Trihybrid crosses

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Trihybrid crosses

  1. 1. Trihybrid cross BAKHTIARI_HOSSEIN Figure 3-2 Copyright © 2006 Pearson Prentice Hall, Inc.
  2. 2. Trihybrid crossThe mating of two individuals, organisms, or strains that have different gene pairs that determine three specific traits or in which three particular characteristics or gene loci are being followed.
  3. 3. Example:23 = 8 * 8 = 64MEANING:The fork line method can be used by figuring the occurrence of each gene or set of genes to be found in the gamete, and then multiply them together. This can be multiplied by figuring each trait or combination of traits separate for both the male and female, or each gene individually regardless of sex.
  4. 4. P1: WWGG * ww ggF1: Ww Gg * Ww GgF2: Ww * Ww Gg * Gg WW Ww Ww ww GG Gg Gg ggPhenotypes: ¾W ¾ G = 9/16 WG ¼ g = 3/16 Wg ¼ w ¾ G = 3/16 wG ¼ g = 1/16 wgPhenotypic ratio: 9:3:3:1
  5. 5. Genotypes: ¼ GG = 1/16 WW GG ¼ WW 2/ 4 Gg = 2/16 WW Gg ¼ gg = 1/16 WW gg ¼ GG = 3/16 Ww GG 2/4 Ww 2 /4 Gg = 4/16 Ww Gg ¼ g = 2/16 Ww gg ¼ GG = 1/16 ww GG ¼ ww 2 /4 Gg = 2/16 ww Gg ¼ gg = 1/16 ww gggenotypic ratio: 1:2:1:2:4:2:1:2:1
  6. 6. Trihybrid Crosses• Trihybrid or three-factor cross• More complex by “easily” calculated following principles of segregation, independent assortment and probability• Punnett square has 64 boxes…• Demonstrates that Mendel’s principles apply to inheritance of multiple traits
  7. 7. .
  8. 8. Forked-line Method• Also called branch diagram

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