Слайд 2: GENETIC DRIFT IN HUMAN POPULATION
SUBMITTED BY: DHRUV MANGAL 195 B(LA-2) SUPERVISOR: ANNA ZHUKOVA GENETIC DRIFT IN HUMAN POPULATION
Слайд 3: KEY POINTS
Genetic drift is a mechanism of evolution in which allele frequencies of a population change over generations due to chance (sampling error). Genetic drift occurs in all populations of non-infinite size, but its effects are strongest in small populations. Genetic drift may result in the loss of some alleles (including beneficial ones) and the fixation, or rise to 100\%100%100, percent frequency, of other alleles. Genetic drift can have major effects when a population is sharply reduced in size by a natural disaster ( bottleneck effect ) or when a small group splits off from the main population to found a colony ( founder effect ).
Слайд 4: WHAT IS GENETIC DRIFT?
Genetic drift is change in allele frequencies in a population from generation to generation that occurs due to chance events. To be more exact, genetic drift is change due to "sampling error" in selecting the alleles for the next generation from the gene pool of the current generation. Although genetic drift happens in populations of all sizes, its effects tend to be stronger in small populations. WHAT IS GENETIC DRIFT?
Слайд 6: HISTORY
The role of random chance in evolution was first outlined by Hagedoorn and Hagedoorn in 1921 . They highlighted that random survival plays a key role in the loss of variation from populations. Fisher (1922) responded to this with the first, albeit marginally incorrect, mathematical treatment of the ' Hagedoorn effect'.  Notably, he expected that many natural populations were too large (an N ~10,000) for the effects of drift to be substantial and thought drift would have an insignificant effect on the evolutionary process. The corrected mathematical treatment and term "genetic drift" was later coined by a founder of population genetics, Sewall Wright. His first use of the term "drift" was in 1929,  though at the time he was using it in the sense of a directed process of change, or natural selection. Random drift by means of sampling error came to be known as the "Sewall–Wright effect," though he was never entirely comfortable to see his name given to it. Wright referred to all changes in allele frequency as either "steady drift" (e.g., selection) or "random drift" (e.g., sampling error). [5 HISTORY
Слайд 9: POPULATION SIZE MATTERS
Larger populations are unlikely to change this quickly as a result of genetic drift. For instance, if we followed a population of 100010001000 rabbits (instead of 101010), it's much less likely that the b allele would be lost (and that the B allele would reach 100\%100%100, percent frequency, or fixation ) after such a short period of time. If only half of the 100010001000-rabbit population survived to reproduce, as in the first generation of the example above, the surviving rabbits (500500500 of them) would tend to be a much more accurate representation of the allele frequencies of the original population – simply because the sample would be so much larger. POPULATION SIZE MATTERS
Слайд 19: ALLELE BENEFIT OR HARM DOES NOT MATTER
Allele benefit or harm doesn't matter Genetic drift, unlike natural selection, does not take into account an allele’s benefit (or harm) to the individual that carries it. That is, a beneficial allele may be lost, or a slightly harmful allele may become fixed, purely by chance. A beneficial or harmful allele would be subject to selection as well as drift, but strong drift (for example, in a very small population) might still cause fixation of a harmful allele or loss of a beneficial one.
Слайд 20: SUMMARY
Unlike natural selection, genetic drift does not depend on an allele’s beneficial or harmful effects. Instead, drift changes allele frequencies purely by chance, as random subsets of individuals (and the gametes of those individuals) are sampled to produce the next generation. Every population experiences genetic drift, but small populations feel its effects more strongly. Genetic drift does not take into account an allele’s adaptive value to a population, and it may result in loss of a beneficial allele or fixation (rise to 100\%100% 100, percent frequency) of a harmful allele in a population. The founder effect and the bottleneck effect are cases in which a small population is formed from a larger population. These “sampled” populations often do not represent the genetic diversity of the original population, and their small size means they may experience strong drift for generations. SUMMARY