CBSE Class 10 Science 2019 · Paper 31/3/1 · Question 12(b)

${\text{F}}_1$ progeny: All the ${\text{F}}_1$ plants had round seeds; no wrinkled seeds appeared. Reason: each ${\text{F}}_1$ plant received a factor for round seeds ($\text{R}$) from one parent and a factor for wrinkled seeds ($\text{r}$) from the other, so it was $\text{Rr}$. Round is the dominant trait, so it was expressed, while wrinkled is recessive and remained hidden. ${\text{F}}_2$ progeny: When the ${\text{F}}_1$ plants were self-pollinated, both round and wrinkled seeds appeared, in the ratio of about $3$ round to $1$ wrinkled. Reason: the two factors $\text{R}$ and $\text{r}$ separate when the gametes are formed, each gamete getting only one. Random fusion of the gametes gives $\text{RR}$, $\text{Rr}$, $\text{Rr}$ and $\text{rr}$ in the ratio $1:2:1$; $\text{RR}$ and $\text{Rr}$ give round seeds and $\text{rr}$ gives wrinkled seeds, so the recessive trait reappears in one quarter of the plants. Two other contrasting characters Mendel used (any two): tall and dwarf plants; yellow and green seeds; violet (purple) and white flowers; green and yellow pods; full (inflated) and constricted pods; axial and terminal flowers.