Question

In Red White-flowered cross of Mirabilis jalapa, F2 generation has red, pink, and white flower plant in the ratio of
(a) 1:2:1
(b) 1:0:1
(c) 2:1:1
(d) 1:1:2

Answer 1

Hint: Incomplete dominance is a type of inheritance in which one allele for a specific trait is not completely dominant over the other allele i.e. neither allele is dominant over the other in heterozygous organisms. This results in a combined phenotype. Incomplete dominance is also called mosaic or partial dominance. Here new phenotypic characters are expressed entirely.

Complete Step by Step Answer:
- Mirabilis jalapa, the marvel of Peru commonly called as 4 o'clock plant. It is a very good example of incomplete dominance because of its Inheritance of flower color.

- Mirabilis jalapa has two types of pure breeding plants, red flowers, and white flowers. The phenotype of red flowers is considered to be as “RR” whereas the phenotype of the white flower as “rr”.When they are crossed, produce the first filial generation and all flowers possess pink color which shows blending inheritance. This clearly indicates that neither red flower nor white flower condition is dominant but when F1 generation crossed with F1 generation(on selfing them), the Second filial generation i.e. F2 generation plants show red flower, pink flower, and white flower condition in the ratio 1:2:1 i.e. RR:2Rr:rr.
- This clearly indicates the phenomenon of incomplete dominance.
So, the correct answer is, ”1:2:1”.

Additional information:
- Mirabilis jalapa is a widely cultivated ornamental plant and has great medicinal properties.
- It is cultivated in tropical and warm temperate regions of the world.
- It can reach up to 30- 70 cm in height, have thick branches and little fleshy and swollen nodes.
- Its parts used are seeds, leaves, and roots. An edible crimson dye is obtained from the flowers to color jellies and cakes.
- In Mirabilis jalapa none of the factors of a gene is dominant.

Note:
- The process of Incomplete dominance was first reported by Carl Correns in the 4 O’clock plant (commonly called Mirabilis jalapa).
- Incomplete dominance can also be seen in red and white snapdragon plants, where the resulting offspring are pink.
- The common example of incomplete dominance that occurs in humans is Tay-Sachs disease.