NOTES – Genetics: Independent Assortment & Dihybrid Crosses

1. NOTES – Genetics: Independent Assortment & Dihybrid Crosses

2. Are traits inherited together? • Mendel wondered if the inheritance of one trait had anything to do with the inheritance of another • Dihybrid Cross (Two-Factor Cross) – a cross where two traits are examined at the same time • (EX. Tongue Rolling & PTC Tasting)

3. What did Mendel do? • Mendel looked at seed shape and seed color • Shape: R = round r = wrinkled • Color: Y = yellow y = green • P1 = true-breeding round, yellow seed plant with true breeding wrinkled, green seed plant • P1 = RRYY x rryy

4. The F1 Generation

5. The F1 Generation • Each true-breeding round, yellow seed plant produces gametes with one round allele and one yellow allele (RY) • Each true-breeding wrinkled, green seed plant produces gametes with one wrinkled allele and one green allele (ry) • 100% of the offspring are heterozygous for both traits (RrYy) and produce round yellow seeds

6. The F2 Generation • When the F1 generation is allowed to cross-pollinate (RrYy X RrYy), would round and yellow stay together or would they separate? What about wrinkled and green? • When Mendel crossed his F1 plants, he got round, yellow seed plants and green, wrinkled seed plants but he also got round, green seed plants and wrinkled, yellow seed plants

7. The F2 Generation

8. Each heterozygous round, yellow seed plant can produce four different allele combinations in its gametes (RY, Ry, rY, ry) The phenotypic ratio of the offspring was 9:3:3:1 Conclusion: The inheritance of one trait does not influence the inheritance of another The F2 Generation

9. The Principle of Independent Assortment • Genes for different traits are inherited independently from one another • EX. During pea plant gamete formation, the gene that determines seed color assorts independently from the gene that determines seed shape • You can get round with yellow OR round with green OR wrinkled with yellow OR wrinkled with green