Use Punnett squares in crosses which result in more than one genotype to work out and show the possible different genotypes

To predict the possible different genotypes resulting from genetic crosses, we can use Punnett squares. Below, I will demonstrate how to set up Punnett squares for monohybrid crosses that yield more than one genotype, specifically focusing on examples that result in both 1:1 and 3:1 phenotypic ratios.

1. Punnett Square for a 1:1 Phenotypic Ratio

Example Cross: A heterozygous tall plant (Tt) is crossed with a homozygous recessive short plant (tt).

• Alleles:
  • T = tall (dominant)
  • t = short (recessive)

Punnett Square Setup:

Results:

• Genotypes:
  • 2 Tt (tall)
  • 2 tt (short)
• Phenotypic Ratio:
  • 2 tall : 2 short or simplified to 1:1.

2. Punnett Square for a 3:1 Phenotypic Ratio

Example Cross: Two heterozygous tall plants (Tt) are crossed.

• Alleles:
  • T = tall (dominant)
  • t = short (recessive)

Punnett Square Setup:

Results:

• Genotypes:
  • 1 TT (homozygous dominant)
  • 2 Tt (heterozygous)
  • 1 tt (homozygous recessive)
• Phenotypic Ratio:
  • 3 tall (TT and Tt) : 1 short (tt), which simplifies to 3:1.

Summary of Genotypes and Ratios