CBSE Class 10 Science 2017 · Paper 31/1/C · Question 18

Heredity 3 marks Medium

If we cross-bred tall (dominant) pea plant with pure-bred dwarf (recessive) pea plant, we will get plants of

F_{1}

generation. If we now self-cross the pea plant of

F_{1}

generation, we obtain pea plants of

F_{2}

generation.

(i)What do the plants of $F_{1}$ generation look like ?
(ii)State the ratio of tall plants to dwarf plants in $F_{2}$ generation.
(iii)State the type of plants not found in $F_{1}$ generation but appeared in $F_{2}$ generation. Write the reason for the same.

Answer

$F_{1}$ plants are all tall; $F_{2}$ tall : dwarf $= 3 : 1$ ; dwarf plants reappear when two gametes carrying $t$ fuse.

(i) All the plants of the

F_{1}

generation are tall (genotype Tt); none of them is dwarf. (ii) The ratio of tall plants to dwarf plants is

3 : 1

(the genotypes TT, Tt and tt are in the ratio

1 : 2 : 1

). (iii) Dwarf plants. The

F_{1}

plants are Tt: they carry the recessive factor t for dwarfness, but it does not show because the dominant factor T masks it. When the

F_{1}

plants are self-crossed, the two factors separate into different gametes, and when two gametes carrying t fuse, the offspring is tt, which is dwarf. So the recessive trait, hidden in

F_{1}

, reappears in about one-fourth of the

F_{2}

plants.

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CBSE Class 10 Science 2017 · Paper 31/1/C · Question 18

Answer

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