Suppose you have a population of flour beetles with 1000 individuals. Normally t

Question

Suppose you have a population of flour beetles with 1000 individuals. Normally the beetles are red, however a mutant black

body color persists in the population. Red is dominant to black, so BB and Bb genotypes are red; bb is black. The population

is in Hardy-Weinberg equilibrium, with frequency of B allele (p) = 0.5 and that of the b allele (q) = 0.5.

What would be the expected frequencies of the red and black phenotypes?

What would be the expected frequencies of the homozygous dominant, heterozygous, and homozygous recessive after 100

generations if the population is under the conditions of Hardy –Weinberg: (Hint: the number of generations here is not

relevant).

What would be the expected red and black allele frequencies if all H-W conditions were met, except that 1,000 black

individuals migrated into the population?

Explanation / Answer

The frequency of homozygous dominant would be p2 = (0.5)2 = 0.25
The frequency of homozygous recessive would be q2 = (0.5)2 = 0.25
The frequency of heterozygotes would be 2pq = 2 x 0.5 x 0.5 = 0.5
Hence the Red phenotype would be 0.75 and black phenotype would be 0.25.
The full figures would be: 0.25 x 1000 = 250 black individuals and 0.75 x 1000 = 750 red individuals.
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After 100 generations if the population still follows Hardy-Weinberg equilibrium, then there will be no change in the frequencies of homozygous dominant, homozygous recessive and heterozygous individuals.
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If 1000 black individuals migrated into the population then the total number of black individuals would be higher.
The number of black individuals in the population now would be 1000 + 250 = 1250.
The number of red individuals would be 750.
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Hence the frequency of the black allele would be 1250/2000 = 0.625

The frequency of the red allele would be 750/2000 = 0.375

Hence all the conditions of Hardy-Weinberg equilibrium are met.

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