A monohybrid cross and a dihybrid cross are two types of genetic crosses that study how traits are inherited in offspring, but they differ in the number of traits studied at one time.
Here’s the difference explained :
- Monohybrid cross
- A monohybrid cross studies one trait at a time.
- The parents differ in one pair of contrasting traits (for example, tall vs. short plants).
- It shows how a single gene with two alleles is inherited.
- The F₂ generation (second generation) shows a 3:1 ratio — three with the dominant trait and one with the recessive trait.
- Example:
Crossing a tall pea plant (TT) with a short pea plant (tt) produces all tall F₁ plants (Tt). When F₁ plants self-pollinate, the F₂ generation shows tall and short plants in a 3:1 ratio.
- Dihybrid cross
- A dihybrid cross studies two traits at the same time.
- The parents differ in two pairs of contrasting traits (for example, seed color and seed shape).
- It shows how two genes are inherited together and whether they assort independently.
- The F₂ generation shows a 9:3:3:1 ratio — nine with both dominant traits, three with one dominant and one recessive trait, three with the other dominant and one recessive trait, and one with both recessive traits.
- Example:
Crossing a pea plant with round yellow seeds (RRYY) and one with wrinkled green seeds (rryy) gives all F₁ plants with round yellow seeds (RrYy). When F₁ plants self-pollinate, the F₂ plants show four combinations in a 9:3:3:1 ratio.
In summary:
- Monohybrid cross → studies one trait → 3:1 ratio.
- Dihybrid cross → studies two traits → 9:3:3:1 ratio.
Both help explain how traits are passed from parents to offspring, following Mendel’s laws of inheritance.