CBSE Class 10 Answered

Allele refers to one of two versions of a particular gene that is present in a diploid organism. Only one of these two is present in each of the gametes that gives rise to the organism. Dominant allele is the allele that always produces a trait. Recessive allele is the allele that only produces a trait if the dominant allele for the trait is absent.

There are two alleles of every gene, including the one for flower colour. For example a pea plant would have one allele for flower colour from its male parent and a second allele for flower colour from its female parent. The allele that confers purple flower colour may be designated P. The allele that confers white flower colour may be designated p.

In a cross between a purple-flowered plant (PP) and a white-flowered plant (pp). All gametes from the purple parent possessed the P allele while all gametes from the white parent possessed the p allele.

The offspring of this cross possess one P and one p allele (Pp). All offspring from this cross are purple since the purple trait is dominant over the white trait.

When this F1 generation is crossed, the offsprings will have 3 possible allele combinations i.e. PP, Pp, and pp. The pp combination will be white, whereas all the other combinations will be purple flower.