all the proteins the organism will be able to synthesize. Its unique structure allows DNA to store and pass on biological information across generations during cell division . At cell division, cells must be able to copy its genome and pass it on to daughter cells. This

4446-424: Is possible due to the double-stranded structure of DNA because one strand is complementary to its partner strand, and therefore each of these strands can act as a template strand for the formation of a new complementary strand. This is why the process of DNA replication is known as a semiconservative process. Forward genetics is a molecular genetics technique used to identify genes or genetic mutations that produce

4560-409: Is redundant, meaning multiple combinations of these base pairs (which are read in triplicate) produce the same amino acid. Proteomics and genomics are fields in biology that come out of the study of molecular genetics and the central dogma. An organism's genome is made up by its entire set of DNA and is responsible for its genetic traits, function and development. The composition of DNA itself

4674-441: Is responsible for the development of structures within multicellular organisms, these patterns arise from the complex interactions between many cells. Within eukaryotes , there exist structural features of chromatin that influence the transcription of genes, often in the form of modifications to DNA and chromatin that are stably inherited by daughter cells. These features are called " epigenetic " because they exist "on top" of

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4788-465: Is specified by the nucleotide sequence of the gene determining the protein.  The isolation of a restriction endonuclease in E. coli by Arber and Linn in 1969 opened the field of genetic engineering .  Restriction enzymes were used to linearize DNA for separation by electrophoresis and Southern blotting allowed for the identification of specific DNA segments via hybridization probes . In 1971, Berg utilized restriction enzymes to create

4902-472: Is the genetic material of bacteria. Bacterial transformation is often induced by conditions of stress, and the function of transformation appears to be repair of genomic damage . In 1950, Erwin Chargaff derived rules that offered evidence of DNA being the genetic material of life. These were "1) that the base composition of DNA varies between species and 2) in natural DNA molecules, the amount of adenine (A)

5016-497: Is the physical basis for inheritance: DNA replication duplicates the genetic information by splitting the strands and using each strand as a template for synthesis of a new partner strand. Genes are arranged linearly along long chains of DNA base-pair sequences. In bacteria , each cell usually contains a single circular genophore , while eukaryotic organisms (such as plants and animals) have their DNA arranged in multiple linear chromosomes. These DNA strands are often extremely long;

5130-694: Is the same as that which Mendel published. In his third law, he developed the basic principles of mutation (he can be considered a forerunner of Hugo de Vries ). Festetics argued that changes observed in the generation of farm animals, plants, and humans are the result of scientific laws. Festetics empirically deduced that organisms inherit their characteristics, not acquire them. He recognized recessive traits and inherent variation by postulating that traits of past generations could reappear later, and organisms could produce progeny with different attributes. These observations represent an important prelude to Mendel's theory of particulate inheritance insofar as it features

5244-469: Is through the technique Crispr/Cas9 , which was adapted from the genome immune defense that is naturally occurring in bacteria. This technique relies on the protein Cas9 which allows scientists to make a cut in strands of DNA at a specific location, and it uses a specialized RNA guide sequence to ensure the cut is made in the proper location in the genome. Then scientists use DNAs repair pathways to induce changes in

5358-568: Is transcribed into RNA, and RNA is translated into proteins. Along with the central dogma, the genetic code is used in understanding how RNA is translated into proteins. Replication of DNA and transcription from DNA to mRNA occurs in the nucleus while translation from RNA to proteins occurs in the ribosome . The genetic code is made of four interchangeable parts othe DNA molecules, called "bases": adenine, cytosine, uracil (in RNA; thymine in DNA), and guanine and

5472-461: Is vital to organisms' evolution . Gregor Mendel , a Moravian Augustinian friar working in the 19th century in Brno , was the first to study genetics scientifically. Mendel studied "trait inheritance", patterns in the way traits are handed down from parents to offspring over time. He observed that organisms (pea plants) inherit traits by way of discrete "units of inheritance". This term, still used today,

