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Principles of Inheritance and Variation
Gene Interaction: Complementary Genes
2 question from 1 paper, each with its answer.
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Concepts tested
- Definition of complementary genes
- Modified dihybrid ratio
All Questions
2001 AIPMT 2 questions
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Ratio of complementary genes is : -Complementary genes are two non-allelic dominant genes that produce a character only when both are present together (e.g. purple flower colour in sweet pea, studied by Bateson and Punnett).
In the $F_2$ of a dihybrid cross: 9 $A\_B\_$ show the character, while 3 $A\_bb$ + 3 $aaB\_$ + 1 aabb (= 7) do not.
So the ratio is 9 : 7.
(9 : 3 : 4 is recessive epistasis and 12 : 3 : 1 is dominant epistasis.) -
Two nonallelic genes produce a new phenotype when present together but fail to do so independently then it is called : -Complementary genes are two non-allelic dominant genes that interact to produce a new phenotype only when both are present together; neither alone produces it.
Example: in sweet pea, purple flowers appear only when both C and P are present; CCpp and ccPP are both white.
Epistasis is when one gene masks the effect of another gene, and polygenes add up their effects (quantitative inheritance).
So such genes are called complementary genes.