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# Population Genetics?

Heterozygosity is 0.40 at a polymorphic gene in a population of 20 trees. If the population maintains the same size over generations, what is the expected level of heterozygosity two generations later?

### 1 Answer

- JazSincLv 73 years agoFavorite Answer
o I have no expectations.

o Is evolution occurring? If it is, that's going to skew the results.

o Trees don't have discrete generations, so "two generations later" is meaningless.

o We're not told how many different alleles there are at this gene locus.

o That out of the way, and assuming there are only two alleles, I still can't perform the calculation because I don't know enough about the homozygotes in the initial population.

Homozygotes comprise 0.6 of the population (since we're told that heterozygotes are 0.4).

What if that 0.6 is all one form:

The population is entirely AA and Aa with NO aa. You have 40 alleles divided as 12 homozygote trees and 8 heterozygote trees. Assuming no evolution,

24 + 8 = 32 A alleles; freq(A) = 32/40 = 0.8

8 a alleles = 0.2

Future generations will have those proportions, heterozygosity would be

2pq = 2 * 0.8 * 0.2 = 0.32

What if that 0.6 is divided evenly:

The population is 0.3 AA (6 trees) and 0.4 Aa (8 trees) and 0.3 aa (6 trees). Assuming no evolution, you have

6 + 6 + 8 = 20 A alleles freq(A) = 20/40 = 0.5

8 + 6 + 6 = 20 a alleles freq(a) = 20/40 = 0.5

Future generations will have those proportions, heterozygosity would be

2pq = 2 * 0.5 * 0.5 = 0.5

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Yeah. Your teacher should rephrase the question, including all the necessary assumptions.

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