1. Exploring Mendelian Genetics

2. Independent Assortment Does the segregation of one pair of alleles affect the segregation of another pair of alleles? –Mendel performed an experiment to follow two different genes from generation to generation in a Two-Factor Cross = Dihybrid Cross

3. Two-Factor Cross: F1 Generation Mendel crossed true-breeding plants that produced only round yellow peas (RRYY) with plants that produced wrinkled green peas (rryy). All F1 offspring from this cross had round yellow peas (RrYy) This cross produced hybrid plants for the next cross…

4. Dihybrid Cross Cross a Round, Yellow peas plant (RRYY) with plants that produce Wrinkled, Green peas (rryy). RRYY x rryy R = round seed r = wrinkled seed Y = yellow seed y = green seed RY ry RrYy All offspring produced have Round, Yellow peas. Round, Yellow

5. Two-Factor Cross: F2 Generation –Mendel crossed two F1 plants (RrYy) heterozygous for both seed shape and color –Using a Punnett square, we can see that alleles for seed shape segregate independently of those for seed color = independent assortment.

6. Dihybrid Cross Cross two plants that are heterozygous for round, yellow seeds (RrYy). RrYy x RrYy R = round seed r = wrinkled seed Y = yellow seed y = green seed RYRyrYry RY Ry rY ry RRYY RRYyRrYYRrYy RRYyRRyyRrYy Rryy RrYY RrYyrrYY rrYy RrYy RryyrrYyrryy Phenotype Ratio - Round, Yellow Round, Green Round, Yellow Round, Green Wrinkled, Yellow Wrinkled, Green 9 Round, Yellow 3 Round, Green 3 Wrinkled, Yellow 1 Wrinkled, Green 9 : 3 : 3 : 1 Ratio

7. Dihybrid Cross Genotype Ratio – 1 RRYY :2 RRYy : 2 RrYY : ….Ahhh! Punnett square shows a 9:3:3:1 phenotypic ratio – 9 yellow round : 3 yellow wrinkled : 3 green round: 1 green wrinkled

8. Principle of Independent Assortment Genes for different traits can segregate independently during the formation of gametes.

9. Summary of Mendel’s Principles –Inheritance of biological information is determined by genes –Some forms of a gene may be dominant or recessive –Each adult organism has two copies of each gene – one from each parent –Alleles for different genes usually segregate independently of one another