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  4. 1: 2: 1 phenotypic and genotypic ratio is found in :

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Q. 1 : 2 : 1 phenotypic and genotypic ratio is found in :

Delhi UMET/DPMTDelhi UMET/DPMT 2002

Solution:

When $F_{1}$ hybrid exhibited a mixture or blending of characters of two parents, the case is considered as that of incomplete or blending inheritance. For example when homozygous red flowered plants of Mirabilis jalapa (4 O clock) are crossed with homozygous white flowered plants the $F_{1}$ hybrid bears pink flower. On selfing the hybrid they show 1 : 2 : 1 phenotypic and genotypic ratio. Complementary genes are two pairs of non-allelic dominant genes which interact to produce only one phenotypic trait but neither of them produces the trait in the absence of other. Such genes which seems to behave like alleles and have minimum chance of crossing over are called pseudoalleles. Some genes may occur in more than two atclic forms i.e., a gene can mutate several times to produce several alternative expressions. Such genes are called multiple alleles.