Mendel’s experiment with Round, yellow and green, wrinkled seeds
YYRR x yyrr. Egg: YR. Sperm: yr. When you cross this, you get all YyRr for the PARENTS. Mendel thought that these genes would move together. This would give a ratio of 3:1 if it was true.
ratio of 9:3:3:1
use FOIL to find out all possible combinations of genes. First would be YR, Yr, rY, and yr on both sides. This is f1 generation after you cross YyRr with each other.
Principle of independent assortment
Each pair of alleles separates independently (without regard to how the
others separate).
All possible combinations of factors can occur in the gametes in roughly
equal proportions.
This occurs when genes are found on separate chromsomes or very far
apart on the same chromosome.
Two gene test cross
- can be used to test whether an F2 individual showing both dominant traits is homozygous for one or both of the genes
- can also be used to test for independent assortment. Since the F1 generation of a known dihybrid cross should yield only double heterozygotes, any test cross of an F1 should always yield a 1:1:1:1 ratio under Mendelian rules. Any deviation from that ratio may be due to failure of alleles to sort independently (linkage).
if one unknown allele is dominant….
If one unknown allele is dominant and one recessive, the two gene test cross will yield a 1:1 ratio, with only two phenotypes. (Note a dominant R and recessive y would yield a ratio of 1 round yellow : 1 round green.)
If both unknowns are recessive,
the two gene test cross will yield equal numbers of four different phenotypes (1:1:1:1).
Dihybrid cross
when you cross YyRr with YyRr. Phenotypic ratio is 9:3:3:1
