Discussion
An individual has four heterozygous loci. What will be the total number of different genotypes produced in \(\text{F}_{2}\) ?
Answer: C
The F2 has 81 different genotypes.
Each heterozygous locus (Aa) segregates into three genotypes in the F2: AA, Aa and aa. Loci assort independently, so the counts multiply:
\[ \begin{aligned} \text{genotypes} &= 3^{n} \\ &= 3^{4} = 81 \end{aligned} \]
The distractors come from the other standard formulas: \(2^{4} = 16\) is the number of gamete types and of phenotypes with complete dominance, \(4^{4}\) gives the number of gamete combinations, and \(3^{3} = 27\) would apply to only three loci. 64 is \(4^{3}\), which fits none of these.
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