Which of the following is an example of homoplasy?

a. Hox genes in humans and sea stars
b. streamlined bodies in dolphins and ichthyosaurs
c. astragalus ankle bones in camel and pig
d. hair in humans and fur in bear

The correct answer is option b. "streamlined bodies in dolphins and ichthyosaurs".

Explanation:

An homoplasy is defined as a trait that is shared between two different species but that they do not originate from a common ancestor. An example of homoplasy is the streamlined bodies in dolphins and ichthyosaurs. Ichthyosaurs were reptiles, not mammals like modern dolphins, therefore their similar streamlined bodies evolved separately.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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the answer is a) cell division.

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