The Law of Independent Assortment Dihybrid Crosses The Law of Independent Assortment

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: 223 = 8,388,608 possible combinations

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 F1 generation.

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

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

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