Question

select the correct answer. tay - sachs disease is caused by a mutation in the hexa gene located on chromosome 15. tay - sachs follows an autosomal recessive pattern of inheritance. with the help of the diagram, identify which of the offspring will be an unaffected carrier.

Explanation:

Step1: Define genotype rules

Autosomal recessive:

• Affected: $rr$
• Carrier (unaffected): $Rr$
• Unaffected non-carrier: $RR$

Step2: Analyze parent (A) genotype

Individual A is affected, so genotype: $rr$

Step3: Analyze offspring genotypes

Parent A can only pass $r$. The other parent passes either $R$ or $r$:

• Offspring B: $Rr$ (1 $R$, 1 $r$)
• Offspring C: $Rr$ (1 $R$, 1 $r$)
• Offspring D: $RR$ (2 $R$)

Step4: Identify unaffected carriers

Unaffected carriers have $Rr$ genotype: B and C.

Answer:

B and C (the offspring labeled B and C, with genotype $Rr$, are unaffected carriers)