Question

In a particular species of salamander, the skin can either be black or brown. The black phenotype is recessive to the brown phenotype. Within a population of 1000 salamanders, 640 have the brown phenotype. Calculate the allele frequencies for this population. Show all of your work. How many heterozygotes are there? Make up an environmental change that could occur (not an oil spill or something we’ve talked about, invent your own) that would cause a shift in the allele frequencies. How would your environmental change affect p and q?

Answer 1

In a population of 1000 salamanders,
Brown phenotype = 640 (p)
Black phenotype = 1000 -640 = 360 (q)

Allele frequencies of the phenotypes :

p = brown = (2 x 640) / 2000 = 0.64
q = black = (2 x 360) / 2000 = 0.36

Heterozygotes can be calculated by : p2 + 2pq + q2 =1

(0.64)2 + 2pq + (0.36)2 = 1
or, 0.4096 + 2pq + 0.1296 = 1
or, 2pq = 1 - 0.5392 = 0.4608
Heterozygote population = 0.46

An environmental change that can cause change in the allele frequency can be formation of a stream between the rocks that had the population of salamanders due to extreme flood that would lead to migration. Salamanders generally live under rocks or creeks near moist areas. For suppose, if there is a migration of 100 black and 40 brown salamanders from their original population to a new rock that is on the other side of the stream, there will be genetic drift that would cause the population of the original habitat to have a change in the allele frequency. With 100 black and 40 brown gone, the allele frequencies now will be different in the entire 1000 population:

p = 640-100 = 540 = (2 x 540) / 2000 = 0.54
q = 360-40 = 320 = (2 x 320) / 2000 = 0.32

Therefore, there will be no Hardy-Weinberg equlibrium established due to inequal migration.