Chapter A, Problem 1P

Match each statement (a-e) with the best answer from the following list: consultand, $\text{50\%}$, prior probability, $66.7\%$, obligate carrier, $100\%$.

a. The Mendelian risk that a person is a heterozygous carrier of a recessive condition.

b. A person who on the basis of family history must be a heterozygous carrier of a recessive mutant allele.

c. The probability that the healthy brother of a women with an autosomal recessive condition is a heterozygous carrier.

d. The person receiving genetic counseling.

e. The probability that the son of a woman with an autosomal recessive condition is a heterozygous carrier.

Summary Introduction

To analyze:

Match the following statements with the best answer –

a. The Mendelian risk that a person is a heterozygous carrier of a recessive condition.	Consultand
b. A person who on the basis of family history must be a heterozygous carrier of a recessive mutant allele	$50\%$
c. The probability that the healthy brother of a woman with an autosomal recessive condition is a heterozygous carrier	Prior probability
d. The person receiving genetic counseling	$66.7\%$
e. The probability that the son of a woman with an autosomal recessive condition is a heterozygous carrier	Obligate carrier
	$100\%$

Introduction:

The identification and classification of various types of hereditary diseases and the genetic counseling plays an important role in medical genetics.

Explanation of Solution

1. The Mendelian risk that a person is a heterozygous carrier of a recessive condition - Prior probability. It is often the Mendelian probability and the likelihood that the hypothesis that an individual has a certain genotype is true.

2. A person, on the basis of family history, must be a heterozygous carrier of a recessive mutant allele - Obligate carrier. A person with a heterozygous genotype will show one autosomal allele and one recessive allele. In case of recessive conditions, recessive phenotype is expressed only when two recessive alleles are present i.e, homozygous recessive condition. A person with heterozygous genotype will express dominant phenotype, and therefore, will be an obligate carrier for a recessive disorder.

3. The probability that the healthy brother of a woman with an autosomal recessive condition is a heterozygous carrier – $50\%$.

   Consider A as a dominant autosomal allele and “a” as a recessive autosomal allele

   A woman has an autosomal recessive condition i.e., genotype of woman will be aa

   Brother is healthy and heterozygous carrier i.e., genotype of brother will be Aa.

   Therefore, parental genotypes will be Aa and aa.

   ♂ ♀	A	a
   A	Aa	aa
   A	Aa	aa

4. The person receiving genetic counseling – Consultand. Consultands are individuals whose concerns, personal, familial and social issues related to the genetic condition in question are consulted by a genetic counselor.

5. The probability that the son of a woman with an autosomal recessive condition is a heterozygous carrier – $100\%$.

   Consider A as a dominant autosomal allele and “a” as a recessive autosomal allele

   A woman with an autosomal recessive condition will have a genotype aa.

   For a son to be heterozygous carrier, father has genotype AA.

   Consider AA to be a genotype of father –

   ♂ ♀	A	A
   a	Aa	Aa
   a	Aa	Aa

Conclusion

The given statements are matched with the best suited answer.