Question

you sampled 550 college students and found that 352 have Darwins tubercle. a) what are the frequencies of alleles T and t? b) what are the genotype frequencies (TT, Tt and tt) ? c) if the expected allele frequencies are equal, what are the expected genotype frequencies? d) what does this tell you about the population?

Answer 1

According to Hardy Weinberg equilibrium

p+q=1 where p is the frequency of dominant allele (here T) and q is the frequency of recessive allele (here t)

p2 + 2pq +  q2 = 1,

where p2 is the frequency of homozygous dominant genotype (here TT)

2pq is the frequency of heterozygous genotype (here Tt)

q2 is the frequency of homosygous recessive genotype (tt)

a) Darwin's Tubercle is considered a dominant trait. which means TT and Tt will have tubercle while tt will not have it.

This means that out of 550 students 198 studens (550-352) do not have tubercle.

so the percentage of tt people in the population is the genotype frequency of tt or q2 = 198/550 = 0.36 ( means 36% of the students have no tubercle)

Allele frequency of q = 0.6 (square root of 0.36)

p= 1-0.6 = 0.4

b) therefore

genotype frequency of TT = p2 = 0.16

genotype frequency of Tt = 2pq = 0.48

genotype frequency of tt =q2= 0.36

c) Since the sum of the allele frequencies is equal to 1, if the expected allele frequencies are equal that means p=q= 0.5 (since 0.5 +0.5 =1)

This means expected genotype frequencies are TT = 0.5 X 0.5 = 0.25

Tt = 2X0.5 0.5 = 0.5

tt = 0.5 x 0.5 = 0.25