Passage I

SLEEPLESS is a fruit fly gene involved in sleep regulation. The normal form of this gene (S+) produces sleep factor protein; a mutant form (S-) does not produce the protein.

Researchers studied the sleep patterns and survival of flies of the same age that had the genotype S+S+, S+S- or S-S- . Figure 1 shows the amount of sleep, and the number of sleep events, per day per fly for each genotype. Figure 2 shows the amount of recovery sleep (additional sleep needed following 6 hr of sleep deprivation) per day per fly for each genotype. Figure 3 shows how percent survival varied with age for each genotype.

Figures adapted from Kyunghee Koh et al., "Identification of SLEEPLESS, a Sleep-Promoting Factor." ©2008 by the American Association for the Advancement of Science.

5. Suppose that a fly with the genotype S+S+ is crossed with a fly with the genotype S-S- resulting in 80 offspring. Based on Figure 3, the number of these offspring still alive at 50 days of age will most likely be closest to which of the following?

Answer and Explanation

Your Answer is

Correct Answer is C

Explanation

First, the genotype of the first generation of offspring mated with genotype S+S+ and SS- is S+S-;

Then according to the S+S-curve of figure 2, it can be seen that when the abscissa When it is 50 days, the ordinate percent survial is about 75%;

The total number of offspring given in the question stem is 80, so the number of surviving individuals is 80×75%=60