A testcross of trihybrid Drosophila produced the following phenotypes and number of offspring. A table showing phenotype and the number of offspring with each phenotype is below. A plus sign is used for wild-type phenotype; a letter indicates the mutant phenotype for that gene. $\begin{array} { l r } + + + & 669 \\a b c & 653 \\+ + c & 121 \\a b + & 139 \\+ b + & 2280 \\a + c & 2215 \\+ b c & 3 \\a + + & 2\end{array}$
-The cross represented by a^+b+c+/abc × abc/abc is

Question

A testcross of trihybrid Drosophila produced the following phenotypes and number of offspring. A table showing phenotype and the number of offspring with each phenotype is below. A plus sign is used for wild-type phenotype; a letter indicates the mutant phenotype for that gene.

\begin{array} { l r } + + + & 669 \\a b c & 653 \\+ + c & 121 \\a b + & 139 \\+ b + & 2280 \\a + c & 2215 \\+ b c & 3 \\a + + & 2\end{array}

-The cross represented by a^+b+c+/abc × abc/abc is

Quizplus · Accepted Answer

This is a three-point testcross because it involves three genes (a, b, and c) and their respective alleles being crossed. The presence of three different phenotypes (a, b, c) and their combinations in the offspring indicates that three loci are being analyzed for their genetic linkage and recombination frequencies.

A Testcross of Trihybrid Drosophila Produced the Following Phenotypes and Number