5586-479: The Blue-eyed Mary ( Omphalodes verna ), for example, there exists a gene with alleles that determine the color of flowers: blue or magenta. Another gene, however, controls whether the flowers have color at all or are white. When a plant has two copies of this white allele, its flowers are white—regardless of whether the first gene has blue or magenta alleles. This interaction between genes is called epistasis , with

5700-413: The ancient Greek γενετικός genetikos meaning "genitive"/"generative", which in turn derives from γένεσις genesis meaning "origin". The observation that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding . The modern science of genetics, seeking to understand this process, began with

5814-415: The neutral theory of molecular evolution through publishing the nearly neutral theory of molecular evolution . In this theory, Ohta stressed the importance of natural selection and the environment to the rate at which genetic evolution occurs. One important development was chain-termination DNA sequencing in 1977 by Frederick Sanger . This technology allows scientists to read the nucleotide sequence of

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5928-421: The DNA sequence and retain inheritance from one cell generation to the next. Because of epigenetic features, different cell types grown within the same medium can retain very different properties. Although epigenetic features are generally dynamic over the course of development, some, like the phenomenon of paramutation , have multigenerational inheritance and exist as rare exceptions to the general rule of DNA as

6042-624: The F1 offspring mate with each other, the offspring are called the "F2" (second filial) generation. One of the common diagrams used to predict the result of cross-breeding is the Punnett square . When studying human genetic diseases, geneticists often use pedigree charts to represent the inheritance of traits. These charts map the inheritance of a trait in a family tree. Organisms have thousands of genes, and in sexually reproducing organisms these genes generally assort independently of each other. This means that

6156-496: The Greek word genesis —γένεσις, "origin", predates the noun and was first used in a biological sense in 1860. Bateson both acted as a mentor and was aided significantly by the work of other scientists from Newnham College at Cambridge, specifically the work of Becky Saunders , Nora Darwin Barlow , and Muriel Wheldale Onslow . Bateson popularized the usage of the word genetics to describe

6270-539: The Spanish Trotter population is in Mallorca; however, genetic study has found little recent influence of the Mallorquín on the Spanish Trotter breed. They were also much used in the production of mules . Genetics This is an accepted version of this page Genetics is the study of genes , genetic variation , and heredity in organisms . It is an important branch in biology because heredity

6384-448: The ability of the body to break down the amino acid phenylalanine , causing a toxic build-up of an intermediate molecule that, in turn, causes severe symptoms of progressive intellectual disability and seizures. However, if someone with the phenylketonuria mutation follows a strict diet that avoids this amino acid, they remain normal and healthy. A common method for determining how genes and environment ("nature and nurture") contribute to

6498-444: The adaptive function of repair of DNA damages. The first cytological demonstration of crossing over was performed by Harriet Creighton and Barbara McClintock in 1931. Their research and experiments on corn provided cytological evidence for the genetic theory that linked genes on paired chromosomes do in fact exchange places from one homolog to the other. The probability of chromosomal crossover occurring between two given points on

6612-473: The application of molecular genetic techniques, genomics is being studied in many model organisms and data is being collected in computer databases like NCBI and Ensembl . The computer analysis and comparison of genes within and between different species is called bioinformatics , and links genetic mutations on an evolutionary scale. The central dogma plays a key role in the study of molecular genetics. The central dogma states that DNA replicates itself, DNA

6726-440: The basis for inheritance. During the process of DNA replication, errors occasionally occur in the polymerization of the second strand. These errors, called mutations, can affect the phenotype of an organism, especially if they occur within the protein coding sequence of a gene. Error rates are usually very low—1 error in every 10–100 million bases—due to the "proofreading" ability of DNA polymerases . Processes that increase

6840-406: The blueprint for life and breakthroughs in molecular genetics research came from the combined works of many scientists. In 1869, chemist Johann Friedrich Miescher , who was researching the composition of white blood cells, discovered and isolated a new molecule that he named nuclein from the cell nucleus, which would ultimately be the first discovery of the molecule DNA that was later determined to be

