Fruit flies have hair-like bristles on the back of their bodies. The bristles can be long or short. Flies with short bristles have two recessive alleles (ss) for the trait.
A fruit fly that is heterozygous for the bristle trait is crossed with a fruit fly that has
short bristles. The cross produces 220 offspring.
Use a Punnett square to help calculate how many of the 220 offspring are expected
to have short bristles.