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Consider the cross AaBbCCDd x aaBBccDd. If the genes are independently assorting, how many different genotypes are possible in the offspring?

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8
16
24
32
none of these choices

1 Answer

5 votes

Final answer:

The cross AaBbCCDd x aaBBccDd can produce 4 different genotypes because there is only one possibility at the B and C loci and two possibilities at the A and D loci. The number of possible genotypes is not among the listed choices in the question.

Step-by-step explanation:

To determine how many different genotypes are possible in the offspring from the cross AaBbCCDd x aaBBccDd, we need to consider each gene locus independently because the genes are independently assorting according to Mendel's law of independent assortment. For each locus (gene), the possible genotypes come from the combination of alleles from each parent.

At the first locus (A/a), the possible genotypes for the offspring are Aa and aa since one parent is Aa and the other is aa. At the second locus (B/b), the offspring can only have the genotype Bb because one parent is Bb and the other is BB. For the third locus (C/c), the offspring can only be Cc since one parent is CC and the other is cc. Finally, at the D/d locus, the possible genotypes are Dd and dd because both parents are Dd.

We can now calculate the total number of genotypes by multiplying the number of genotypic possibilities at each locus:
2 (from A/a) x 1 (from B/b) x 1 (from C/c) x 2 (from D/d) = 4 different genotypes.

However, we have to bear in mind that the A/a and D/d loci will each produce heterozygotes that can be represented in two different ways (e.g., Aa and aA, Dd and dD), even though they represent the same genotype. Therefore, the corrected calculation would avoid this double counting, which actually gives us:

2 (A or a) x 1 (B only) x 1 (C only) x 2 (D or d) = 4 genotypes.

Since we do not multiply by more than one for the B and C loci as they can only produce one type of gamete at each locus, the total number of different genotypes that can be produced in the offspring is 4. Therefore, the correct answer is not among the provided choices.

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