Question

$9\%$ of Hardy- Weinberg population of 800 are recessive. How many of this population are heterozygous?
A. $336$
B. $392$
C. $372$
D. $362$

Answer 1

Hardy- Weinberg law states that in the absence of any evolutionary impacts from one generation to the next, the genotype and allele frequencies in a vast, random-mating population stay constant. Natural selection, genetic drift, mutation, sexual selection, gene flow, genetic hitchhiking, founder effect, meiotic drive, population bottleneck, inbreeding, and assortative mating are examples of influences.
Applications of the Hardy-Weinberg Principle are- Complete Dominance, multiple alleles, linkage disequilibrium, Frequencies If Harmful Recessive Alleles.

Complete answer:
Option A: According to the Hardy-Weinberg principle,
${p^2}{\text{ }} + {\text{ }}2pq{\text{ }} + {\text{ }}{q^2}{\text{ }} = {\text{ }}1$
where p and q represent the individual allele frequencies.
So, ${p^2} =$ frequency of homozygous conditions represented by p.
${q^2} =$ frequency of homozygous alleles represented by q.
$2pq{\text{ }} =$ frequency of heterozygous condition.
Here, ${p^2}{\text{ }} = {\text{ }}0.09$, hence $p{\text{ }} = {\text{ }}0.3$
Using $p{\text{ }} + {\text{ }}q{\text{ }} = {\text{ }}1$, $q{\text{ }} = {\text{ }}0.7$
So, the allelic frequency of heterozygous population,
$2pq{\text{ }} = {\text{ }}2{\text{ }} \times {\text{ }}0.3{\text{ }} \times {\text{ }}0.7{\text{ }} = {\text{ }}0.42$
So, the heterozygous population $= {\text{ }}0.42{\text{ }} \times {\text{ }}800{\text{ }} = {\text{ }}336$.
So, the correct option is $336$.
Hence option A is correct.
Option B: It means that $42\%$ of the population is heterozygous. So, out of 800 people, there will be $\dfrac{{800 \times 42}}{{100}} = 336$ heterozygous genotypes.
So, option B is not correct.
Option C: heterozygous population for the above question is $336$.
So, option C is incorrect.
Option D: t indicates that $42\%$ of the population is heterozygous for one of the two chromosomes. So, there will be $\dfrac{{800 \times 42}}{{100}} = 336$ heterozygous genotypes out of 800 persons.
So, option D is incorrect.

Hence, Option A is the correct answer.

Note:
Factors affecting the Hardy-Weinberg principle are Mutation, Genetic drift, Natural selection, Genetic recombination, Gene flow. All of these factors play a role in a species' gene frequency changing throughout time. The gene frequency changes again when a few individuals from a species migrate to a new location. It decreases where people migrate from and increases where they go to. The founder effect occurs when the frequency of genes in a newly migrated land is high enough to create a new species, and the migrated individuals become the founder species. As a result, all of these mechanisms contribute to the evolution process.