Simple Genetic Cross Example Using Punnett Squares

Learn more about Punnet Squares here:    • Punnett Square Basics | Mendelian Gen...  

Learn more about Alleles here:    • Homozygous vs Heterozygous Alleles | ...  

Learn more about Genotypes and Phenotypes here:
   • Genotype vs Phenotype | Understanding...  

Let’s solve a simple genetic cross using a Punnett square.

In rabbits, coat color is determined by a single gene with two alleles: uppercase B (brown coat) and lowercase b (white coat). A homozygous dominant brown-coated rabbit (BB) is crossed with a homozygous recessive white-coated rabbit (bb). Determine the possible genotypes and phenotypes of their offspring.

To start, let’s set up our Punnett square. We will put the brown-coated rabbit alleles across the top. Both uppercase B.

And the white-coated rabbit on the side. Both lowercase b.

Now we match up the alleles in their corresponding squares. In this case, every square gets one big B and one little b.

So these are the possible outcomes, and the question asked for the possible genotypes and phenotypes.

Genotypes are the alleles, which are 100% heterozygous, big B and little b.

The phenotype refers to the expression of the genes. Given that there is only one genotype, we only have one phenotype, brown-coated rabbits.