Question

11. a). The gene that codes for the ABO blood group in humans has three alleles. In a population of 1000 people, the frequency of the I A allele is 0.2, and the frequency of individuals in the population with type O blood is 0.49. What is the frequency of the I B allele in this population? Show your work.
b). In the same population as above, what is the frequency of people with type A blood? Show your work.

Answer 1

a) The answer is 0.1.

The frequency of IA allele is 0.2:
IA = 0.2

The frequency of O individuals is 0.49:
ii = 0.49
Since there is only one possible genotype for O individuals - ii - the frequency of i is square root of the frequency of O individuals:
i = √ii
⇒ i = √0.49
⇒ i = 0.7

Now, we have the frequencies of two alleles (IA and i). To calculate the frequency of IB allele, we will use the formula:
IA + i + IB = 1
⇒ IB = 1 - IA - i
⇒ IB = 1 - 0.2 - 0.7
⇒ IB = 0.1

So, the frequency of IB allele is 0.1.

b) The answer is 0.32. 

There are two possible genotypes for A individuals - $I^{A} I^{A}$ and $I^{A}i$.

Frequency of $I^{A} I^{A}$ is:
$I^{A} I^{A}$ = AI² = 0.2² = 0.04

Frequency of $I^{A}i$ is:
$I^{A}i$ = 2 x AI x i = 2 x 0.2 x 0.7 = 0.28

Frequency of people with type A blood is the sum of these two frequencies:
A = 0.04 + 0.28 = 0.32

The number of people with type A blood would be:
0.32 x 1000 people = 320 people