CBSE Class 10 Science 2022 · Paper 31(B)/5 · Question 14

(a) Any two of: round and wrinkled seeds; yellow and green seeds; violet and white flowers; axial and terminal flowers; inflated (full) and constricted pods; green and yellow pods (for example, round/wrinkled seed shape and violet/white flower colour). (b) Every $F_1$ plant received $T$ from the tall parent and $t$ from the short parent, so all were $Tt$. Tallness is the dominant trait: a single $T$ makes the plant tall, and the recessive trait (shortness) does not show when $T$ is present. So only tall plants appeared in $F_1$. (c)(i) $Tt\times Tt$ gives $TT:Tt:tt=1:2:1$, that is $3$ tall : $1$ short. Of the $1600$ plants, (I) tall $=\frac{3}{4}\times 1600=1200$ and (II) short $=\frac{1}{4}\times 1600=400$ (expected numbers). The gene combinations in $F_2$ are $TT$, $Tt$ and $tt$ in the ratio $1:2:1$, that is about $400$ $TT$ (tall), $800$ $Tt$ (tall) and $400$ $tt$ (short). OR (c)(ii) Yes. If the same kind of cross in other angiosperms gives similar results, the student can conclude that in those plants, too, each trait is controlled by a pair of factors (genes), one from each parent; that one trait of a contrasting pair is dominant and shows in $F_1$ while the other is recessive and stays hidden; and that the factors separate when gametes are formed, so the recessive trait reappears in $F_2$, in about one plant in four ($3:1$). The rules of inheritance found in the pea hold for these plants as well.