Question

In four o’clock plants, the gene for red flower colour (R) is incompletely dominant over the gene for white flower colour (r), hence the plants heterozygous for flower colour (Rr) have pink flowers. Determine the ratio of offsprings in a cross between red flowers and pink flowers.

• A. $75\% \, $ red flowers, $25\%$ pink flowers
• B. All red flowers
• C. $50\%$ red flowers, $50\%$ pink flowers
• D. Red : pink : white :: $1$ : $2$ : $1$

Answer 1

Answer: (C)

Incomplete dominance is seen in Four O' Clock plant Mirabilis jalapa.
A cross between red and pink flowers is as follows:
$Parents & RR & \times & Rr \\ & \left(\right.♂\left.\right) & & \left(\right.♀\left.\right)$

Rr

Total number of red flowers = $2$
Total number of white flowers = $2$
∴ The phenotypic ratio = $2:2$ = $1:1$
Percentage of red flowers = $\frac{2}{4}\times 100$ = $50\%$
∴ Percentage of white flowers would be = $100-50$ = $50\%$