Genetic drift

evolution- genetic drift

1. -SARASWATI PAWAR BSC. BIOTECHNOLOGY Genetic Drift

2. Genetic Drift The term given by Sewall Wright The random and directionless change in the Allele frequency simply as a result of chance from one generation to next in a small population is called genetic drift. Genetic drift can cause big losses of genetic variation for small populations. Properties of genetic drift : Involves in evolutionary process Random changes It act to eliminate genetic variation class of genetic variation Can lead to homozygous condition Facilitate speciation.

3. Act upon the genetic frequency within a population without regard to their phenotypic effect It can cause harmful allele to become fixed Bottleneck effect and founder effect does not represent the correct frequency of actual population

4. Bottleneck effect Earthquakes, floods, or fires may kill large numbers of individuals, leaving a small surviving population that is unlikely to have the same genetic makeup as the original population. Such a drastic reduction in population size is called a bottleneck effect The bottleneck effect, also known as a population bottleneck, is when a species goes through an event that suddenly and significantly reduced its population

5. Analogous to shaking just a few marbles through a bottleneck at higher frequency in the surviving population than in the original population, others (green marbles) may be present at lower frequency, and some (orange marbles) may not be present at all. After a bottlenecking event, genetic drift may continue for many generations until the population is again large enough for fluctuations due to chance to have less of an impact. Even if a population that has passed through a bottleneck ultimately recovers its size, it may have low levels.

6. Example Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in 1880s Hunting reduced their population size to as few 20 individuals at the end of the 19 th century Their population has since rebounded to over 30000 , but their genes still carry the marks of this bottelneck ; they have much less genetic variation than population of southern elephant seal that was not so intensely hunted.

7. Founder Effect Genetic drift is also likely when a few individuals colonize an island or other new habitat, producing what is called the founder effect. The smaller the group, the less likely the genetic makeup of the colonists will represent the gene pool of the larger population they left . The founder effect explains the relatively high frequency of certain inherited disorders among some human populations established by small numbers of colonists .

8. In 1814, 15 people founded a colony on Tristan da Cunha, a group of small islands in the middle of the Atlantic Ocean. Apparently, one of the colonists carried a recessive allele for retinitis pigmentosa , a progressive form of blindness. Of the 240 descendants who still lived on the islands in the 1960s, four had retinitis pigmentosa , and at least nine others were known to be heterozygous carriers of the allele. The frequency of this allele is 10 times higher on Tristan da Cunha than in the British population from which the founders came. Many genetic diseases are increased in prevalence in human population due in part to the funder effect

9. Bottleneck Effect Founder Effect Subpopulation caused when a natural disaster reduces the size of an original population. Results of habitat fragmentation or over exploitation of species. Establishes a subpopulation as a new colony drawn from a larger population. Result of migration.