Question

If a plant is heterozygous for tallness, the $F_2$ generation has both tall and dwarf plants. This proves the principle of

• A. Dominance
• B. Segregation
• C. Independent assortment
• D. Incomplete dominance

Answer 1

The correct option is B Segregation

• According to the law of dominance, a trait is represented by two contrasting factors of a gene in a heterozygous individual; only dominant trait is expressed, irrespective of the presence of both factors, in a heterozygous individual. It does not tell about the reappearance of the missing trait in $F_2$ generation.
• The law of segregation states that the two factors for a trait, present together in a heterozygous individual, do not get mixed and are separated during gametogenesis.
• Thus each gamete receives one allele for a trait and two types of gametes are formed; 50% gametes carry factor for dominance and 50% carry the recessive factor.
• Random fusion of these gametes leads to the presence of both recessive and dominant individuals in $F_2$ generation. Law of independent assortment tells about segregation and distribution of factors governing two different traits; not about segregation of factors of one trait.
• Incomplete dominance is the condition when none of the factors of a gene is dominant and the phenotype of a heterozygous dominant individual is a blend of dominant and recessive traits. It affects the phenotype of $F_1$ individuals, not that of $F_2$. Thus, the correct answer is option B.