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  2. Question
  3. Biology
  4. 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.

Q. 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.

NTA AbhyasNTA Abhyas 2020 Report Error

Solution:

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 = $100-50$ = $50\%$

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