Question

In Mirabilis jalapa, a red-flowered plant was crossed with a white-flowered plant, which resulted in all pink-flowered plants.

What are the chances of the appearance of red-flowered plants in a cross between pink-flowered and white-flowered plants?

• A. 25%
• B. 50%
• C. 75%
• D. 0%

Answer 1

The correct option is D 0%

The red and white-flowered plants of Mirabilis jalapa exhibit incomplete dominance in the inheritance of flower colour, due to which they produce pink-flowered plants upon hybridisation.

If pure breeding red-flowered plants are represented as ‘RR’ and pure breeding white-flowered plants as ‘rr’, then the pink-flowered plants are ‘Rr’.

A cross between ‘Rr’ and ‘rr’ would produce pink-flowered plants (Rr) and white-flowered plants (rr) in the ratio of 1 : 1

Hence, there are zero chances of getting a red-flowered plant.

Parents: Rr (Pink) X rr (White)
Gametes: R r r
$\begin{array}{ccc}& \text{R}& \text{r}\\ \text{r}& \text{Rr (Pink)}& \text{rr (White)}\end{array}$