6954-404: The cat plays the role of the environment. The cat's genes code for dark hair, thus the hair-producing cells in the cat make cellular proteins resulting in dark hair. But these dark hair-producing proteins are sensitive to temperature (i.e. have a mutation causing temperature-sensitivity) and denature in higher-temperature environments, failing to produce dark-hair pigment in areas where the cat has

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7068-429: The cell, these genes for tryptophan synthesis are no longer needed. The presence of tryptophan directly affects the activity of the genes—tryptophan molecules bind to the tryptophan repressor (a transcription factor), changing the repressor's structure such that the repressor binds to the genes. The tryptophan repressor blocks the transcription and expression of the genes, thereby creating negative feedback regulation of

7182-421: The chromosome is related to the distance between the points. For an arbitrarily long distance, the probability of crossover is high enough that the inheritance of the genes is effectively uncorrelated. For genes that are closer together, however, the lower probability of crossover means that the genes demonstrate genetic linkage; alleles for the two genes tend to be inherited together. The amounts of linkage between

7296-422: The combined DNA sequences of all chromosomes) is called the genome . DNA is most often found in the nucleus of cells, but Ruth Sager helped in the discovery of nonchromosomal genes found outside of the nucleus. In plants, these are often found in the chloroplasts and in other organisms, in the mitochondria. These nonchromosomal genes can still be passed on by either partner in sexual reproduction and they control

7410-486: The context of a population. Genetics has given rise to a number of subfields, including molecular genetics , epigenetics , and population genetics . Organisms studied within the broad field span the domains of life ( archaea , bacteria , and eukarya ). Genetic processes work in combination with an organism's environment and experiences to influence development and behavior , often referred to as nature versus nurture . The intracellular or extracellular environment of

7524-430: The control that does not have that particular disease. DNA samples are obtained from participants and their genome can then be derived through lab machinery and quickly surveyed to compare participants and look for SNPs that can potentially be associated with the disease. This technique allows researchers to pinpoint genes and locations of interest in the human genome that they can then further study to identify that cause of

7638-471: The disease. Karyotyping allows researchers to analyze chromosomes during metaphase of mitosis, when they are in a condensed state. Chromosomes are stained and visualized through a microscope to look for any chromosomal abnormalities. This technique can be used to detect congenital genetic disorder such as down syndrome , identify gender in embryos, and diagnose some cancers that are caused by chromosome mutations such as translocations. Genetic engineering

7752-417: The expression of genes such that proteins are produced only when needed by the cell. Transcription factors are regulatory proteins that bind to DNA, either promoting or inhibiting the transcription of a gene. Within the genome of Escherichia coli bacteria, for example, there exists a series of genes necessary for the synthesis of the amino acid tryptophan . However, when tryptophan is already available to

7866-422: The first recombinant DNA molecule and first recombinant DNA plasmid .   In 1972, Cohen and Boyer created the first recombinant DNA organism by inserting recombinant DNA plasmids into E. coli , now known as bacterial transformation , and paved the way for molecular cloning.   The development of DNA sequencing techniques in the late 1970s, first by Maxam and Gilbert, and then by Frederick Sanger ,

7980-422: The first whole genome was sequenced ( Haemophilus influenzae ), followed by the eventual sequencing of the human genome via the Human Genome Project in 2001. The culmination of all of those discoveries was a new field called genomics that links the molecular structure of a gene to the protein or RNA encoded by that segment of DNA and the functional expression of that protein within an organism. Today, through

8094-416: The gene of interest is already known. Molecular genetics is a scientific approach that utilizes the fundamentals of genetics as a tool to better understand the molecular basis of a disease and biological processes in organisms. Below are some tools readily employed by researchers in the field. Microsatellites or single sequence repeats (SSRS) are short repeating segment of DNA composed to 6 nucleotides at

8208-470: The gene of interest. Mutations may be a missense mutation caused by nucleotide substitution, a nucleotide addition or deletion to induce a frameshift mutation , or a complete addition/deletion of a gene or gene segment. The deletion of a particular gene creates a gene knockout where the gene is not expressed and a loss of function results (e.g. knockout mice ). Missense mutations may cause total loss of function or result in partial loss of function, known as

