Question

A tall plant obtained by crossing a homozygous tall and dwarf plants was grown in nutrient-deficient soil. The plant remained dwarf. When this plant was crossed with a dwarf plant, then:

• A. All plants are dwarf
• B. All plants are tall
• C. 50% tall and 50% dwarf plants obtained
• D. 75% tall and 25% dwarf plants obtained

Answer 1

The correct option is C 50% tall and 50% dwarf plants obtained

First, the cross between homozygous tall $\left(TT\right)$ and the homozygous dwarf $\left(tt\right)$ plant will result in 4 tall plants with heterozygous genotype $\left(Tt\right)$. But, since they were grown in nutrient-deficient soil, they remained as dwarf plants.

These plants were then crossed with another dwarf plant $\left(tt\right)$. Such a cross is called a test cross. In this cross, 50% of plants obtained are tall, which are heterozygous dominant genotype $Tt$ (50%). There was also 50% dwarf plants, with homozygous recessive genotype $tt$. No homozygous dominant genotypes $\left(TT\right)$ were obtained.

i.e. Genotypic and phenotypic ratio is 1:1.

So, the correct option is D.