The key distinction is that in genetic drift allele frequencies change by chance, whereas in natural selection allele frequencies change by differential reproductive success. If the frequencies of traits in a population change purely by chance , then genetic drift has occurred.
A blockage of the left subclavian artery would interfere with blood flow to the left arm.
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A species must have an appropriate food source, not have too many predators feeding on them, and have a suitable climate for which the species is adapted to.
Chromatin is a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells. Chromatin exists in two forms. ... One form, called euchromatin, is less condensed and can be transcribed.