2. Why is probability useful in biology?

Probability is the chance that a certain event will occur. For example, the probability of a head turning up on any given coin toss is 50 percent. Probability can be used to predict the chance of gametes and offspring having certain alleles.

It gives you the idea of what might happen (a mom has the allele pair Bb and dad bb; probability for the child to have the Bb allele is 50% and bb allele 50%)