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Difficulty: MediumApplications of Genetics in Medicine and Agriculture

A genetic counselor evaluates a married couple who are both heterozygous carriers of the sickle-cell gene (HbAHbSHb^A Hb^S). What is the probability that their first child will be an asymptomatic carrier of the sickle-cell trait?

  1. A
    25%
  2. 50%Answer
  3. C
    75%
  4. D
    100%

Answer

The probability that the couple's first child will be an asymptomatic carrier of the sickle-cell trait is 50%.
When two heterozygous individuals (HbAHbSHb^A Hb^S) produce offspring, Mendelian segregation yields a genotypic ratio of 1 HbAHbAHb^A Hb^A (normal, 25%) : 2 HbAHbSHb^A Hb^S (carrier trait, 50%) : 1 HbSHbSHb^S Hb^S (sickle-cell anemia, 25%). Therefore, there is a 50% chance that any child born to them will be an asymptomatic carrier.

Step-by-Step Solution

1
Determine parental genotypes
Both parents are heterozygous carriers with the genotype HbAHbSHb^A Hb^S.
Sickle-cell trait is an autosomal codominant condition where carriers possess one normal hemoglobin allele (HbAHb^A) and one sickle hemoglobin allele (HbSHb^S).
2
Perform a monohybrid cross between the parents (HbAHbS×HbAHbSHb^A Hb^S \times Hb^A Hb^S)
The possible offspring genotypes are 1 HbAHbAHb^A Hb^A : 2 HbAHbSHb^A Hb^S : 1 HbSHbSHb^S Hb^S.
Gametes from each parent separate independently during meiosis, giving equal likelihood for inheriting either allele.
3
Calculate the proportion corresponding to asymptomatic carriers (HbAHbSHb^A Hb^S)
Heterozygous carrier probability = 24=50%\frac{2}{4} = 50\%.
Two out of the four possible genotypic outcomes result in the carrier state (HbAHbSHb^A Hb^S).

Key Concept

Application of genetic inheritance in medical counseling for sickle-cell trait
Estimated Time:1m 0s
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Topics

Applications of Genetics in Medicine and Agriculture

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