What is a mutation? why are mutations more serious when they occur in a sex cell?

A mutation occurs when a DNA gene is damaged or changed in such a way as to alter the genetic message carried by that gene.

Mutation in sex cells are more serious because they are heritable and affect the next generation.

imagine a line passing through the center of earth that goes through both the north pole and the south pole. this imaginary line is called an axis. earth spins around its axis, just as a top spins around its spindle. this spinning movement is called earth's rotation. at the same time that the earth spins on its axis, it also orbits, or revolves around the sun. this movement is called revolution.