Question

How would you test a pea plant whether it is pure or hybrid for tallness?
a) Cross it with another tall pea plant of unknown genotype
b) Cross it with a pure tall pea plant
c) Cross with a homozygous dwarf pea
d) Cross it with any pea plant

Answer 1

The crossing of the pea plant was first done by Mendel. It was done to determine whether the traits of the parents were transferred to the offspring or not. He used seven visible traits of the pea plants which also included the tallness and dwarfness of the plant.

Complete answer:
The tallness trait of the pea plant may have a homozygous or heterozygous genotype. The dwarf plant has a homozygous genotype. In order to determine whether the pea plant is homozygous tall or heterozygous tall, it needs to be crossed with the dwarf plant. In this type of cross if the offspring appears to be all tall then we can say that the parent pea plant was homozygous in nature. If the cross between the dwarf and tall pea plants yields equal amounts of tall and dwarf offspring then we can say that the tall plant had heterozygous genotype. So, in order to determine the genotype of the pea plant, we should cross it with a homozygous dwarf plant.

Additional information:
-If the pea plant is crossed with another tall pea plant then it will yield only tall pea plants as both the homozygous and heterozygous genotypes will give tall pea plants.
-if the pea plant is crossed with any pea plant then it can lead to results which we would not expect and we would not be able to determine whether the tall pea plant would be pure or hybrid in nature.

So, the answer is ‘cross with a homozygous dwarf pea’.

Note: The pea plant which is tall in nature but has an unknown genotype can be crossed with the dwarf plants in order to determine the unknown genotype. If the plant is pure then the offspring will be only tall and if the hybrid pea plant is crossed then it will yield both dwarf and tall pea plants.