The Genetics of Frizzle Frazzle Chicks


Looking for a fun lesson on genetics and deleterious alleles? Look no further than this worksheet on “frizzled” chickens!

The frizzle trait in chickens is a result of a genetic mutation that affects the feather structure. The gene responsible for the frizzle trait is known as the “F” gene. The F gene is a dominant gene, meaning that only one copy of the gene is needed for the frizzle trait to be expressed. If chicks inherit two F alleles, their feathers are brittle and fall out!

When students learn genetics, they need lots of practice setting up Punnett squares. I have several different types of practice sets, from simple to complex. I usually do the chicken genetics after “Peas, Please,” which explores Mendel’s traits. If students need extra practice, they can look at “Skinny Pigs,” which are hairless Guinea pigs.

The Inheritance Pattern for the Frizzle Allele:

FF (Homozygous Dominant): If a chicken inherits two copies of the frizzle gene (one from each parent), it will have a more extreme expression of the frizzle trait. Unfortunately, having two copies of the allele results in health problems. The feathers fall out, reducing insulation, which can be fatal.

Ff (Heterozygous): If a chicken inherits one copy of the frizzle gene from one parent and a normal feather gene (non-frizzle) from the other parent, it will still exhibit the frizzle trait. The presence of the F gene is enough to express the frizzling.

ff (Homozygous Recessive): If a chicken inherits two normal feather genes (non-frizzle), it will have normal feathering without the frizzle trait.

Furthermore, due to these potential health concerns, responsible breeders often avoid pairing two frizzle chickens with the homozygous dominant genotype (FF). Instead, they typically breed a frizzle chicken (Ff) with a non-frizzle chicken (ff) to maintain the frizzle trait while reducing the risk of health issues associated with extreme frizzling.

In this type of cross – Ff x ff, half of the offspring will show the frizzle phenotype.


The worksheet for students includes background information on the Frizzle trait and several crosses for students to complete. The crosses have the Punnett squares, but students must fill in the parent genotypes and the expected offspring combinations.

The complete curriculum for Biology, including a unit on genetics is available at Biology 2. Lecture slides and resources align to Miller and Levine Biology (Bee Book)