Question 1
The frequency of the 'D' allele is 0.34 in a population of 1378 people. Assuming that it is an ideal population,
a. How many homozygous recessive people are in the population?
As discussed previously, we take the dominant allele frequency as p and recessive as q. So;
p=0.34, and since p+q=1, q=1-p=1-0.34=0.66
If they ask for homozygous recessive people, they are basically asking for genotypic frequency(a genotype makes up a person, not an allele). So they are asking for the frequency of 'dd' which is q2
q2=0.662=0.4356. Therefore, the number of homozygous recessive people is 0.4356×1378=600 people
b. How many heterozygous people are in the population?
In this case, they are asking for the genotypic frequency of 'Dd' which is 2pq=2×0.34×0.66=0.4488
Therefore, the number of heterozygous people is 0.4488×1378=618 people
Just a reminder that the allelic and genotypic frequencies must never be greater than one. They are relative frequencies and probabilities and as you remember from the Biostatistics course, probability can never be greater than one.
Question 2
In a Hardy-Weinberg population, 800 people express the dominant phenotype for a certain trait while the remaining 300 expresses the recessive phenotype.