If the mean of a phenotypic characteristic in a population changes over time but the distribution remains the same, then we say that the population has undergone selection.

Directional selection

Explanation:

In population genetics, directional selection is a mode of natural selection in which the mean of a phenotypic characteristic in a population changes over time but the distribution remains constant.

Directional selection occurs mostly under environmental changes and when populations migrate to new areas with different environmental pressures.

many phylogenetic trees have a single lineage at the base representing a common ancestor. a lineage that evolved early from the root and remains unbranched is called basal taxon. when two lineages stem from the same branch point, they are called sister taxa.

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explanation:

there are 35 white marbles

step-by-step explanation:

y- yellow marbles

4y + 5 = 45

subtract 5 from both sides

4y = 40

divide for from both sides

y = 10

plug in 10 to get 40 yellow marbles then subtract by 5 to get 35 marbles

thus there are only 10 yellow marbles