BIOL 2040 Lecture Notes - Lecture 6: Genotype Frequency, Allele Frequency, Peppered Moth
27 Apr 2018
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Lecture 6 - Drift (end)
January 25, 2018
9:49 PM
Example: Which population has more variation?
Freq AA
Freq Aa
Freq aa
Population 1:
P = 0.4
0.28
0.24
0.48
Population 2:
P = 0.7
0.49
0.42
0.09
How do you measure variation? You calculate 2pq to find He, which is the expected heterozygosity.
Population 2:
He = 2pq
He = 2(0.7)(0.3) = 0.42
This population is in HWE (Hardy Weinberg Equilibrium) because if you calculate p2, 2pq, and q2,
the numbers match the current genotype frequencies.
Population 1:
He = 2pq
He = 2(0.4)(0.6) = 0.48
This population is not in HWE because if you calculate p2, 2pq, and q2, the numbers do not match
the current genotype frequencies.
Because population one has a higher He, it has more variation. The closer the He is to 0.5 (from 0-0.5),
the closer the present alleles are 50/50.
Population Divergence is a kind of Inbreeding
• Looking at the whole population, the He averages at around 0.5
• When each of the subpopulations are looked at, the average He is 0.2, and many have a p of 1.0
with an He of 0, while other populations have a p of 0 and an He of 0
Consider migration: In evolution, migration refers to movement between populations (as opposed to
founding of new populations). We have considered the divergence of separate, isolated populations due
to drift. What if the populations aren't completely isolated?
Migration
• m = migration rate
• Ex. If a population has a migration rate of 0.2, it is the proportion of the population that
immigrates from the continent to the island each generation.
o On the continent: p = 0.0
• Assume this stays constant.
o On island: p = 0.1, at the beginning. It will change with migration.
o This is if there is no selection, mutation, or drift
• Theory:
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