Explanation of Range of Genetic Analysis for Genealogical Purposes

The site (www.johnbrobb.com/JBRdna.htm) provides a helpful explanation of the range of genetic analysis used for genealogical purposes. Although it could be briefer, it is in reasonably plain English for the layman.

What I would love to find is a table of dilution by generation for the various factors such as SNPs, STRs, genetic distance (CMs), gene segments etc.

Some of the services including 23andMe and GEDmatch provide data and conclusions but then allow you to infer how they used the one to get the other. As a rule of thumb, it appears that the dilution factor is a ratio of 3:1 for each succeeding generation. You have half your father’s DNA and your child will have 1/4 of your father’s DNA. Also, you have 1/4 of your grandfather’s DNA, as does your cousin, but your cousin will not necessarily inherit the same DNA from your grandfather that you did. However, if you and your cousin are both male and are the children of brothers, then you will both have the same Y-chromosome as do your father, uncle and your grandfather.

The calculation of daughters and X-chromosome and mitochondrial DNA is a different calculus altogether.

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