Junior Class 1 Answered

Hi Bhuwana,

Monohybrid Cross

Mendel first carried out cross breeding by taking only one character.

Example: Pure tall (TT) pea plant was crossed with dwarf (tt) plant.

• F₁ Generation: All plants obtained were heterozygous tall. Plants from the F₁ generation were self-pollinated to obtain the F₂ generation.
• F₂ Generation: One homozygous tall plant, two heterozygous tall plants and one homozygous dwarf plant were obtained.

The ratio obtained by crossing for two different traits of a single character is known as monohybrid ratio.

Dihybrid Cross

Mendel carried out the cross breeding by taking two characters together.

Example: Plant with round yellow seeds (RRYY) was crossed with the plant bearing wrinkled green seeds (rryy).

• F₁ Generation: All plants obtained were heterozygous tall. Plants from the F₁ generation were self-pollinated to obtain the F₂ generation.
• F₂ Generation: One homozygous tall plant, two heterozygous tall plants and one homozygous dwarf plant were obtained.
• The phenotypic ratio was 9:3:3:1.

The ratio obtained by breeding two pairs of contrasting characters is called dihybrid ratio.