10 (a) Purebred and Hybrid  p80

Mendel decided to cross plants with contrasting traits—for example, tall plants and short plants. He started his experiments with purebred plants. A purebred organism is the offspring of many generations that have the same trait. For example, purebred short pea plants always come from short parent plants.

In pea plants, the allele for tall stems is dominant over the allele for short stems. Pea plants with one allele for tall stems and one allele for short stems will be tall. The allele for tall stems masks the allele for short stems. Only pea plants that inherit two recessive alleles for short stems will be short.


Only pea plants that inherit two recessive alleles for short stems will be short.

A hybrid (hy brid) organism has two different alleles for a trait. Pea plants with one allele for tall stems and one allele for short stems will be tall. All the F1 plants are tall because the dominant allele for tall stems masks the recessive allele for short stems.

When Mendel crossed the F1 plants, some of the offspring in the F2 generation inherited two dominant alleles for tall stems. These plants were tall. Other F2 plants inherited one dominant allele for tall stems and one recessive allele for short stems. These plants were also tall. The rest of the F2 plants inherited two recessive alleles for short stems. These plants were short.