Question

In F${}_2$ generation, the crossing of a homozygous tall plant with a homozygous dwarf would yield plants in the ratio of______________

• A. Two tall and two dwarf
• B. One homozygous tall, one homozygous dwarf and two heterozygous tall
• C. All homozygous dwarf
• D. All homozygous tall

Answer 1

Answer: (B)

• According to the law of dominance, a trait is represented by two contrasting factors of a gene in a heterozygous individual; the allele/factor that can express itself in a heterozygous individual is called as the dominant trait.
• The other factor whose effect is masked by the presence of the dominant factor is called recessive factor.
• The recessive factor is present in $F_1$ hybrid but is masked by a factor for the dominant trait and that’s why it produced both parental types in $F_2$ progeny.
• Owing to a dominance of tallness over dwarfism, a cross between pure breeding tall and dwarf pea plants obtains all heterozygous tall plants in $F_1$ generation.
• If dwarfism was dominant characters, it would have expressed itself in $F_1$ generation.
• The selfing of heterozygous tall plants yields $F_2$ generation with the genotypic ratio of 1 TT (homozygous tall): 2 Tt (heterozygous tall): 1 tt (homozygous dwarf). Thus, the correct answer is option B.