LECTURE 19 (Drift and migration PG 4) Flashcards
what does sampling lead to?
drift
what are the three ways by which sampling can occur?
- founder effect and bottle necks
- different family sizes
- not all gametes will contribute to the gene pool
what is sampling, explain with an example.
you have a pop with e.g 60 individuals and the allele frequency of A and a are both 0.5 if you randomly take imdv from that pop they’re gonna be either A or a and this is gonna be random, maybe the first time you do sampling results in allele freq of A= 0.2 and a= 0.8 but the second time might be completely different this explains why genetic drift is random bc sampling is random
what’s the fisher -wright model?
it’s a model to explain how drift affects pop, first of all in order for drift to occur the characteristics have to be the same as in HWE bu a finite population size. once this occurs, you can see that in different replicates different alleles will become fixed or lost thus genetic drift is random. , populations act independently.
What are the assumptions of fisher - wright model?
- pop are of finite size
the rest are the assumptions of HWE
What are the key points of genetic drift.
- genetic drift acts faster in smaller populations
- drift is gonna lead to the fixation or lost of alleles through generations
- the time to fixation of an allele in a population is 4N
- drift decreases variation within populations but increase differentiation btw populations
- the probability of an allele becoming fixed at t time is the frequency of that allele at that time
- 1/2N is the frequency of a new mutation in the gene pool (or prob of new mutation arising), thus fixation of mutation when arises is 1/2N and 1- 1/2N = mutation being lost
- ## genetic drift is causing neutral genes to change in frequency
explain with an example why genetic drift acts faster in smaller populations.
if a pop is of 1 individual (can self..) who is Aa th next generation the p of being homo for A is 0.25 homo for a is 0.25 and to remain hetero Aa is 0.5 however if there’s a pop with two imdv this numbers vary and in the second generation the probability of becoming homo for either is 0.06 thus the smaller the population the faster an allele can become fixed.
what’s neutral evolution?
when the frequency of a neutral gene changes due to drift
what’s migration? does it have to do with drift?
migration is equal to gene flow and it’s a counter to drift because drift makes alleles to become fixed or lost whereas migration brings the alleles back
what’s drift?
it’s an stochastic process that fixes or losses alleles in a pop completely random
What’s a bottleneck?
reduction in pop due to a catastrophic event and this reduction leaves a pop that is not representative
what’s founder effect?
some migrants come from a pop and they’re not representative of that pop
what’s Fst
is a measure of genetic differentiation and deficit in homozygotes due to drift
examples of migration in nature.
humans begin with timetants but small fat there was migration no physical barrier
water spiders of different rivers a lot of differentiation bc there was no migration bc there was a physical barrier
why is migration a key thing?
because it stops differentiation btw generations
