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    Dihybrid test cross

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    Consider the following two genotypes: AABB , aabb where A and B are dominant and a and b are recessive:

    1) What is the genotype of the F1 progeny from an AABB x aabb cross?

    2) Construct a Punnet square of the F1 self cross (i.e. F1 x F1). What are the genotypic ratios from this testcross? What are the phenotypic ratios?

    3) Construct a Punnet square of the F1 genotype with the AABB parental. What are the genotypic ratios from thsi cross? What are the phenotypic ratios?

    4) Construct a Punnet square of the F1 genotype with the aabb parental. What are the genotypic ratios? What are the phenotypic ratios?

    5) If you had an organism that was A- B- and wanted to determine its exact genotype, which cross would you use? Explain your answer.

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    Solution Preview

    1) What is the genotype of the F1 progeny from an AABB x aabb cross?
    First, determine the gametes possible for each parent. AABB can only produce AB gametes. aabb can only produce gametes aa. The only possible offspring are AaBb

    2) Construct a Punnet square of the F1 self cross (i.e. F1 x F1). What are the genotypic ratios from this testcross? What are the phenotypic ratios?
    Since all the offspring on the cross are AaBb, the F1 cross would be AaBb x AaBb

    Punnett square

    AB Ab aB ab
    AB AABB AABb AaBB ...

    Solution Summary

    Detailed explanation of dihybrid test crosses with Punnett squares.

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