Principles of Inheritance and Variation Question 33
33. $F_2$ generation in a Mendelian cross showed that both genotypic and phenotypic ratios are same as $1: 2: 1$. It represents a case of: [2012]
(a) Co-dominance
(b) Dihybrid cross
(c) Monohybrid cross with complete dominance
(d) Monohybrid cross with incomplete dominance
Show Answer
Answer : d
Hints & Solution
(d) Incomplete (partial or mosaic) dominance is the phenomenon where none of the two contrasting alleles or factors is dominant. The expression of the character in a hybrid or $F_1$ individual is intermediate or a fine mixture of the expression of the two factors (as found in homozygous state). Incomplete or mosaic inheritance is not an example of pre-Mendelian concept of blending inheritance because the parental types reappear in the $F_2$ generation. It is however, considered by some workers to be an example of quantitative inheritance where only a single gene pair is involved. $F_2$ phenotypic ratio is $1: 2: 1$, similar to genotypic ratio. Pink snapdragons are a result of incomplete dominance. Cross-pollination between red snapdragons and white snapdragons result in pink when neither the white or the red alleles are dominant. The fruit color of eggplants is another example of incomplete dominance.
