Principles of Inheritance and Variation

Deviations from Mendelian Ratios

1. Incomplete Dominance: $F_1$ hybrid shows intermediate phenotype (e.g., Mirabilis jalapa red $\times$ white $\rightarrow$ pink; phenotypic ratio $1:2:1$).
2. Codominance: Both alleles express equally in heterozygote (e.g., $I^A I^B$ genotype produces $AB$ blood group).
3. Pleiotropy: A single gene influences multiple phenotypic traits (e.g., Phenylketonuria).