Question

Baldness is governed by a sex-influenced trait which is dominant in men and recessive in women. In a sample of 10,000 men, 7225 were found to be non-bald. In a sample of equivalent size how many non-bald women are expected?

Answer 1

• In this case, the baldness is a sex-influenced trait, which means that its expression is influenced by the sex of the individual.
• This baldness is dominant in men and recessive in women.
• Now, let's denote the dominant allele for baldness as B and the recessive allele as b.
• As baldness is dominant in men, the non-bald men would have the genotype of Bb or BB, as they can be the carriers of the recessive allele but still express the dominant trait.
• The women would need to be homozygous recessive (bb) as they express the non-bald phenotype.
• In the sample, it is given that out of 10,000 men, 7,225 are non-bald expressing the dominant phenotype Bb or BB.
• From this information, now let's calculate the frequency of the recessive allele (b) in men:
• Frequency of non-bald men (BB or Bb) = 7,225 / 10,000

                                                                        = 0.7225

• As baldness is recessive in women, we can use the Hardy-Weinberg equation to calculate the frequency of the recessive allele (b) in women.
• In a population, the allele frequencies are represented by p and q.
• So, p^2 + 2pq + q^2 = 1.
• Here- p = frequency of the dominant allele (B)
• q = frequency of the recessive allele (b)
• We have calculated that q = 0.7225, so we can solve for p as follows -
• p = 1 - q p = 1 - 0.7225 p = 0.2775
• So, now, let's find the frequency of non-bald women (bb) as follows -
• Frequency of non-bald women (bb) = q^2

                                                                   = (0.7225)^2

                                                                   ≈ 0.5223

• Now finally, we can determine the number of non-bald women in a sample of 10,000 women which is equivalent to the men's sample size -
• Number of non-bald women = Frequency of non-bald women × Total sample size Number of non-bald women
• = 0.5223 × 10,000
• ≈ 5,223
• Therefore, in a sample of equivalent size of 10,000 women, approximately 5,223 women are expected to be non-bald.

Sex-influenced trait:

• It is also known as a sex-influenced inheritance pattern which refers to a genetic trait whose expression is influenced by the sex of the individual.
• It is also referred to as the presence or absence of the trait is determined by the individual's sex and the interaction between their sex chromosomes and other genetic factors.
• In this case, the same allele may lead to different phenotypic expressions in males and females due to hormonal or other physiological differences between the sexes.
• These traits are often associated with genes located on autosomal chromosomes rather than the sex chromosomes.