A mainland population of 1000 blue iguanas have the neutral alleles A1 and A2 wi

Question

A mainland population of 1000 blue iguanas have the neutral alleles A1 and A2 with frequencies of A1 = 0.50 and A2 = 0.50.

A new population of blue iguanas is founded on Lizard Island with a population size of 10 males and 15 females.The neutral alleles A1 and A2 are present in the population with frequencies of A1 = 0.30 and A2 = 0.70. Migrants begin moving from the mainland to Lizard Island at a rate of 1 migrant per generation.

1. Calculate the change in frequency (?p) of the A1 allele after one generation of migration.

2. What will the new frequency (p?) of A1 be in the island population after one generation of migration ?

Explanation / Answer

Given data:

Frequency of mainland population A1m = 0.50 and A2m = 0.50; population size Nm = 1000

Frequency of mainland population A1i = 0.30 and A2i = 0.70; population size Ni = (10+15=)25

Genotype frequency of A1A1 in island = 0.30*0.30 = 0.09; Genotype frequency of A2A2 in island = 0.70*0.70 = 0.49; Genotype frequency of A1A2 in island = 2*0.30*0.70 = 0.42. Note that out of 25, 9% will have A1A1 genotype (9% of 25 = 2.25~2) and 42% will have A1A2 genotype (42% of 25 =10.5~11); A2A2 = (49% of 25) =12.25~12. Allele frequency of A1 (i.e. ‘p’) = {0.09 + (½ *42)} = 0.3.

Now, one migrant moves from mainland to island in one generation.

So, new population size of the island = (25 + 1 =) 26

***Note that your answer will depend on the genotype that has migrated; the genotypes can be A1A1, A1A2 and A2A2.

Let us consider that the migrant that had moved had the genotype A1A1.

So, A1A1 = 3.25; A1A2 (=10.5) and A2A2 (=12.25) will remain the same.

Calculate percentages:

New genotype frequency of A1A1 = 100*3.25/26 = 12.5%;

New genotype frequency of A1A2 = 100*10.5/26 = 40.38%;

New genotype frequency of A2A2 = 100*12.25/26 = 47.11%;

So, new frequency of A1 = p (new) after one generation = {0.125 + (½ *0.4038)} ~ 0.33 (Answer 2)

Change in genotype frequency = (0.33 – 0.3) =0.03 (Answer 1)

Note: Your answer will vary when you change the genotype that has been transferred (mentioned before also).

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