Ans.
A monohybrid cross can be defined as 'a cross between two individuals having different copies of a chromosome or gene of interest, which is responsible for variations in a single trait.'
These variations in a single trait are controlled by two or more alleles for a single chromosomes. For example, a cross between tall pea plant and dwarf pea plant to study the inheritance of plant height.
Thus, the correct answer is 'option). they differ in a single trait.'
