Question

A white flowered Mirabilis plant (rr) was crossed with red coloured plant (RR). If 120 plants are produced in F2 generation, the result would be

• A. 90 uniformly coloured and 30 white
• B. 90 Non-uniformly coloured and 30 white
• C. 60 Non-uniformly coloured and 60 white
• D. All coloured and No white
• E. 30 red coloured, 60 non-uniformly coloured and 30 white

Answer 1

The correct option is E 30 red coloured, 60 non-uniformly coloured and 30 white

Mirabilis plant shows incomplete dominance of flower colour. It means that one allele for the flower colour is not completely dominant over the other one and thus, the heterogenous genotype shows a combination of dominant and recessive phenotypes. A cross between white flowered (rr) and red flowered plant (RR) gives all plants non-uniformly coloured flowers (Rr). Self fertilization of this heterogenous plants yields plants with red, non-uniformly coloured and white coloured flowers in 1 : 2 : 1 ratio respectively. Hence, out of total 120 plants, the ratio of red, non-uniformly coloured and white flowered plants will be 30 : 60 : 30.

Thus, the correct answer is option E.