Question

Which type of cross is used to determine the genotype of tall pea plant? Explain.

Hint:

A test cross is always done with a recessive parent to determine the unknown genotype of the dominant phenotype.

Answer 1

The type of cross used to determine the genotype of a tall pea plant is called a Test Cross. Explanation: - A tall pea plant may have either of the two genotypes: \[\begin{array}{rl} \bullet & \text{Homozygous dominant (TT)} \\ \bullet & \text{Heterozygous (Tt)} \\ \end{array}\] - To find out whether the tall plant is TT or Tt, it is crossed with a homozygous recessive dwarf plant (tt). Case 1: If the tall plant is TT (homozygous) \[ TT \times tt \;\; $\Rightarrow$ \;\; 100% \; Tall (Tt) \] All offspring will be tall. Case 2: If the tall plant is Tt (heterozygous) \[ Tt \times tt \;\; $\Rightarrow$ \;\; 50% \; Tall (Tt) \; & \; 50% \; Dwarf (tt) \] Conclusion: - If all progeny are tall → the parent tall plant is homozygous (TT). - If progeny are 50% tall and 50% dwarf → the parent tall plant is heterozygous (Tt).