Question

In 4-o'clock plants, the crossing of red-and white-flowered pure parental stocks produced pink-flowered plants. This type of genetic expression is known as
A. Dominance
B. Co-dominance
C. Incomplete dominance
D. Gene polymorphism

Answer 1

Hint: In this plant, dominant alleles cannot mask the effect of recessive alleles and the phenotype of heterozygous dominant individuals is a blend of dominant and recessive traits.

Complete answer:
When there is crossing of red and white flowered pure parental stocks in 4 o’clock plants then it produces white flowered plants because none of the factors of a gene is dominant and the phenotype of heterozygous dominant individual is a blend of dominant and recessive trait. This type of genetic expression is known as incomplete dominance.
In this plant, red flower is the dominant character whereas the white flower is recessive character and there is blending of the two alleles i.e., mixing of the alleles due to which the flower is the F1 generation will be pink in colour.
If we look at options now, option A is dominance. Dominant is that type of genetic expression where one variant of a gene on chromosome masks the effect of another gene present on the other copy of the chromosome. But here this is not the case as from crossing of red and white flowered plants, pinks flowered plants are produced which is incomplete dominance. Therefore, this option is incorrect.
Option B is Codominance. It is that type of genetic expression where the alleles of gene pairs in heterozygotes are fully expressed but here this is not the case as from crossing of red and white flowered plants, pinks flowered plants are produced which is incomplete dominance. Therefore, this option is incorrect.
Option C is Incomplete dominance. It is that type of genetic expression where the dominant alleles cannot mask the effect of recessive alleles and the example of a 4 o’clock plant is given in the question. Therefore, this option is the correct one.
Option D is Gene polymorphism. When more than one allele occupies that gene’s locus then that gene is said to be polymorphic but here this is not the case as from crossing of red and white flowered plants, pinks flowered plants are produced which is incomplete dominance. Therefore, this option is incorrect.

Hence, the correct answer is option (C).

Note: In the question, that example is given where none of the factors of gene is dominant as the pink flowered plants are formed by the crossing red flowered and white flowered plants. This type of genetic expression is termed as incomplete dominance where none of the traits is able to express.