Q. If skin colour in humans is controlled by three gene pairs, then what is the number of intermediates and parental combinations in $F_{2}$ generation?
NTA AbhyasNTA Abhyas 2020
Solution:
Polygenic inheritance is a quantitative inheritance which is controlled by two or more genes and dominant alleles of each have a cumulative effect on the character. The full trait is shown only when all the dominant alleles are present.
Human skin colour is an example of polygenic character. It has a pigment called melanin and the quantity of this pigment is determined by three pairs of polygenes (A, B & C).
Cross: Very light (aabbcc) X Very dark (AABBCC)
F1 genotype = AaBbCc
F1 phenotype = Mulatto or Intermediate
F2 genotype = $1:6:15:20:15:6:1$
F2 phenotypes = Very dark: Dark: fairly dark: intermediate: Fairly light: Light: white
The number of intermediates and parental combinations in F2 generation are 62 and 2.
Cross: Very light (aabbcc) X Very dark (AABBCC)
F1 genotype = AaBbCc
F1 phenotype = Mulatto or Intermediate
F2 genotype = $1:6:15:20:15:6:1$
F2 phenotypes = Very dark: Dark: fairly dark: intermediate: Fairly light: Light: white
The number of intermediates and parental combinations in F2 generation are 62 and 2.