8322-401: The genome; this technique has wide implications for disease treatment. Molecular genetics has wide implications in medical advancement and understanding the molecular basis of a disease allows the opportunity for more effective diagnostic and therapies. One of the goals of the field is personalized medicine , where an individual's genetics can help determine the cause and tailor the cure for

8436-464: The information an organism uses to function, the environment plays an important role in determining the ultimate phenotypes an organism displays. The phrase " nature and nurture " refers to this complementary relationship. The phenotype of an organism depends on the interaction of genes and the environment. An interesting example is the coat coloration of the Siamese cat . In this case, the body temperature of

8550-406: The inheritance of an allele for yellow or green pea color is unrelated to the inheritance of alleles for white or purple flowers. This phenomenon, known as " Mendel's second law " or the "law of independent assortment," means that the alleles of different genes get shuffled between parents to form offspring with many different combinations. Different genes often interact to influence the same trait. In

8664-427: The largest human chromosome, for example, is about 247 million base pairs in length. The DNA of a chromosome is associated with structural proteins that organize, compact, and control access to the DNA, forming a material called chromatin ; in eukaryotes, chromatin is usually composed of nucleosomes , segments of DNA wound around cores of histone proteins. The full set of hereditary material in an organism (usually

8778-425: The molecular basis of life. He determined it was composed of hydrogen, oxygen, nitrogen and phosphorus. Biochemist Albrecht Kossel identified nuclein as a nucleic acid and provided its name deoxyribonucleic acid (DNA). He continued to build on that by isolating the basic building blocks of DNA and RNA ; made up of the nucleotides : adenine, guanine, thymine, cytosine. and uracil. His work on nucleotides earned him

8892-453: The molecular mechanism behind various life processes. A key goal of molecular genetics is to identify and study genetic mutations. Researchers search for mutations in a gene or induce mutations in a gene to link a gene sequence to a specific phenotype. Therefore molecular genetics is a powerful methodology for linking mutations to genetic conditions that may aid the search for treatments of various genetics diseases. The discovery of DNA as

9006-557: The nature of inheritance in plants. In his paper " Versuche über Pflanzenhybriden " (" Experiments on Plant Hybridization "), presented in 1865 to the Naturforschender Verein (Society for Research in Nature) in Brno , Mendel traced the inheritance patterns of certain traits in pea plants and described them mathematically. Although this pattern of inheritance could only be observed for a few traits, Mendel's work suggested that heredity

9120-500: The offspring of a mating pair. Genes on the same chromosome would theoretically never recombine. However, they do, via the cellular process of chromosomal crossover . During crossover, chromosomes exchange stretches of DNA, effectively shuffling the gene alleles between the chromosomes. This process of chromosomal crossover generally occurs during meiosis , a series of cell divisions that creates haploid cells. Meiotic recombination , particularly in microbial eukaryotes , appears to serve

9234-435: The original sequence. A particularly important source of DNA damages appears to be reactive oxygen species produced by cellular aerobic respiration , and these can lead to mutations. In organisms that use chromosomal crossover to exchange DNA and recombine genes, errors in alignment during meiosis can also cause mutations. Errors in crossover are especially likely when similar sequences cause partner chromosomes to adopt

9348-470: The phenotype of the organism, while the other allele is called recessive as its qualities recede and are not observed. Some alleles do not have complete dominance and instead have incomplete dominance by expressing an intermediate phenotype, or codominance by expressing both alleles at once. When a pair of organisms reproduce sexually , their offspring randomly inherit one of the two alleles from each parent. These observations of discrete inheritance and

9462-543: The process of protein production . It was discovered that the cell uses DNA as a template to create matching messenger RNA , molecules with nucleotides very similar to DNA. The nucleotide sequence of a messenger RNA is used to create an amino acid sequence in protein; this translation between nucleotide sequences and amino acid sequences is known as the genetic code . With the newfound molecular understanding of inheritance came an explosion of research. A notable theory arose from Tomoko Ohta in 1973 with her amendment to

