6. Consider the following population of really cool stream-dwelling salamanders:

Question

6. Consider the following population of really cool stream-dwelling salamanders: A1A1 A1A2 A2A2 Relative frequencies 0.60 0.30 0.10 Probability of survival 0.60 0.80 0.40 Number of offspring 15.0 5.0 10.0

a. Calculate the relative fitness of each genotype.

b. Calculate the selection coefficient for each genotype.

c. If the strength and direction of natural selection in this population remain the same, what will the frequency of the A1 and A2 alleles be when the population reaches Hardy-Weinberg equilibrium (just explain in words, you do not need math)?

d. Calculate p for A1 assuming that the strength and direction of natural selection remain unchanged.

e. Now suppose that the probability of survival for the A2A2 genotype increased to 0.90, but everything else remained the same. How would this change your answer to part c)?

Explanation / Answer

Question a.

Survival rate :

A1A1 = 60% ; A1A2 = 80% ; A2A2 = 40%

Relative fitness (w) :

A1A1 = 60/80 = 0.75

A1A2 = 80/80 = 1

A2A2 = 40/80 = 0.5

Question b)

selection coefficient ( 1-w ) :

A1A1 (w= 0.75)

s = 1 - 0.75 = 0.25

A1A2 (w= 1)

s = 1 - 1 = 0.00

A2A2 (w= 0.5)

s = 1 - 0.5 = 0.5

Question C)

When the population reaches Hardy Weinberg equilibrium A1 will be denoted by p and A2 will be denoted by q and they will be given as :

p2 + q2 + 2pq = 1

Question D)

The frequency of p = [ ( 2 x 15 ) + 5 ] / 60

p = 0.58

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