
Concept explainers
When Mendel did crosses of true-breeding purple- and white-flowered pea plants, the white-flowered trait disappeared from the F1. generation but reappeared in the F2 generation. Use genetic terms to explain why that happened.

To explain: Why the white color trait disappeared in the F1 generation and was again observed in the F2 generation in Mendel’s cross between purple- and white- flowered pea plants.
Introduction: Genes have alternate forms known as alleles, which are transmitted to offspring. If the two alleles are different, then there is a hybrid in the F1 generation. The dominant allele out of the two expresses itself and determines the phenotype. In F1 individuals, two different alleles segregate into gametes. During self-pollination, the gametes unite randomly, thereby giving a chance to recessive alleles to be expressed in a homozygous state at the F2 generation.
Explanation of Solution
The cross between the individuals that are true breeding homozygous for one allele gives different traits in F1 progeny. This is called as monohybrid cross. Several traits of pea plants were studied in which Mendel used the purple- and white-colored flower traits to perform monohybrid experiment. When Mendel crossed these plants, the F1 hybrids or first true breeding generation received was both dominant and recessive alleles equally but showed a purple pigment. This is because the purple-colored trait was dominant over white. That is, white-colored trait is and was not expressed recessive in the F1 generation. However, the white trait was expressed in F2 generation of the experiment. This was because it is only possible for a white allele to exist in a homozygous state, which causes the white trait to be expressed in F2 generation.
Pictorial representation: Fig.1 shows Mendel’s cross between purple- and white-flowered pea plants.
Fig.1: Mendel’s cross between purple- and white-flowered pea plants
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