In general, the walls of arteries are thinner than the walls of veins. true or false?

False.

Artries in general have thicker walls than veins. (thicker tunica media)

This is because artries need to withstand high blood pressure when the heart pumps the oxygenated blood to the rest of the body while veins carry blood (deoxygenated) at lower pressures, hence they are thinner compared to artries

Hope This helps! 

Crossing over creates new combinations of genes in the gametes that are not found in either parent contributing to genetic diversity