Question

In a population of Garden-digging Armadillos in HW equilibrium, the C allele for long claws is completely dominant to the c allele for clawlessness. Extensive sampling of this population showed 9% of the armadillos to be clawless.

a. What are the gene and genotypic frequencies of the C locus?

b. On closer examination, wildlife biologists discover that one in four of the clawless armadillos also has webbed feet. A third allele (c^w) for webbed feet causes this condition. It is completely recessive to both the clawed (C) and clawless (c) alleles. What are the gene and genotypic frequencies in the population now?

Answer 1

As dominant allele is C (p)

Recessive is c (q)

Genotype for clawlessness is cc (q²) = 9% or 0.09

So, q = (0.09)^1/2 = 0.3

Hence , p = 1 - 0.3 = 0.7

So, frequency of C = 0.7 or 70%

c = 0.3 or 30 %

CC = 0.7*0.7 = 0.49 or 49%

cc =0.3*0.3 = 0.09 or 9%

Cc = 2*0.7*0.3 = 0.42 i.e. 42%

Answer b)

One in four i.e. 25% of clawless are webbed.

So, frequency of webbed genotype (c_wc_w ) =25% of 9% = 0.25*0.09 = 0.0225 i.e. 2.25% (denoted by r²)

So, frequency of c_w = 0.15 or 15% (denoted by r)

p = 0.7 i.e. 70%

q = 1 - (p+r) = 1 - (0.7+0.15) = 0.15 or 15%

Now, frequency of CC (claw) = 49%

Frequency of cc (clawless) = 2.25%

c_wc_w (webbed) = 2.25%

Cc = Cc_w = (heterozygous clawed)  2*0.7*0.15 = 0.21 or 21% each

cc_w (heterozygous clawless) = 2*0.15*0.15 = 0.45 or 4.5%