Question

A population of water snakes is found on an island in Lake Erie. Some of the snakes are banded and some are unbanded; banding is caused by an autosomal allele that is recessive to an allele for no bands. The frequency of banded snakes on the island is 0.4, whereas the frequency of banded snakes on the mainland is 0.81. One summer, a large number of snakes migrate from the mainland to the island. After this migration, 20% of the island population consists of snakes that came from the mainland.

a. If both the mainland population and the island population are assumed to be in Hardy-Weinberg equilibrium for the alleles that affect banding, what is the frequency of the allele for bands on the island and on the mainland before migration?
b. After migration has taken place, what is the frequency of the banded allele on the island?

Answer 1

A.the frequency of the ringed allele on the island before migration is: 0,9

B. the frequency of the ringed allele on the island after migration is: 0.684

Step-by-step explanation:

A.

when the bands are recessive and there are no dominant bands

Step 1: Calculate the frequency of ringed snakes (q2) on the island before migration.

as a result, q2 = 0.4; q = √q2 = √0.4 = 0.63.

The allelic frequency of ringed snakes on the island before migration is 0.63

we then search on dry land, q2 = 0.81; q = √0.81 = 0.9

B. thus, after migration, the frequency of the ringed allele on the island is:

Step 1

The frequency of the ringed allele on the island after migration = qnew = m * q migrants + (1-m) * qold

we replace with the data:

M = 20% = 20/100 = 0.2

qmigrants = 0.9 (on the island before migration)

qold = 0.63 (on dry land)

so:

qnew = 0.2 X 0.9 + 0.8 X 0.63 = 0.18 + 0.504 = 0.684