Q. 15.0( 1 Vote )

In a Mendelian monohybrid cross, the F2 generation shows identical genotypic and phenotypic ratios. What does it tell us about the nature of alleles involved? Justify your answer.

Answer :

In a monohybrid cross, starting with parents which are homozygous dominant and homozygous recessive, F1 , at the same time with incomplete dominance can show identical genotypic and phenotypic ratios.

Sometimes F1 had a phenotype that did not resembled either of the two parents and was in between them.The inheritance of flower colour in dog flower is a good example


In a cross between true breeding red flowered (RR) true breeding white flowered plants (rr), the F1 was pink. When F1 was self pollinated , the F2 resulted in the following ratio 1 (RR) Red : 2 (Rr) Pink : 1 (rr) White. Here the genotype ratios were exactly as we would expect in any Mendelian monohybrid cross; but the phenotype ratio had changed from 3:1 dominant : recessive ratio. Here R was not completely dominant over r and this made it possible to distinguish Rr as pink from RR (red) and rr (white).



The genotypic and phenotypic ratios are the same as 1:2:1 in this example.


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