Fill in the genotypes for all 10 individuals on the pedigree attached. Use the letter A. This trait follows normal dominance rules. Aa shows the dominant trait.

Question

Fill in the genotypes for all 10 individuals on the pedigree attached. Use the letter A. This trait follows normal dominance rules. Aa shows the dominant trait.

Answer 1

The key to pedigree analysis is to look for patterns in the chart that either are consistent with certain modes of inheritance, or would rule out modes of inheritance.Analysis is based on reasoning about what could or could not happen with dominant and recessive alleles, and what could or could not happen with autosomal or x-linked inheritance. It does not use ratios like classical Mendelian analysis because the number of offspring are far too small to be statistically significant, even with a very large pedigree chart

In this example, let's start by considering that individuals 1 and 2, who do not have the condition, have a daughter who does have the condition. The result of two unaffected parents who have an affected child is a clear indication the trait is tdue to a recessive allele. This also cannot be x-linked, because in order for the daughter to have the trait, the father would also have to have it if this were x-linked. That is because he would only have one x chromosome, and it would have to have the recessive allele to be passed on to the daughter.

The same situation also occurs with individuals 4 and 5, both unaffected, but they have an affected daughter, so this is consistent with the trait being autosomal recessive.

That means individuals 1 and 2 must be heterozygous (Aa), and that would also be true for individuals 4 and 5. All the shaded squares and circles represent individuals who are homozygous recessive (aa). Those would be individuals 3, 6, 7 and 9. So that just leaves individuals 8 and 10. We know that individual 8 must be heterozygous (Aa) because she has an affected daughter, meaniong that she must carry one copy of the recessive allele, and one dominant copy since she is unaffected. For the remaining individual, 10 she must have at least one dominant allele, but there is no way to know based on this chart what the other allele might be. We could calculate a 2/3 probability the she is heterozygous, and a 1/3 chance that she is homozygous dominat, but with no way of knowing which it actually is, her genotype should be written as A_. The underscore for the second allele indicates the ambiguity.

Hope this helps