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Dihybrid Cross

Dihybrid Cross. A dihybrid is an individual that is heterozygous ( Tt ) for TWO traits

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Dihybrid Cross

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  1. Dihybrid Cross • A dihybrid is an individual that is heterozygous (Tt) for TWO traits • Brown hair (B) is dominant over blonde hair (b) and green eyes (G) is dominant over blue eyes (g), then the genotype of an individual that is heterozygous (hybrid) for BOTH traits (dihybrid) would be “BbGg”. BbGg (mom) X BbGg (dad)

  2. Dihybrid Cross • In order to do a cross between the dihybrids, you must first determine what combination of alleles can be in the gametes. B b G g(mom) X B b G g(dad) First = ____ Outer = ____ Inner = ____ Last = ____ First = ____ Outer = ____ Inner = ____ Last = ____

  3. Dihybrid Cross • In order to do a cross between the dihybrids, you must first determine what combination of alleles can be in the gametes(eggs & sperm) B b G g(mom) X B b G g(dad) bg bG BG Bg First = Outer = Inner = Last = First = Outer = Inner = Last = Bg BG bg bG

  4. Dihybrid Cross *Important: You can only have ONE allele for each trait in each gamete. So, you can only have ONE “B” and ONE “G” in each gamete. Since both parents have the same genotype (BbGg), the alleles in their gametes will be the same for both. Once you have determined what the different combinations of alleles is, put them on the Punnett square.

  5. B G B g b G b g B G B g b G bg

  6. BB GG BB Gg Bb Gg BB GG B G B g b G b g B G BB gg Bb Gg Bb gg BB Gg B g Bb GG Bb Gg bb Gg bb GG b G bg Bb gg bb gg Bb Gg bb Gg

  7. Possible Phenotypes# of Individuals Brown hair (dom) & Green eyes (dom) = __ Brown hair (dom) & Blue eyes (rec) = __ Blonde hair (rec) & Green eyes (dom) = __ Blonde hair (rec) & Blue eyes (rec) = __

  8. Possible Phenotypes# of Individuals Brown hair (dom) & Green eyes (dom) = _ Brown hair (dom) & Blue eyes (rec) = __ Blonde hair (rec) & Green eyes (dom) = __ Blonde hair (rec) & Blue eyes (rec) = __ 9

  9. Possible Phenotypes# of Individuals Brown hair (dom) & Green eyes (dom) = _ Brown hair (dom) & Blue eyes (rec) = __ Blonde hair (rec) & Green eyes (dom) = __ Blonde hair (rec) & Blue eyes (rec) = __ 9 3

  10. Possible Phenotypes# of Individuals Brown hair (dom) & Green eyes (dom) = _ Brown hair (dom) & Blue eyes (rec) = __ Blonde hair (rec) & Green eyes (dom) = __ Blonde hair (rec) & Blue eyes (rec) = __ 9 3 3

  11. Possible Phenotypes# of Individuals Brown hair (dom) & Green eyes (dom) = _ Brown hair (dom) & Blue eyes (rec) = __ Blonde hair (rec) & Green eyes (dom) = __ Blonde hair (rec) & Blue eyes (rec) = __ 9 3 3 1

  12. Bottom line is…..any time you do a cross between two organisms that are dihybrids…no matter what the traits are, the phenotypic ration will ALWAYS be 9 : 3 : 3 :_1_

  13. B G B g b G b g BB GG BB Gg Bb GG Bb Gg B G Bb gg Bb Gg BB Gg BB gg B g b G Bb GG bb Gg bb GG Bb Gg bg Bb Gg Bb gg bb gg bb Gg

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