9576-435: The product rule, the sum rule, and more. Geneticists use diagrams and symbols to describe inheritance. A gene is represented by one or a few letters. Often a "+" symbol is used to mark the usual, non-mutant allele for a gene. In fertilization and breeding experiments (and especially when discussing Mendel's laws) the parents are referred to as the "P" generation and the offspring as the "F1" (first filial) generation. When

9690-519: The properties of a protein by destabilizing the structure or changing the surface of the protein in a way that changes its interaction with other proteins and molecules. For example, sickle-cell anemia is a human genetic disease that results from a single base difference within the coding region for the β-globin section of hemoglobin, causing a single amino acid change that changes hemoglobin's physical properties. Sickle-cell versions of hemoglobin stick to themselves, stacking to form fibers that distort

9804-426: The protein itself). Protein structure is dynamic; the protein hemoglobin bends into slightly different forms as it facilitates the capture, transport, and release of oxygen molecules within mammalian blood. A single nucleotide difference within DNA can cause a change in the amino acid sequence of a protein. Because protein structures are the result of their amino acid sequences, some changes can dramatically change

9918-406: The rate of changes in DNA are called mutagenic : mutagenic chemicals promote errors in DNA replication, often by interfering with the structure of base-pairing, while UV radiation induces mutations by causing damage to the DNA structure. Chemical damage to DNA occurs naturally as well and cells use DNA repair mechanisms to repair mismatches and breaks. The repair does not, however, always restore

10032-408: The role of chain terminating codons was elucidated. One noteworthy study was performed by Sydney Brenner and collaborators using "amber" mutants defective in the gene encoding the major head protein of bacteriophage T4. This study demonstrated the co-linearity of the gene with its encoded polypeptide, thus providing strong evidence for the "sequence hypothesis" that the amino acid sequence of a protein

10146-408: The same allele of a given gene are called homozygous at that gene locus , while organisms with two different alleles of a given gene are called heterozygous . The set of alleles for a given organism is called its genotype , while the observable traits of the organism are called its phenotype . When organisms are heterozygous at a gene, often one allele is called dominant as its qualities dominate

10260-401: The second gene epistatic to the first. Many traits are not discrete features (e.g. purple or white flowers) but are instead continuous features (e.g. human height and skin color ). These complex traits are products of many genes. The influence of these genes is mediated, to varying degrees, by the environment an organism has experienced. The degree to which an organism's genes contribute to

10374-506: The segregation of alleles are collectively known as Mendel's first law or the Law of Segregation. However, the probability of getting one gene over the other can change due to dominant, recessive, homozygous, or heterozygous genes. For example, Mendel found that if you cross heterozygous organisms your odds of getting the dominant trait is 3:1. Real geneticist study and calculate probabilities by using theoretical probabilities, empirical probabilities,

10488-509: The separation process they undergo through mitosis. His work along with Theodor Boveri first came up with the Chromosomal Theory of Inheritance, which helped explain some of the patterns Mendel had observed much earlier. For molecular genetics to develop as a discipline, several scientific discoveries were necessary.  The discovery of DNA as a means to transfer the genetic code of life from one cell to another and between generations

10602-653: The shape of red blood cells carrying the protein. These sickle-shaped cells no longer flow smoothly through blood vessels , having a tendency to clog or degrade, causing the medical problems associated with this disease. Some DNA sequences are transcribed into RNA but are not translated into protein products—such RNA molecules are called non-coding RNA . In some cases, these products fold into structures which are involved in critical cell functions (e.g. ribosomal RNA and transfer RNA ). RNA can also have regulatory effects through hybridization interactions with other RNA molecules (such as microRNA ). Although genes contain all

10716-446: The similar molecule RNA instead of DNA as their genetic material. DNA normally exists as a double-stranded molecule, coiled into the shape of a double helix . Each nucleotide in DNA preferentially pairs with its partner nucleotide on the opposite strand: A pairs with T, and C pairs with G. Thus, in its two-stranded form, each strand effectively contains all necessary information, redundant with its partner strand. This structure of DNA

