CBSE 2024 · Region 3 · Set 1 · Q24 · 3 marks
Three crosses were carried out in pea plants with respect to flower colour violet/white (V/v) and flower position axial/terminal (A/a). Study in the table the crosses 'a', 'b' and 'c' where parental phenotypes and their $\displaystyle \mathrm{F}_{1}$ progeny phenotypes are given. Parental plants (Phenotypes) $\displaystyle \mathrm{F}_{1}$ Progeny (Phenotypes) (a) Violet, axial × white, axial $\displaystyle 6$/$\displaystyle 16$ white, axial $\displaystyle 2$/$\displaystyle 16$ white, terminal $\displaystyle 6$/$\displaystyle 16$ violet, axial $\displaystyle 2$/$\displaystyle 16$ violet, axial (b) Violet, axial × white, terminal $\displaystyle 1$/$\displaystyle 4$ violet, axial $\displaystyle 1$/$\displaystyle 4$ violet, terminal $\displaystyle 1$/$\displaystyle 4$ white, axial $\displaystyle 1$/$\displaystyle 4$ white, terminal (c) Violet, axial × violet, axial $\displaystyle 3$/$\displaystyle 4$ violet, axial $\displaystyle 1$/$\displaystyle 4$ white, axial
Find the genotypes of each of the parental pairs of crosses 'a', 'b' and 'c'.
| Parental plants (Phenotypes) | $\displaystyle \mathrm{F}_{1}$ Progeny (Phenotypes) |
| (a) Violet, axial × white, axial | $\displaystyle 6$/$\displaystyle 16$ white, axial $\displaystyle 2$/$\displaystyle 16$ white, terminal $\displaystyle 6$/$\displaystyle 16$ violet, axial $\displaystyle 2$/$\displaystyle 16$ violet, axial |
| (b) Violet, axial × white, terminal | $\displaystyle 1$/$\displaystyle 4$ violet, axial $\displaystyle 1$/$\displaystyle 4$ violet, terminal $\displaystyle 1$/$\displaystyle 4$ white, axial $\displaystyle 1$/$\displaystyle 4$ white, terminal |
| (c) Violet, axial × violet, axial | $\displaystyle 3$/$\displaystyle 4$ violet, axial $\displaystyle 1$/$\displaystyle 4$ white, axial |
Marking-scheme solution
(a)
Parental genotype is not possible to find from the given information.
(b)
Violet, axial × White, terminal
Parents are heterozygous dominant × homozygous recessive.
VvAa × vvaa
(c)
Violet ,axial × Violet, axial
heterozygous for flower colour and homozygous dominant for flower position
VvAA × VvAA
Principles of Inheritance and VariationInheritance of Two GenesAnalyseshort_answerhard
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CBSE Class 12 Biology past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.