What is the term for a cross between plants that differ in only one characteristic?

• A. Back cross
• B. Dihybrid cross
• C. Two-factor cross
• D. Monohybrid cross

Answer: (D)

This is a monohybrid cross: a cross between organisms that differ in only one trait. In monohybrid crosses you examine one gene that has two alleles, such as tall versus short height, while keeping all other traits the same. If the parents are true-breeding for opposite versions of that trait, their offspring (the F1 generation) will all display the dominant trait. When those F1 individuals are crossed, the next generation (the F2) typically shows a 3:1 ratio of dominant to recessive phenotypes, reflecting the segregation of alleles described by Mendel. This differs from crosses that involve two traits at once (a dihybrid or two-factor cross) or a back cross, which involves crossing an F1 back to a parental genotype.