10830-496: The single celled alga Acetabularia . The Hershey–Chase experiment in 1952 confirmed that DNA (rather than protein) is the genetic material of the viruses that infect bacteria, providing further evidence that DNA is the molecule responsible for inheritance. James Watson and Francis Crick determined the structure of DNA in 1953, using the X-ray crystallography work of Rosalind Franklin and Maurice Wilkins that indicated DNA has

10944-429: The standard trial and error approach. Forensic genetics plays an essential role for criminal investigations through that use of various molecular genetic techniques. One common technique is DNA fingerprinting which is done using a combination of molecular genetic techniques like polymerase chain reaction (PCR) and gel electrophoresis . PCR is a technique that allows a target DNA sequence to be amplified, meaning even

11058-441: The strands are separated, new partner strands can be reconstructed for each based on the sequence of the old strand. This property is what gives DNA its semi-conservative nature where one strand of new DNA is from an original parent strand. Although the structure of DNA showed how inheritance works, it was still not known how DNA influences the behavior of cells. In the following years, scientists tried to understand how DNA controls

11172-562: The structures or expression of DNA molecules manifests as variation among organisms. Molecular genetics often applies an "investigative approach" to determine the structure and/or function of genes in an organism's genome using genetic screens .   The field of study is based on the merging of several sub-fields in biology: classical Mendelian inheritance , cellular biology , molecular biology , biochemistry , and biotechnology . It integrates these disciplines to explore things like genetic inheritance, gene regulation and expression, and

11286-478: The stud-book was 247, but a census conducted by the Ministerio de Medio Ambiente y Medio Rural y Marino in 2003 identified only 172. In 2010 a population of 146 was reported, which by 2018 had risen to 320. The Mallorquín may only be black, in all its variations; horses of any other colour can not be registered. Limited white facial markings are permitted, white leg markings are not. The minimum permissible height

11400-564: The study of inheritance in his inaugural address to the Third International Conference on Plant Hybridization in London in 1906. After the rediscovery of Mendel's work, scientists tried to determine which molecules in the cell were responsible for inheritance. In 1900, Nettie Stevens began studying the mealworm. Over the next 11 years, she discovered that females only had the X chromosome and males had both X and Y chromosomes. She

11514-536: The tryptophan synthesis process. Differences in gene expression are especially clear within multicellular organisms , where cells all contain the same genome but have very different structures and behaviors due to the expression of different sets of genes. All the cells in a multicellular organism derive from a single cell, differentiating into variant cell types in response to external and intercellular signals and gradually establishing different patterns of gene expression to create different behaviors. As no single gene

11628-482: The twenty possible amino acids in a protein or an instruction to end the amino acid sequence ; this correspondence is called the genetic code . The flow of information is unidirectional: information is transferred from nucleotide sequences into the amino acid sequence of proteins, but it never transfers from protein back into the sequence of DNA—a phenomenon Francis Crick called the central dogma of molecular biology . The specific sequence of amino acids results in

11742-564: The two Mediterranean breeds and clear separation from the five "Atlantic" Celtic breeds examined, the Asturcón , Gallego , Jaca Navarra , Losino and Pottok . Identification of the breed was begun in 1981 by the Patronato para las Razas Autóctonas de Mallorca. A stud-book was started in 1988, and a breed association , the Associació de criadors i propietaris de cavalls de pura raça Mallorquina ,

11856-545: The two is responsible for inheritance. In 1928 , Frederick Griffith discovered the phenomenon of transformation : dead bacteria could transfer genetic material to "transform" other still-living bacteria. Sixteen years later, in 1944, the Avery–MacLeod–McCarty experiment identified DNA as the molecule responsible for transformation. The role of the nucleus as the repository of genetic information in eukaryotes had been established by Hämmerling in 1943 in his work on

