Question

The phenotypic ratio of incomplete dominance is
A) 2:1
B) 1:2:1
C) 1:1:1
D) 1:1:2

Answer 1

Dominance is defined as the condition where between the two different alleles present in an individual one is expressed which is the dominant allele and the expression of the other allele is repressed which is the recessive allele.

Complete answer:
Dominance is a concept of mendelian inheritance but incomplete dominance is deviation from mendelian genetics. Incomplete dominance is also known as partial dominance or semi- dominance. In case of incomplete dominance the dominant allele does not completely mask the effect of the recessive allele, instead there is a blending of both the dominant allele and the recessive allele that ultimately affects the phenotype of the organism.

The phenotypic ratio of incomplete dominance in the first filial generation is 1:2:1. Incomplete dominance is mostly explained in snapdragon flower by crossing a red flower with a white flower, where red is the dominant allele and white is the recessive allele. If red is completely dominant over red then most of the offspring of the first generation will have red colour, but instead offspring are found to have pink colour which is produced as a result of blending the red and white colour.

Hence the correct answer is option (B) 1:2:1.

Note: Another kind of deviation from mendelian genetics is codominance. Codominance is different from incomplete dominance since in codominance the products of both the alleles exist together whereas in incomplete dominance there is interaction between the two allelic products leading to a new phenotype.