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Principles of Inheritance and Variation
Inheritance of Three Genes
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Concepts tested
- Gametes and zygotes in a trihybrid cross
All Questions
2004 AIPMT 1 question
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A self-fertilizing trihybrid plant forms :-A trihybrid plant is heterozygous for three genes, e.g. AaBbCc.
Number of types of gametes $= 2^n$, where n is the number of heterozygous gene pairs: $2^3 = 8$ (ABC, ABc, AbC, Abc, aBC, aBc, abC, abc).
On self-fertilisation, each of the 8 types of male gametes can fuse with each of the 8 types of female gametes.
Number of zygote combinations $= 8 \times 8 = 64$ (the squares of the Punnett square).
(These give 27 different genotypes and 8 phenotypes in the ratio 27 : 9 : 9 : 9 : 3 : 3 : 3 : 1.)
So the plant forms 8 different gametes and 64 different zygotes.