Question

Pink flowered progeny of red and white flowered parents of Antirrhinum majus is produced due to

• A. Dominance
• B. Epistasis
• C. Codominance
• D. Incomplete dominance

Answer 1

Answer: (D)

Incomplete dominance

Incomplete dominance is the condition when none of the factors of a gene is dominant and the phenotype of a heterozygous dominant individual is a blend of dominant and recessive traits. For example, flower colour in Antirrhinum majus shows incomplete dominance and the monohybrid cross between two pure varieties gives 1 red : 2 pink : 1 white phenotypic ratio in F${}_2$ generation. Here, the heterozygous genotypes show the blending of dominant and recessive phenotypes. Epistasis is the non-allelic gene interaction where the presence of one gene masks the expression of another gene; it is an attribute of polygenic trait while flower colour in Antirrhinum majus is controlled by a single gene; option B is wrong. As we know that, a trait is represented by two contrasting factors of a gene in a heterozygous individual; the allele/factor that can express itself in a heterozygous individual is called as a dominant trait. The other factor whose effect is masked by the presence of dominant factor is called as the recessive factor. A cross between pure breeding dominant and recessive varieties produces all dominant varieties which are not the case in flower colour in Antirrhinum majus; option A is incorrect. When both recessive and dominant traits are expressed in a heterozygous genotype; it is codominance; but in Antirrhinum majus, a new blending trait is expressed in heterozygous genotype, option C is incorrect.