11970-532: The work of the Augustinian friar Gregor Mendel in the mid-19th century. Prior to Mendel, Imre Festetics , a Hungarian noble, who lived in Kőszeg before Mendel, was the first who used the word "genetic" in hereditarian context, and is considered the first geneticist. He described several rules of biological inheritance in his work The genetic laws of nature (Die genetischen Gesetze der Natur, 1819). His second law

12084-403: The zebrafish Danio rerio have been used successfully to study phenotypes resulting from gene mutations. Reverse genetics is the term for molecular genetics techniques used to determine the phenotype resulting from an intentional mutation in a gene of interest. The phenotype is used to deduce the function of the un-mutated version of the gene. Mutations may be random or intentional changes to

12198-518: Was able to conclude that sex is a chromosomal factor and is determined by the male. In 1911, Thomas Hunt Morgan argued that genes are on chromosomes , based on observations of a sex-linked white eye mutation in fruit flies . In 1913, his student Alfred Sturtevant used the phenomenon of genetic linkage to show that genes are arranged linearly on the chromosome. Although genes were known to exist on chromosomes, chromosomes are composed of both protein and DNA, and scientists did not know which of

12312-681: Was an informal network of biologists centered on Max Delbrück that contributed substantially to molecular genetics and the origins of molecular biology during the period from about 1945 to 1970. The phage group took its name from bacteriophages , the bacteria-infecting viruses that the group used as experimental model organisms. Studies by molecular geneticists affiliated with this group contributed to understanding how gene-encoded proteins function in DNA replication , DNA repair and DNA recombination , and on how viruses are assembled from protein and nucleic acid components (molecular morphogenesis). Furthermore,

12426-463: Was essential for identifying the molecule responsible for heredity . Molecular genetics arose initially from studies involving genetic transformation in bacteria . In 1944 Avery, McLeod and McCarthy isolated DNA from a virulent strain of S. pneumoniae , and using just this DNA were able to convert a harmless strain to virulence. They called the uptake, incorporation and expression of DNA by bacteria "transformation". This finding suggested that DNA

12540-579: Was established in 1992. The official breed standard was approved in 2003. The Mallorquín is listed in the Catálogo Oficial de Razas de Ganado de España in the group of autochthonous breeds in danger of extinction. Its status was listed as "critical-maintained" by the Food and Agriculture Organization of the United Nations in 2000 and in 2007. In approximately 2005 the number of Mallorquín horses recorded in

12654-591: Was first observed by Gregor Mendel, who studied the segregation of heritable traits in pea plants, showing for example that flowers on a single plant were either purple or white—but never an intermediate between the two colors. The discrete versions of the same gene controlling the inherited appearance (phenotypes) are called alleles . In the case of the pea, which is a diploid species, each individual plant has two copies of each gene, one copy inherited from each parent. Many species, including humans, have this pattern of inheritance. Diploid organisms with two copies of

12768-421: Was particulate, not acquired, and that the inheritance patterns of many traits could be explained through simple rules and ratios. The importance of Mendel's work did not gain wide understanding until 1900, after his death, when Hugo de Vries and other scientists rediscovered his research. William Bateson , a proponent of Mendel's work, coined the word genetics in 1905. The adjective genetic , derived from

12882-408: Was pivotal to molecular genetic research and enabled scientists to begin conducting genetic screens to relate genotypic sequences to phenotypes. Polymerase chain reaction (PCR) using Taq polymerase, invented by Mullis in 1985, enabled scientists to create millions of copies of a specific DNA sequence that could be used for transformation or manipulated using agarose gel separation. A decade later,

12996-529: Was the inheritance of acquired characteristics : the belief that individuals inherit traits strengthened by their parents. This theory (commonly associated with Jean-Baptiste Lamarck ) is now known to be wrong—the experiences of individuals do not affect the genes they pass to their children. Other theories included Darwin's pangenesis (which had both acquired and inherited aspects) and Francis Galton 's reformulation of pangenesis as both particulate and inherited. Modern genetics started with Mendel's studies of

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