Why do veins also have valves? to keep the blood from circulating too fast
to regulate contractions of the heart
to keep the veins from losing blood
to prevent gravity from pulling the blood towards the feet

(middle school btw)

Neeed now for 1. eye color is a polygenic trait. what is the possibility of getting a green (aabb) eyed child, if parent 1 has brown eyes (aabb) parent 2 has blue eyes (aabb) 2.albinism is a recessive trait. having normal pigment is the dominant trait. what is the possibility of having an albino child if parent 1 is heterozygous normal parent 2 is heterozygous normal 3.in rabbits black fur is dominant over white fur. what is the probability of getting a rabbit with black fur if parent 1 is heterozygous black parent 2 is homozygous white