Variations Produced by Meiosis
Fertilization involves the union of a male (sperm) and female (egg) gamete, and its product is called a zygote. This process produces random combinations of genetically diverse sperm and eggs, which allows unlimited outcomes for variation. Fertilization is what makes every human being genetically different.
Nondisjunction is when chromosomes within the cell don't separate the way they're supposed to, causing both chromosomes to go to a single daughter cell. This mistake in the meiotic process is responsible for extra and/or missing chromosomes that may lead to birth defects or miscarriages.