The physical appearance of a trait is called the phenotype of an organism.
C. Organ System
Like said in the definition above, an organ system is a group of organs working together to perform a specific function for the organism.
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Answer:
Natural selection
Explanation:
Natural selection occurs when one allele (or combination of alleles of different genes) makes an organism more or less fit, that it 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.
