Question

In pea plants, tall stem trait (T) is dominant over the dwarf stem trait (t). A cross involving homozygous tall and homozygous dwarf plants produce tall plants. If the $F_1$ tall plants are interbred, their progeny consists of

• A. Only tall plants
• B. Only dwarf plants
• C. Both tall and dwarf plants in the ratio of 1 : 1
• D. Both tall and dwarf plants in the ratio of 3 : 1

Answer 1

Answer: (D)

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 the heterozygous individual is called as a dominant trait. The other factor whose effect is masked by the presence of the dominant factor is called recessive factor. Thus, a cross between pure breeding tall (TT) and dwarf (tt) pea plants will obtain all hybrid tall (Tt) offspring in F${}_1$ generation. According to the law of segregation, the two factors for a trait, present together in heterozygous tall plants, 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 (T) and 50% carry the recessive factor (t). Random fusion of these gametes from two-hybrid tall plants produces tall and dwarf F${}_2$ plants in a 3:1 ratio.

So, the correct answer is option D.