Use the Following Information to Answer the Question What Is the Greatest Benefit of Having Used a Testcross

question 55

Multiple Choice

Use the following information to answer the question.
A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine.
A geneticist performed a testcross with an organism that had been found to be heterozygous for the three recessive traits, and she was able to identify progeny of the following phenotypic distribution (+ = wild type) :
$$\begin{array} { | l | l | l | l | l | } \hline \text { Phenotypes } & \text { Leaves } & \text { Stems } & { \text { Roots } } & { \text { Number } } \\\hline1 & a & + & + & 14 \\\hline 2 & a & + & c & 0 \\\hline 3 & a & b & + & 32 \\\hline 4 & a & b & c & 440 \\\hline 5 & + & b & + & 0 \\\hline 6 & + & b & c & 16 \\\hline 7 & + & + & c & 28 \\\hline 8 & + & + & + & 470 \\\hline &&& \text { Total } & 1000 \\\hline\end{array}$$
What is the greatest benefit of having used a testcross for this experiment?

• A) The homozygous recessive parents are obvious to the naked eye.
• B) The homozygous parents are the only ones whose crossovers make a difference.
• C) The phenotypes of the progeny reveal the allelic content of the gamete from the heterozygous parent.
• D) All of the progeny will be heterozygous.

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