There are three sources of genetic variation: mutation, gene flow, and sexual reproduction. A mutation is simply a change in the DNA.
For the first question, I believe it's 36. For the second question, it is oxygen, as oxygen is essential for aerobic processes. For the last question, the summarized cellular respiration equation is the 2nd one.
Directional selection acts against b<span>oth extremes simultaneously in the variation of the trait. This is the most "aggressive" form of selection and only happens in extreme areas.
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