In the above pedigree, filled shapes indicate affected individuals. What is the most likely mode of inheritance for this pedigree? What is the most likely genotype of individual 1 (using the convention that A is the dominant allele and a is the recessive allele).

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Step into the pedigree puzzle by first noting who is affected (filled) and who isn’t (unfilled).
Option A: Dominant inheritance; aa
- If the trait were dominant, an affected individual must carry at least one dominant allele (A). An unaffected individual would be aa. Since individual 1 is unaffected (unfilled), aa is consistent for them. The presence of affected offspring when an unaffected parent (aa) mates with an affected partner can occur if the partner is Aa (or AA), producing some affected children. This makes Dominant inheritance with aa for individual 1 plausible and fits the pattern seen in the family.
Option B: Dominant inheritance; Aa
- If individual 1 were Aa, they would be affected because the dominant allele expresses the trait. But individual 1 is shown as unaffected, which contradicts Aa under a dominant model. Therefore this option is inconsistent with the pedigree.
Option C: Recessive inheritance; Aa
- If the trait were recessive, Aa individuals would be carriers and typically unaffected. However, several affected individuals exist in the pedigree, including individuals who appear as affected in multiple generations, and an unaffected parent with affected offspring is more consistent with a recessive pattern only if both parents are carriers. Yet the frequent appearance of affected individuals across generations and affected parentage here aligns better with a dominant pattern, not a simple Aa carrier scenario. This makes Recessive inheritance with Aa unlikely given the visible propagation of affected status.
Option D: Recessive inheritance; aa
- Under recessive inheritance, aa is affected and Aa or AA would be unaffected. The pedigree shows multiple affected individuals and an unaffected parent producing affected offspring, which can happen if both parents are carriers (Aa x Aa). However, in this particular diagram, the top-generation affected individuals suggest a dominant transmission rather than a strict recessive one, and the specific combination with individual 1 being unaffected and having affected children fits more cleanly with a dominant model. Thus this option is less consistent with the overall pattern.
In summary, the construction of the family shows affected individuals in a way that best aligns with a dominant mode of inheritance, and individual 1 being unaffected points to aa as their genotype under that model. Therefore, the option that matches all these considerations is the first one.

Bio 93 Section CDE 2025 Final- Section E

In the above pedigree, filled shapes indicate affected individuals. What is the most likely mode of inheritance for this pedigree? What is the most likely genotype of individual 1 (using the convention that A is the dominant allele and a is the recessive allele).

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