CBSE Class 10 Science 2022 · Paper 31/1/1 · Question 5(b)

Heredity 2 marks Medium

(i)In a cross between violet flowered plants and white flowered plants, state the characteristics of the plants obtained in the $F_{1}$ progeny.
(ii)If the plants of $F_{1}$ progeny are self-pollinated, then what would be observed in the plants of $F_{2}$ progeny ?
(iii)If 100 plants are produced in $F_{2}$ progeny, then how many plants will show the recessive trait ?

Answer

All $F_{1}$ plants are violet (Vv); $F_{2}$ gives violet : white = 3 : 1; 25 of 100 plants show the recessive white trait.

(i) All the

F_{1}

plants have violet flowers; no white-flowered plant appears. Violet is the dominant trait. Each

F_{1}

plant is a hybrid,

V v

: it carries the factor for white flowers but does not show it. (ii) In the

F_{2}

progeny both violet-flowered and white-flowered plants appear, in the ratio 3 violet : 1 white; the white (recessive) trait, hidden in

F_{1}

, reappears. The genotypes are in the ratio

1 V V : 2 V v : 1 v v

. (iii) One quarter of the

F_{2}

plants show the recessive trait:

\frac{1}{4} \times 100 = 25

plants, with white flowers.

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