Question

This pedigree chart tracks the inheritance of a recessive trait that is not sex-linked. Based on the information in the chart, which of the following statements is true?
Individual #11 must be homozygous for the recessive trait.

Individuals #3 and #4 must be heterozygous for the trait.

Individual #2 must be heterozygous dominant for the trait.

Individual #9 must be homozygous dominant for the trait.

Answer 1

The first thing to realize is that the trait is recessive. That means that individuals only express the trait when they don't have even a single dominant allele for that gene - that is, when they are homozygous recessive. So the genotypes of all the affected (shaded) individuals you know: they are homozygous recessive.

Once you have that, you can start crossing off the options it can't be. For example, you know that 11 cannot be homozygous recessive for the trait, otherwise he would express the trait.