Question

A self pollinating plant with orange flowers and alternating leaf arrangement produces
Plants with red flowers and alternating leave- 47
Plants with orange flowers and alternating leaves- 103
Plants with yellow flowers and alternating leaves- 51

The genotype of the original parent plant is
A. Heterozygous for both flower colour and leaf arrangement
B. Homozygous for both flower colour and leaf arrangement
C. Homozygous for flower colour and heterozygous for leaf arrangement
D. Heterozygous for flower colour and homozygous for leaf arrangement
E. Heterozygous for flower colour but unable to determine genotype for leaf arrangement

Answer 1

Hint: A monohybrid cross is a cross between parents who are heterozygous for a single trait. In a monohybrid cross, the F2 generation shows the phenotypic ratio of 1:2:1 and the genotypic ratio of 3:1. This phenotypic ratio in the second generation is an example of incomplete dominance.

Complete Answer:
Plants with yellow flowers show the dominant trait of yellow colour while plants with red flowers show the recessive trait of red colour. The remaining plants with orange colour flowers show the expression of both the traits incompletely.
The leaf arrangement for plants is constantly the same which depicts the homozygous part of parent plants.

Option A- Heterozygous for both flower colour and leaf arrangement. Heterozygosity for leaf arrangement would have resulted in a different leaf arrangement in plants.

Option B- Homozygous for both flower colour and leaf arrangement. Homozygosity for both the traits would have resulted in plants with dominant traits only.

Option C- Homozygous for flower colour and heterozygous for leaf arrangement. As explained above, the result would have been opposite i.e. Dominant flower colour with different leaf arrangement.

Option D- Heterozygous for flower colour and homozygous for leaf arrangement. This option suits the situation appropriately as we discussed it above.

Option E- Heterozygous for flower colour but unable to determine genotype for leaf arrangement. As explained above, this option is incomplete.

Thus, the correct option is option D- Heterozygous for flower colour and homozygous for leaf arrangement.

Note: Incomplete dominance occurs when a dominant trait fails to completely overtake the recessive trait, thus causing a blend of both the traits in physical appearance. Examples of incomplete dominance can be seen in roses. While in codominance occurs when both the traits in genotype are seen in the phenotype. For example in ABO blood group in humans.