In a tropical forest there is a species of bird that has a variable tail length.

Question

In a tropical forest there is a species of bird that has a variable tail length. The Long allele (L) is incompletely dominant over the short allele (l). In one population of 2000 birds, 1280 have long tails (LL), 640 have medium length tails (Ll), and 80 birds have short tails(ll).

a) What is the frequency of each allele in the population?

b) The next year you observe this population of birds and notice the following numbers: 735 long, 630 medium and 135 short. Calculate the genotype and allelic frequencies in this population of birds.

c) What is the absolute fitness of each genotype?

d) What is the relative fitness of each genotype?

e) What allelic frequencies would you expect following another year of poaching? Include your calculation of mean fitness.

f) What are the coefficients of selection in this system?

g) What is the coefficient of dominance in this system?

Explanation / Answer

a)    What is the frequency of each allele in the population?

Genotypic Frequencies

LL=p2=1280/2000=0.64

Ll=2pq=640/2000=0.32

.ll=q2=80/2000=0.04

(p2+2pq+ q2) =0.64+0.32+0.04=1

Alleleic Frequencies

(p2)= p=0.64=0.8

(q2)= q=0.04=0.2

(p2+q2) =0.8+0.2=1

b)    The next year you observe this population of birds and notice the following numbers: 735 long, 630 medium and 135 short. Calculate the genotype and allelic frequencies in this population of birds.

Genotypic Frequencies

LL=p2=735/1500=0.49

Ll=2pq=630/1500=0.42

.ll=q2=135/1500=0.09

(p2+2pq+ q2) =0.49+0.42+0.09=1

Alleleic Frequencies

(p2)=p= 0.49=0.7

(q2)= q=0.09=0.3

(p2+q2) =0.7+0.3=1

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