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Dihybrid Crosses The Law of Independent Assortment.

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Presentation on theme: "Dihybrid Crosses The Law of Independent Assortment."— Presentation transcript:

1 Dihybrid Crosses The Law of Independent Assortment

2 Independent Assortment The inheritance pattern of one trait will not affect the inheritance pattern of another Independent assortment occurs during meiosis For a single human gamete, the possible ways chromosomes may assort is astounding: 2 23 = 8,388,608 possible combinations

3 Dihybrid Cross In snapdragons, tallness (T) is dominant to dwarfness(t), while red color is due to gene (R) and white to its corresponding allele (r). The heterozygous condition results in pink (Rr) flower color. A dwarf pink snapdragon is crossed with a plant homozygous for tallness and red flowers. Give the possible genotypes and corresponding phenotypes for all of the possible F 1 generation.

4 Step #1: Determine Genotypes of Parents A dwarf pink snapdragon is crossed with a plant homozygous for tallness and red flowers. Dwarf pink = ttRr Homozygous tall, red = TTRR

5 Step #2: Determine Genotypes of Gametes A dwarf pink snapdragon is crossed with a plant homozygous for tallness and red flowers. Dwarf pink = ttRr Homozygous tall, red = TTRR tRtrtR tr TR

6 Gametes from TALL red parent tR tr tR tr pink Gametes from dwarf pink parent TtRR TtRr TtRR TtRr TtRR TtRr TtRR TtRr TtRR Step #3: Punnett Square The Punnett square determines the genotypes of the offspring

7 TtRR TtRr TtRR TtRr TtRR TtRr TtRR TtRr TtRR Step #4: Identify Phenotype Ratios in Offspring Tall, red = 8/16 Tall, pink = 8/16 Tall, white = 0/16 Short, red = 0/16 Short, pink = 0/16 Short, white = 0/16


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