Question

The pure tall plant is crossed to dwarf plant. F1 Generation consists of only tall plants, while F2 generation has both tall and dwarf in the ratio of 3:1. The phenomenon is due to
A) Dominance
B) Codominance
C) Incomplete dominance
D) Heredity

Answer 1

Hint: In this question we are going to find the correct option for the phenomenon. All characters are dominant in this case according to Mendel law of dominance. Thus the character is dominant when it is homozygous as well as heterozygous. If a single allele of the gene is present, it will express the phenotype.

Complete Answer:
A) Dominance: A cross between pure breeding tall (TT) and dwarf (tt) plant produces all tall hybrids (Tt). The allele that can express itself in the heterozygous individual is called the dominant factor. Here tallness is expressed in heterozygotes .Hence it is the dominant character. The other factor whose effect is masked by the presence of the dominant factor is called the recessive factor. Selfing of “Tt'' produce the phenotypic ratio of in generation which means that both homozygous dominant (TT) and heterozygous dominant (Tt) show “tall” phenotype and homozygous recessive (tt) shows “dwarf” phenotype. Hence option A is correct.

B) Codominance: codominance is when both recessive and dominant traits are expressed in a heterozygous genotype. If the trait was codominant, the heterozygote would show both tall and dwarf phenotype. Hence option B is incorrect.

C) Incomplete dominance: Incomplete dominance is the condition when none of the factors of a gene is dominant. Individuals of the phenotype of a heterozygous dominant is a blend of dominant and recessive traits. Hence option C is incorrect.

D) Heredity: Heredity is the genetic transmission of characters from parent generation to progeny. Transmission of tallness or called dwarfism is heredity but it is not the reason for appearance of tall phenotype in heterozygous or presence of ratio in generation. Hence option D is incorrect.

Hence option A: Dominance is the correct answer.

Note: According to Mendel’s law of dominance, in a cross of parents only one form of the trait will appear in the next generation. With monohybrid cross Mendel started his research by the experiments on pea plants in a variety of differing traits.