Genetic variability


Genetic variability

Genetic variability is a measure of the tendency of individual genotypes in a population to vary from one another. Variability is different from genetic diversity, which is the amount of variation seen in a particular population. cite book| title=Variation and Variability| year=1995| publisher=Yale University| accessdate=2007-05-24| url=http://www.cbc.yale.edu/old/cce/papers/ALife/node2.html ] The variability of a trait describes how much that trait tends to vary in response to environmental and genetic influences. Genetic variability in a population is important for biodiversity, because without variability, it becomes difficult for a population to adapt to environmental changes and therefore makes it more prone to extinction. Variability is an important factor in evolution as it affects an individual's response to environmental stress and thus can lead to differential survival of organisms within a population due to natural selection of the most fit variants. Genetic variability also underlies the differential susceptibility of organisms to diseases and sensitivity to toxins or drugs — a fact that has driven increased interest in personalized medicine given the rise of the human genome project and efforts to map the extent of human genetic variation such as the HapMap project.

Causes of Variability

There are many sources of genetic variability in a population:

*Genetic recombination is one source of variability; during meiosis in sexual creatures two homologous chromosomes from the male and the female cross over one another and exchange gene sequences. The chromosomes then split apart and are ready to form an offspring. The cross-over is random and is governed by its own set of genes that code for where crossovers can occur (in cis) and for the mechanism behind the exchange of DNA chunks (in trans). Being controlled by genes means that recombination is also variable in frequency, location, thus it can be selected to increase fitness by nature, because the more recombination the more variability and the more variability the easier it is for the population to handle changes. [ cite journal| author=Burt, Austin| title=Perspective: Sex, Recombination, and the Efficacy of Selection—Was Weismann Right?| journal=Evolution: International Journal of Organic Evolution| issue=54.2 |year=2000| pages=337–351 ]

*Immigration, emigration, and translocation – each of these is the movement of an individual into or out of a population. When an individual comes from a previously genetically isolated population into a new one it will increase the genetic variability of the next generation if it reproduces. cite journal| author=Ehrich, Dorothy and Per Erik Jorde| title=High Genetic Variability Despite High-Amplitude Population Cycles in Lemmings| journal=Journal of Mammalogy| issue=86.2| year=2005| pages=380–385| doi=10.1644/BER-126.1| volume=86 ]

*Polyploidy – having more than two homologous chromosomes allows for even more recombination during meiosis allowing for even more genetic variability in one's offspring.

*Diffuse centromeres – in asexual organisms where the offspring is an exact genetic copy of the parent, there are limited sources of genetic variability. One thing that increased variability, however, is having diffused instead of localized centromeres. Being diffused allows the chromatids to split apart in many different ways allowing for chromosome fragmentation and polyploidy creating more variability. cite journal| author=Linhart, Yan and Janet Gehring| title=Genetic Variability and its Ecological Implications in the Clonal Plant Carex scopulurum Holm. In Colorado Tundra| journal=Arctic, Antarctic and Alpine Research| issue=35.4 |year=2003| pages=429–433| doi=10.1657/1523-0430(2003)035 [0429:GVAIEI] 2.0.CO;2| volume=35 ]

*Genetic mutations – contribute to the genetic variability within a population and can have positive, negative, or neutral effects on an fitness. cite book| author=Wills, Christopher| title=Genetic Variability| publisher=NewYork: Oxford University Press| year=1980 ] This variability can be easily propagated throughout a population by natural selection if the mutation increases the affected individual's fitness and its effects will be minimized/hidden if the mutation is deleterious. However, the smaller a population and its genetic variability are, the more likely the recessive/hidden deleterious mutations will show up causing genetic drift.

References


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • genetic variability — genetinis kintamumas statusas T sritis augalininkystė apibrėžtis Kintamumas, apimantis augalų su naujais paveldimais požymiais ir savybėmis susidarymą mutacijų ir rekombinacijos būdais. atitikmenys: angl. genetic variability rus. генетическая… …   Žemės ūkio augalų selekcijos ir sėklininkystės terminų žodynas

  • genetic variability — Inheritable variation caused by genetic change not by environment …   Dictionary of invertebrate zoology

  • free genetic variability — free genetic variability. См. свободная генетическая изменчивость. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Genetic diversity — is a level of biodiversity that refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary.The academic… …   Wikipedia

  • Variability — The term , the state or characteristic of being variable , may be applied to many different subjects:*Solar van *Human variability *Genetic variability *Heart rate variability *Spatial variability *Statistical variability *Climate variability …   Wikipedia

  • genetic selection — The process of selecting genes, cells, clones, etc., within populations or between populations or species. Genetic selection usually results in differential survival rates of the various genotypes, reflecting many variables, including the… …   Glossary of Biotechnology

  • Genetic determinism — is the belief that genes determine physical and behavioral phenotypes. The term may be applied to the mapping of a single gene to a single phenotype or to the belief that most or all phenotypes are determined mostly or exclusively by genes. While …   Wikipedia

  • Genetic origins of the Turkish people — The migrations of Turkic speaking groups in Anatolia was a shift in language barrier between Altaic languages and Indo European languages. The nature of this exchange has been subject of long debates by the scientists. Anatolia and the medieval… …   Wikipedia

  • variability — noun ADJECTIVE ▪ considerable, extreme, great, high, wide ▪ There is considerable variability in all the test scores. ▪ low ▪ …   Collocations dictionary

  • Genetic origins of Down syndrome — Down syndrome is a chromosomal abnormality characterized by the presence of an extra copy of genetic material on the 21st chromosome, either in whole (trisomy 21) or part (such as due to translocations). The effects of the extra copy varies… …   Wikipedia