Question

In snapdragon (Antirrhinum majus), a plant with red flowers was crossed with a plant with white flowers. Work out all the genotypes and phenotypes of F1 and F2 generations. Comment on the pattern of inheritance in this case.

Answer 1

Hint:In partial dominance, a dominant allele or gene does not completely mask the effect of the recessive gene which results in the blending of both alleles. This phenomenon results in the formation of a heterozygous individual.

Complete answerSnapdragon or dog flower, when a true-breeding red-flowered plant with genotype RR is crossed with true-breeding white-flowered plants with genotype rr, then a heterozygous pink-flowered plant with genotype Rr is produced. In this case, the dominant allele does not completely mask the effect of the other allele which results in the generation of a heterozygous phenotype. The cross produces a pink-flowered plant and this is a form of intermediate inheritance. The pink-flowered plants are produced as a result of phenotypic blending because there is no actual blending of alleles or genetic material. This phenomenon is known as incomplete inheritance.

Note: Cross-pollination between red snapdragons and white snapdragons result in the production of pink snapdragons when neither the white or red alleles are dominant. This is an example of incomplete dominance. In this type of inheritance, both dominant and recessive alleles have partially expressed that result in intermediate inheritance. It is also known as semi-dominance, or it can be said as partial dominance. It shows the blending of genes or phenotypic characteristics.