Evolutionary Biology BIOL 3350 Dr Lisa Rapaport Lecture 10 Notes I II III IV V VI VII Forces of Evolution Evolution in small populations A More and more different populations of animals are finding themselves with fewer and fewer individuals that make up the population many animals are becoming extinct Sampling bias A The problem in small populations is sampling bias B After one generation the probability of staying at HWE is the minority less than 20 C Chance deviations because of small population sizes Genetic diversity A Genetic diversity cannot be contained in such a small population Initial founders cannot carry all of the source population s genetics diversity A Lost locus B and alleles from locus A and C because the population was so small 1 Genetic diversity was lost Population bottlenecks A The small amount of genetic diversity due to the small population size will eventually lead to fixation random at which allele becomes fixed Predictions A Look at the effects of genetic drift among a number of small population we can make some predictions about what happens to these groups of populations B All have same starting conditions and then subject to genetic drift C Each population will eventually fix of either allele A1 or allele A2 each goes to either 1 or 0 Small populations A These populations were isolated from each other B These alleles occur at approximate equal frequencies overall C Different isolated populations had greater representations of some alleles over others many of the populations went to fixation for just one of the alleles D Most of the small populations went to fixation or nearly so little genetic diversity within the individual small populations E Diversity has been lost in these small populations F If an allele goes to fixation in a population every individual within that population is homozygous for that one allele G Heterozygosity declines overtime in small populations H Depending on the size of the population is can slowly or quickly lose heterozygosity 1 VIII Tracking demes refer to graph on Slide 13 A A lot of diversity at t 0 B At t 20 the majority of the populations have maintained heterozygosity but some populations are working towards fixation of one of the alleles C At t 80 about half of the populations were fixing towards one allele and the other half of the populations were fixing towards the other allele Fixation A Increasing the population size as fast as possible helps to maintain heterozygosity IX 2
View Full Document
Unlocking...