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Meiosis & Mitosis

Meiosis is one of the two processes of cell replication. This one focused on creating the Gamete or sex cells (sperm and egg) that contain 1/2 the chromosomes of the original cell. Or the haploid cells as they are sometimes called.  

Mitosis is the other cell replication process. It is different than Meiosis in that it is creating a complete diploid copy of the original cell. It occurs all the time by replacing dying and old cells.  

Both processes start with the process of DNA Replication to create a copy of all the chromosomes — a copy of each strand of each type of chromosome.  The difference is Mitosis then creates two cells that are identical to the original. Each containing two copies of each autosome.  Meiosis creates 4 cells that each only contain one of each strand of the original chromosome pairs and one somal sex chromosome. That is, haploid cells. Mitosis retains the original cells two somal chromosomes.

You really do not need to understand this difference for genetic genealogy,  Except that it is during the Meiosis process that recombination occurs. As well as a detectable change in a copy that eventually leads to off-spring carrying that change. Once a gamete is created, it is not further replicated. Simply being used for sexual reproduction. So there are likely gametes in each of you that have different, detectable changes that can be passed down. This is key to understanding how one sibling can have a unique change that other siblings and the parents do not share.

The only non-nuclear, non-chromosome DNA is the Mitochondria located in the cell body.  This has a different process for replication and is passed in-tact down to the new cells in both cell division processes.