Questions

Genetic drift or allelic drift is the change in the relative frequency in which a gene variant (allele) occurs in a population due to random sampling and chance.

When is genetic drift a major factor in evolution is

* When there is low gene flow.

* When there is no selective pressure.

* When there is a bottleneck.

Uracil is not found in DNA but found in RNA.

Veins are blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart. In contrast to veins, arteries carry blood away from the heart.

Veins are less muscular than arteries and are often closer to the skin. There are valves in most veins to prevent backflow.