Question

Mendel bred a purple-flowered pea plant with a white-flowered pea plant and found that all the offspring had purple flowers. But then when he bred together two of the purple-flowered offspring, some of their offspring had white flowers. Using the concepts of dominant and recessive alleles, explain how the trait of white flowers skipped a generation.

Answer 1

Mendel's crosses of purple and white-flowered pea plants showed that the purple flower trait is dominant. F₁ offspring were all purple because they were heterozygous (Pp), but in the F₂ generation, white flowers reappeared due to the law of segregation where some offspring were homozygous recessive (pp).

Step-by-step explanation:

When Mendel crossed purple-flowered pea plants with white-flowered pea plants, he observed that all the F₁ offspring had purple flowers. This phenomenon occurred because the purple flower trait is dominant over the recessive white flower trait. These F₁ plants had one purple flower allele (P) and one white flower allele (p), making them heterozygous (Pp). However, when these F₁ purple-flowered plants were crossed together, the F₂ generation exhibited both purple and white flowers. This happened because each F₁ plant could pass either a P or p allele to its offspring. The appearance of white flowers in the F₂ generation can be explained by the law of segregation, which states that the two alleles for a trait separate during the formation of gametes. Therefore, the white flower trait did not really skip a generation, it was just not expressed in the F₁ because the dominant purple allele masked it. In the F₂ generation, when some offspring received a recessive allele (p) from each parent, they displayed white flowers as they were then homozygous recessive (pp).

Answer 2

Purple is dominant to white flowered.
Purple gene(which occurs in pairs of PP which are both dominant alleles) crossed with a recessive pp(white flowered) after crossing, all the offspring had Pp. Purple being dominant suppressed the white(p).
after crossing the offspring, (Pp and Pp) a quarter the offspring lacked the dominant allele P hence allowing the recessive colour white to be shown.