In Drosophila, Singed Bristles (Sn)and Carnation Eyes (Car)are Both Caused

question 17

Multiple Choice

In Drosophila, singed bristles (sn) and carnation eyes (car) are both caused by recessive X-linked alleles.The wild-type alleles (sn⁺ and car⁺) are responsible for straight bristles and red eyes, respectively.A sn car female is mated to a sn⁺ car⁺ male and the F₁ progeny are interbred.The F₂ are distributed as follows:
$$\begin{array} { | l | r | } \hline s n~ c a r & 55 \\\hline s n~ c a r^+ & 45\\\hline s n ^{+ c a r} & 45 \\\hline s n ^ { + c a r +} & \underline{55} \\\hline & 200 \\\hline\end{array}$$
-If you want to analyze this data for evidence of linkage between sn and car, what is the null hypothesis?

• A)Genes sn and car are linked.
• B)Genes sn and car are not linked.
• C)Genes sn and car are located close together on the same chromosome.
• D)Crossing-over sometimes occurs between sn and car.

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