Abbreviated genotypic ratio

Content
Lethality and Interaction of Genes
Lethality
Interaction of genes
Abbreviated genotypic ratio
Two gene pairs affecting same character
Epistasis
Complementary genes
Duplicate genes
Additional interactions involving two gene pairs
Interactions between more than two gene pairs
Modifiers, suppressors and pleiotropic genes
Meiotic drive, segregation distortion and selfish genes
Penetrance and expressivity

Depending upon the four alternatives outlined above, we can give an abbreviated genotypic ratio expected in F2 i.e. 9AB : 3Ab : 3aB : lab. In this ratio, AB means those individuals which have both A and B either in homozygous condition or in heterozygous condition (1AABB : 2AaBB : 2AABb : 4AAaBb). Similarly, Ab means absence of B, but presence of A in homozygous or heterozygous condition (1AAbb : 2Aabb). Likewise, aB includes two genotypes (1aaBB : 2aaBb) and ab will include only one genotype (1aabb).

The abbreviated genotypic ratio as outlined in summary chart shown in Table 3.1, is very useful in predicting phenotypic ratio for a particular kind of interaction. If the abbreviated genotype is understood and its use practised, no checkerboards or forked line methods will be needed for working out phenotypic ratios. In the following text some cases of interaction of genes will be discussed using only the abbreviated genotypic ratios, since checkerboard can be easily dispensed with.

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