Slide 1

Dihybrid CrossesThe Law of Independent AssortmentIndependent AssortmentThe inheritance pattern of one trait will not affect the inheritance pattern of anotherIndependent assortment occurs during meiosisFor a single human gamete, the possible ways chromosomes may assort is astounding:223 = 8,388,608 possible combinationsDihybrid CrossIn 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 ParentsA dwarf pink snapdragon is crossed with a plant homozygous for tallness and red flowers. Dwarf pink = ttRrHomozygous tall, red = TTRRStep #2: Determine Genotypes of GametesA dwarf pink snapdragon is crossed with a plant homozygous for tallness and red flowers. Dwarf pink = ttRrHomozygous tall, red = TTRRtRtrtRtrTRTRTRTR

TRTRTRTRGametes from TALL red parent tRtrtRtrGametes from dwarf pink parentTtRRTtRrTtRrTtRRTtRrTtRRTtRRTtRrTtRrTtRrTtRRTtRRTtRrTtRrTtRRTtRRStep #3: Punnett SquareThe Punnett square determines the genotypes of the offspring

TtRRTtRrTtRrTtRRTtRrTtRRTtRRTtRrTtRrTtRrTtRRTtRRTtRrTtRrTtRRTtRRStep #4: Identify Phenotype Ratios in OffspringTall, red = 8/16Tall, pink = 8/16Tall, white = 0/16Short, red = 0/16Short, pink = 0/16Short, white = 0/16