Question at position 17 The genotype of individual II-2 is Homozygous dominantHomozygous recessiveheterozygoushemizygousCannot be determined from the pedigree

Question

BlackTom AI · Accepted Answer

Let's examine the pedigree step by step and assess what each option would imply.
Option: Homozygous dominant. If II-2 were AA (homozygous dominant) and the trait is autosomal recessive (as suggested by affected individuals in the family), we would expect II-2 to be unaffected unless the trait is dominant. However, the presence of affected individuals in the pedigree (e.g., II-4 is shaded) indicates the trait is recessive, not dominant. Therefore II-2 cannot be confidently labeled as AA.
Option: Homozygous recessive. If II-2 were aa (homozygous recessive), she would be affected. But II-2 is depicted as an unaffected circle, not shaded. This makes aa incompatible with her phenotype, so this option is not viable.
Option: Heterozygous. Given the trait appears autosomal recessive (since there are affected individuals and unaffected parents can produce affected offspring when both are carriers), II-2 could be a carrier. Her mother (I-1) is affected, implying the father (I-2) must have contributed a normal allele, and II-2, being unaffected, is most consistent with being a carrier (Aa). This aligns with the pedigree where an unaffected individual (II-2) has offspring with another unaffected individual from a related line, producing affected descendants in the next generation.
Option: Hemizygous. Hemizygosity is a term typically used for X-linked genes in males (e.g., having only one allele for a gene on the X chromosome). The trait shown here does not clearly indicate an X-linked pattern, and the pedigree includes both males and females affected/unaffected in a manner consistent with autosomal inheritance. Therefore hemizygous is not an appropriate description for II-2.
Option: Cannot be determined from the pedigree. The pedigree provides information about affected status and parental genotypes that allow reasonable deduction of II-2’s carrier status. Given I-1 is affected (aa) and I-2 must carry a normal allele at least, II-2 being unaffected points toward Aa (carrier). Thus it is not necessary to claim cannot be determined.
In summary, the option that best fits the genetic pattern shown and the phenotype of II-2 is that II-2 is heterozygous (a carrier).

Question at position 17 The genotype of individual II-2 is Homozygous dominantHomozygous recessiveheterozygoushemizygousCannot be determined from the pedigree

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