Question

which of the following best describes directional selection?

when a favoured trait is at one end of a spectrum.

when a favoured trait progress the organism in a beneficial direction

when the favoured trait involves physical increases in organism size.

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Explanation:

Directional selection is a type of natural selection where the environmental pressures favor one extreme phenotype (trait) over others, shifting the population's trait distribution toward that one end of the trait spectrum. The option "When a favoured trait is at one end of a spectrum" aligns with this definition. The second option's wording ("progress the organism in a beneficial direction") is vague and not the standard definition, and the third option is incorrect as directional selection isn't limited to physical size increases.

Answer:

A. When a favoured trait is at one end of a spectrum.