Gene S Controls the Sharpness of Spines in a Type

question 53

Multiple Choice

Gene S controls the sharpness of spines in a type of cactus. Cacti with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cacti have dull spines. At the same time, a second gene, N, determines whether or not cacti have spines. Homozygous recessive nn cacti have no spines at all. If cacti heterozygous for both traits, SsNn, were allowed to self-pollinate, the offspring would segregate into which of the following phenotype ratios?

• A) 3 sharp-spined:1 spineless
• B) 1 sharp-spined:2 dull-spined:1 spineless
• C) 1 sharp-spined:1 dull-spined:1 spineless
• D) 9 sharp-spined:3 dull-spined:4 spineless

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Definitions:

Circadian Rhythms

Biological processes that display an endogenous, entrainable oscillation of about 24 hours, regulating various physiological processes including the sleep-wake cycle.

REM Sleep

A stage of sleep characterized by rapid eye movements, low muscle tone, and vivid dreams.

Sleep Onset

The transition from wakefulness into sleep.

Minutes

A written record of the proceedings of a meeting.