This pedigree shows a family where II-1 is affected by an autosomal recessive disorder. Which individuals MUST be heterozygote?

Question

This pedigree shows a family where II-1 is affected by an autosomal recessive disorder. Which individuals MUST be heterozygote?

BlackTom AI · Accepted Answer

Begin by restating the problem context: this pedigree shows autosomal recessive inheritance with II-1 affected. In AR conditions, an affected individual must have two mutant alleles, one from each parent, which implies that the parents are both carriers (heterozygotes).

Option 1: II-2 and II-3. These two individuals are unaffected children of two unaffected parents who produced an affected child (II-1). While it is possible for carriers to be among their genotypes, there is no requirement that II-2 or II-3 must be heterozygotes; they could be non-carriers or carriers, but the pedigree does not force them to be heterozygous. Therefore, this option is not mandatory.

Option 2: Only II-1. II-1 is affected, not a carrier — in autosomal recessive conditions an affected individual has two mutant alleles, not just one. So labeling II-1 as a heterozygote would be incorrect; the individual is homozygous recessive for the disease allele. This option is incorrect.

Option 3: None. If neither parent contributes a disease allele, the condition could not appear in II-1. Since II-1 is affected, at least the parents must carry the allele, making it possible that they are heterozygotes. In fact, both I-1 and I-2 must be heterozygotes. Therefore, claiming none must be heterozygotes is inaccurate.

Option 4: I-1 and I-2. Given that II-1 is affected, each parent must provide one mutant allele, which requires both parents to be carriers (heterozygotes) to produce an affected child in an autosomal recessive pattern. This makes I-1 and I-2 the individuals who MUST be heterozygotes.

Overall, the reasoning shows that only the parental generation carrying the disease allele are obligated to be heterozygotes, while the unaffected siblings may or may not be carriers depending on segregation. The final assessment supports Option 4 as the necessary heterozygotes.

This pedigree shows a family where II-1 is affected by an autosomal recessive disorder. Which individuals MUST be heterozygote?单项选择题

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