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.

the dna molecules have a negative charge because of the phosphate groups in their sugar-phosphate backbone, so they start moving through the matrix of the gel towards the positive pole. power is turned on and dna fragments migrate through gel (towards the positive electrode).

explanation: