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Dihybrid test cross or back cross

Dihybrid test cross or back cross. Dihybrid test cross/back cross. As in monohybrid crosses, you can’t tell by looking at the dominant trait whether it is homozygous or heterozygous. Dihybrid test cross/back cross.

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Dihybrid test cross or back cross

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  1. Dihybrid test cross or back cross

  2. Dihybrid test cross/back cross • As in monohybrid crosses, you can’t tell by looking at the dominant trait whether it is homozygous or heterozygous.

  3. Dihybrid test cross/back cross • As in monohybrid crosses, you can’t tell by looking at the dominant trait whether it is homozygous or heterozygous. • So in order to find out what the genotype is – do a test cross with an organism that has both recessive characteristics.

  4. Dihybrid test cross/back cross • As in monohybrid crosses, you can’t tell by looking at the dominant trait whether it is homozygous or heterozygous. • So in order to find out what the genotype is – do a test cross with an organism that has both recessive characteristics. • If the parent is heterozygous you get a ratio of 1:1:1:1

  5. Dihybrid test cross/back cross • As in monohybrid crosses, you can’t tell by looking at the dominant trait whether it is homozygous or heterozygous. • So in order to find out what the genotype is – do a test cross with an organism that has both recessive characteristics. • If the parent is heterozygous you get a ratio of 1:1:1:1 • If it is homozygous, all the offspring will show the dominant phenotype for both characteristics.

  6. Example Genotype: AaBb x aabb Gametes:

  7. Example Genotype: AaBb x aabb Gametes: AB AbaBabab

  8. Example Genotype: AaBb x aabb Gametes: AB AbaBabab Punnett Square:

  9. Example Genotype: AaBb x aabb Gametes: AB AbaBabab Punnett Square:

  10. Example • Now, you have an organism that is homozygous dominant for one trait, but heterozygous for the other – the test cross/back cross still works.

  11. Example • Now, you have an organism that is homozygous dominant for one trait, but heterozygous for the other – the test cross/back cross still works. • In the cross: • For the homozygous dominant characteristic, no recessive trait will show up in the offspring

  12. Example • Now, you have an organism that is homozygous dominant for one trait, but heterozygous for the other – the test cross/back cross still works. • In the cross: • For the homozygous dominant characteristic, no recessive trait will show up in the offspring • For the heterozygous characteristic the recessive trait will show up

  13. Example Genotype: AABb x aabb Gametes:

  14. Example Genotype: AABb x aabb Gametes: AB ABAbAbabababab

  15. Example Genotype: AABb x aabb Gametes: AB ABAbAbabababab PunnettSq:

  16. Example Genotype: AABb x aabb Gametes: AB ABAbAbabababab PunnettSq:

  17. Example Genotype: AABb x aabb Gametes: AB ABAbAbabababab PunnettSq: • ALL show the dominant trait for A and HALF show the recessive trait for B. From this, you can deduce the genotype as AA for trait A and Bb for trait B

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