In tomato plants, stem colour is determined by a single gene with two alleles. The allele for purple stems is dominant over the allele for green stems.
A researcher crossed homozygous purple-stemmed tomato plants with homozygous green-stemmed tomato plants. All of the offspring (F1 generation) had purple stems.
Use a genetic diagram to show the parent genotypes, the gametes formed, and the genotypes of the F1 offspring. Use AAA to represent the allele for purple stems and aaa to represent the allele for green stems.
The researcher then ensured that the F1 offspring plants could only self-pollinate. The seeds produced grew to give F2 plants with a 3:13 : 13:1 phenotypic ratio of purple-stemmed to green-stemmed plants. Suggest how the researcher could ensure that these tomato plants self-pollinated and were not cross-pollinated by other plants.
Give the genotypes of the F2 offspring obtained from the self-pollinated F1 plants.
What is meant by the term recessive allele?
Some phenotypes are controlled by codominant alleles. What is meant by the term codominant alleles?
