Pedigree question (family tree)?

Question

why do you sometimes have to shade in a square (male) or circle (female)?

Answer 1

If the person exhibits the trait, you shade in the block or circle. If a person has to be a carrier in order for the offspring to exhibit the trait, you will draw line through the box or circle.

Answer 2

whether they are homozygous for a certain trait

it is half shade in when they are heterozygous for that trait