Single-Trait Inheritance Review

1. Single-Trait Inheritance Review • Since one allele is inherited from each parent, various genotypes are possible • The dominant phenotypes is expressed if the offspring is either heterozygous or homozygous for the dominant allele • The recessive phenotype is expressed only if the offspring is homozygous for the recessive allele

2. Recall • Cross between a pea plant homozygous for round seeds and a pea plant that has wrinkled seeds 100% phenotype are round and 100% genotype are Rr • Cross between a pea plant heterozygous for round seeds and a pea plant that has wrinkled seeds ½ phenotypes are round and ½ wrinkled ½ genotypes Rf and ½ rr • Cross between two pea plants heterozygous for round seeds ¾ phenotypes are round and ¼ wrinkled ¼ genotype RR, ½ genotype Rr and ¼ rr

3. Dihybrid Cross

4. Mendel • Studied the inheritance of two separate traits in crossbreeding 1

5. By doing other crosses, Mendel soon discovered that alleles assort independently • Law of independent assortment: If genes are located on separate chromosomes; they are inherited independently of each other

6. Probability • number a ways that a given event could occur total number of possible events • Chance has no memory • Chance of tossing heads once is ½, the possibility of tossing heads twice is ½ x ½ = ¼

7. Sample Problem Green seeds (G) are dominant to yellow seeds (g) and smooth seeds (R) are dominant to wrinkled seeds (r) A heterozygous green and heterozygous smooth seeded plant is crossed with a homozygous green and wrinkled seed plant GgRr x GGrr

8. When doing the cross, you must first determine the possible gametes from each parent (notice each gamete has 1 allele from each pair) • GgRr  possible gametes are: GR, Gr, gR, gr • GGrr  possible gametes are: Gr, Gr, Gr, Gr

9. Recall Parents: GgRr x GGrr Gametes: Gr, Gr, Gr, Gr and GR, Gr, gR, gr • When doing a dihybrid cross, use a 4 x 4 Punnett square GR Gr gR gr Notice that the genotypes in this row repeat in the next 3 rows… Gr Gr Gr Gr

10. Parents:GgRr x GGrr • Luckily there is a shortcut if any gametes of a parent are duplicated GgRr – GR, Gr, gR, gr GGrr – Gr, Gr, Gr, Gr  only possible gamete is Gr GR Gr gR gr Gr • This revised Punnett is all you would need to write but you need to remember that the removed offspring still count • For example, if I asked how many offspring had the genotype GGRr, you would need to write 4

11. Work • Finish hand-out

12. Thanks to Kelly.