Question

For Mendel's pea plants, the tall phenotype is determined by a dominant allele and the dwarf phenotype is determined by a recessive allele. Suppose there is a cross between true-breeding tall and true-breeding dwarf plants. What is the expected outcome in the second or F3 generation when F1 plants are crossed to each other?

Answer 1

Crossing F1 heterozygous tall pea plants (Tt) with each other yields an F2 generation with a 3:1 phenotypic ratio of tall to dwarf plants. This can be predicted using a Punnett square, revealing genotypes of TT, Tt, Tt, and tt.

Step-by-step explanation:

When working with Mendel's pea plants, a true-breeding tall plant has a genotype TT, and a true-breeding dwarf plant has a genotype tt. The outcome of crossing a true-breeding tall (TT) plant with a true-breeding dwarf (tt) plant results in F1 generation offspring that are all heterozygous (Tt) and tall, as the tall trait is dominant. When these F1 heterozygous plants are crossed with each other, the expected outcome in the F2 or third-generation (assuming F1 is considered the second-generation following the parental, or P, generation) can be predicted using a Punnett square which reveals a phenotypic ratio of approximately 3:1, tall to dwarf plants. This is because the F1 plants have a 1/4 chance of producing offspring with two dominant alleles (TT), a 1/2 chance of producing offspring with one dominant and one recessive allele (Tt), and a 1/4 chance of producing offspring with two recessive alleles (tt).

The Punnett square analysis, an important tool in genetics, would show the following genotypes for the F2 generation: TT, Tt, Tt, and tt. From these genotypes, the phenotypes would be tall (TT or Tt) and dwarf (tt).