Question

1) A population of endangered freshwater threespine sticklebacks (Gasterosteus aculeatus) live in a pond on Salt Spring Island off the BC coast. 396 individual are red-throated and 557 are black-throated. Assume that throat colour is controlled by a single locus with two alleles (A and a) and that red throats are completely recessive. Calculate the following:

a) The frequency of each allele.

b) The genotype frequencies assuming Hardy-Weinberg.

c) The number of heterozygous individuals that you would expect in this population.

d) Conditions happen to be really good for breeding in the following year and the population increases to 1412 sticklebacks. If all of the Hardy-Weinberg conditions are met, how many of these would you expect to be red-throated and how many black-throated?

Answer 1

Question 1

Here it is given that

Red throated = 396

Blackthroted = 557

so here if p is the frequency of Allele A and q is the frequency of Allele a.

so here

AA = 396

2Aa + aa = 557

p²n = 396

(2pq + q²)n = 557

(2pq + q²)/p² = 557/396

792pq + 396q² = 557p²

557(p/q)² - 792 (p/q) - 396 = 0

now solving quadratic equation we get

p/q = 1.8138

p = 1.8138 * (1 - p)

p = 1.8138 - 1.8138p

p = 0.6446

q = 0.3554

(b)

Now genotype frequency assuming Hardy - weing berg

AA = 396

Aa = 437

aa = 120

(c Here number of heterozygous individuals that you would expect in this population. = 437

(d) Now population = 1412 sticklebacks

so here

red throated = 1412 * 0.6446² = 587

black throated = 825