Chromosomes+and+Genetic+Variability+By+Karen,+Jess+and+Kat

Meiosis summary
When we begin life at conception, we have 46 chromosomes as we develop, the cells split and each of the created cells contains 46 chromosomes. During //mitosis//, chromosomes duplicate themselves exactly. Cells go through this duplication process regularly, for example, cancer cells duplicate faster than healthy cells.

The process of //meiosis// transfers genetic information between generations. It occurs when sperm and ova are being formed. The cells divide once, like in mitosis, but they then duplicate again forming four cells each containing 23 chromosomes. At conception, sperm is only 1-5 days old, but the ova were formed during female conception, so they are the age of the female, plus a few months. This is why age is crucial when trying to conceive if you are female, because the ova are so much older than the sperm.

Meiosis gives two guarantees for inherited variability (sexual reproduction depends on inherited variability):


 * 1) Chromosomes in the germ cells are shuffled, so they are no longer simply ordered 1-23. This happens again during second division. With 23 pairs, the possibility for random selection is about 8 million, which represents the number of possible chromosome arrangments.
 * 2) Crossing over takes place during meiosis before the first cell division through the exchange of genetic material.