Question

A dihybrid tall plant bearing yellow flowers was crossed with a dwarf plant bearing white flowers. What is the percentage of progeny expected to be homozygous tall bearing yellow flowers?
A. 0%
B. 25%
C. 50%
D. 75%

Answer 1

Hint:- The genetic condition in which an organism is carrying the same allele that bears the same phenotypic expression is called homozygous. When an individual carries a phenotypically different allele, and possesses dominance, and receives character between them is called heterozygous.

Complete step-by-step solution:- In the given question, a dihybrid tall plant with yellow flowers is crossed with a dwarf plant with white flowers.
Let the genotypic expression of a hybrid tall plant with yellow flowers be TtYy. Here T stands for tall character and the yellow flower is represented by Y.
The genotypic expression of the dwarf plant with white flowers will be ttyy. Here t refers to the dwarf character and y is representing the white flowers.
T is dominant over t and Y is dominant over y. Thus in heterozygous conditions (Tt/ Yy) the dominant character will be expressed phenotypically.

| TY| Ty| tY| ty
---|---|---|---|---
ty| TtYyTall yellow| TtyyTall white| TtYyTall yellow| ttyyDwarf white
ty| TtYyTall yellow| TtyyTall white| TtYyTall yellow| ttyyDwarf white
ty| TtYyTall yellow| TtyyTall white| TtYyTall yellow| ttyyDwarf white
ty| TtYyTall yellow| TtyyTall white| TtYyTall yellow| ttyyDwarf white

In this cross, 50% heterozygous tall plant with yellow flowers is found.
25% heterozygous tall with white flower is found
a 25% dwarf plant with white flowers is found.
The percentage of having a homozygous tall plant with yellow flowers will be 0.

Note:- To know the actual genotypic expression, always a homozygous recessive is chosen to cross with that individual. This cross is called the test cross. In the dihybrid cross, the phenotypic ratio is always 1:1:1:1. The same ratio is found in the given cross. So it can be concluded that here the test cross is done.