The combs of chickens are controlled by four alleles, which interact to produce four distinct phenotypes: single, rose, pea, and walnut.

In this exercise, students predict the outcomes of chicken crosses. Ideally, students should already know how to do crosses that involve two traits, the mechanisms for solving these problems are similar.

My honors biology (AP Biology) students are encouraged to use mathematically probability to solve crosses that involve multiple traits. Punnett squares become unwieldy when multiple alleles are involved.

Many of the questions can be solved visually, without using math or a Punnett square. For example the cross rrpp x RRPP will always produce chickens with the genotype RrPp, which will have walnut combs.

For more information on the genetics of chicken combs: