Answer: Natural selection occurs when one allele (or combination of alleles of different genes) makes an organism more or less fit, that is, able to survive and reproduce in a given environment. If an allele reduces fitness, its frequency will tend to drop from one generation to the next.
Explanation:
25.A
26.C
27.A
28.C
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The right answer is All answer options describe plasmids.
A plasmid is a natural or artificially modified circular DNA molecule for use in biological research.
The researchers use the plasmids to insert a DNA fragment of interest, thanks to the cloning cassettes. They can clone genes to express proteins or RNAs and analyze them.