During a pre-marital clinical genetic screening, a medical counselor analyzes the hemoglob… — JAMB UTME

During a pre-marital clinical genetic screening, a medical counselor analyzes the hemoglobin genotypes of a prospective couple. The man is homozygous normal ( $AA$ ), while the woman is a heterozygous carrier ( $AS$ ) for sickle-cell disease. What percentage of their offspring is expected to inherit a genotype that is completely free of the sickle-cell allele ( $S$ )?

A
$25\%$
$50\%$ Answer
C
$75\%$
D
$0\%$

Answer

50\%

of the offspring are expected to be homozygous normal (

AA

) and completely free of the sickle-cell allele.

In genetic inheritance of hemoglobin traits, a homozygous normal individual (

AA

) produces only normal alleles (

A

). When crossed with a carrier (

AS

) who produces

50\%

normal alleles (

A

) and

50\%

mutant alleles (

S

), half of the resulting offspring inherit an

A

allele from both parents (

AA

). Thus,

50\%

of the offspring are completely free of the sickle-cell allele.

Step-by-Step Solution

Determine the parental genotypes and gametes produced.

Father (

AA

) produces only

A

gametic types (

100\%

). Mother (

AS

) produces

A

and

S

gametes in equal proportions (

50\%

A

50\%

S

According to Mendel's Law of Segregation, alleles segregate during gamete formation.

Perform a genetic cross using a Punnett square.

Combining gametes yields:

50\%

AA

(homozygous normal) and

50\%

AS

(heterozygous carrier).

Random fertilization between father's

A

gametes and mother's

A

S

gametes yields equal probabilities for

AA

and

AS

genotypes.

Identify the proportion of offspring completely free of the sickle-cell allele (

S

The

AA

genotype has zero copies of the

S

allele, which accounts for

50\%

of the total offspring.

Only individuals with genotype

AA

are completely free of the

S

allele;

AS

individuals carry one copy of the allele.

Key Concept

Application of Mendelian genetics in medical counseling for hemoglobinopathy prevention

Estimated Time:1m 30s

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