Notes on Dihybrid and Monohybrid Crosses

Possible Combinations of Alleles

• Each parent can contribute two alleles for two traits.
• Example: Crossing two plants with the traits of color and height:
  • Parent 1: Green (GG) & Tall (TT)
  • Parent 2: Yellow (yy) & Short (tt)

Allele Contributions

• For the parents mentioned:
  • Parent 1 (purebred) will give offspring dominant alleles,
    e.g., GG TT.
  • Parent 2 (hybrid) can contribute four different combinations due to the mix of alleles.

Dihybrid Cross Explanation

• Dihybrid crosses yield more combinations due to the combination of two traits.
• There are 16 possible combinations of alleles. This is calculated as follows:
  • For one gene (2 alleles):
  • Punnett square: 2 \times 2 = 4 cells.
  • For two genes (4 alleles):
  • Punnett square: 4 \times 4 = 16 cells.

Complexity of Dihybrid Crosses

• As more traits (genes) are introduced, the Punnett square will become more complex.
• Example combinations for dihybrid cross:
  • Possible offspring: [ GG TT, GG Tt, Gg TT, Gg Tt, gg tt, and so on.]

Focus on Monohybrid Cross

• The lesson will start with practicing monohybrid crosses before moving onto dihybrids.
• Monohybrid refers to a single trait being crossed.
• This foundational understanding will aid in learning more complex genetic analysis later on.