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Question

In F2 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
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B
One homozygous tall, one homozygous dwarf and two heterozygous tall
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C
All homozygous dwarf
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D
All homozygous tall
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Solution

The correct option is B One homozygous tall, one homozygous dwarf and two heterozygous tall
  • 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 F1 hybrid but is masked by a factor for the dominant trait and that’s why it produced both parental types in F2 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 F1 generation.
  • If dwarfism was dominant characters, it would have expressed itself in F1 generation.
  • The selfing of heterozygous tall plants yields F2 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.

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