Presentation on theme: "The Law of Independent Assortment"— Presentation transcript:
1 The Law of Independent Assortment Dihybrid CrossesThe Law of Independent Assortment
2 Independent Assortment The 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 combinations
3 Dihybrid 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.
4 Step #1: Determine Genotypes of Parents “A dwarf pink snapdragon is crossed with a plant homozygous for tallness and red flowers. “Dwarf pink = ttRrHomozygous 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 = ttRrtRtrtRtrHomozygous tall, red = TTRRTRTRTRTR
6 Gametes from TALL red parent Step #3: Punnett SquareThe Punnett square determines the genotypes of the offspringGametes from TALL red parentTRTRTRTRtRTtRRTtRRTtRRTtRRtrTtRrTtRrTtRrTtRrGametes from dwarf pink parenttRTtRRTtRRTtRRTtRRtrTtRrTtRrTtRrTtRr
7 Step #4: Identify Phenotype Ratios in Offspring Tall, red = 8/16Tall, pink = 8/16Tall, white = 0/16Short, red = 0/16Short, pink = 0/16Short, white = 0/16TtRRTtRRTtRRTtRRTtRrTtRrTtRrTtRrTtRRTtRRTtRRTtRRTtRrTtRrTtRrTtRr