Hairy ears are inherited as a Y-linked trait. A man with hairy ears has a daughter who has a son with a man who does not have hairy ears. What is the probability that the hairy-eared man's grandson has hairy ears?

zero

Explanation:

Y-linked traits do not occur in females as they do not possess the Y chromosome, and occur in all male descendants of an affected male. Since the affected grandfather produces  daughter. She is unaffected and then mates with an unaffected male that does not have hairy hairs. The son produced between them will not have hairy hairs.

If the grandfather had sired a son, his son will be affected and then the son can pass on this trait to his own son.

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what statement best describes the difference between the sympathetic and parasympathetic nervous systems?

the sympathetic nervous system prepares the body for intense physical activity and is often referred to as the fight-or-flight response. the parasympathetic nervous system has almost the exact opposite effect and relaxes the body and inhibits or slows many high energy functions.