How to calculate the percentage DNA that you share with your relatives
Millions of people have had their DNA analyzed. When the results come back you will usually see a list of names, relationships and the approximate percentage shared. An internet search will produce a number of hits on what the percentages should be. I will also again underline why I find the simple fraction “1/2” to possess one of the most important positions in our natural world: see my recent post for other another example.
In this short note I will show some quick examples of where the percentages come from and how you can do the calculations yourself. Here is a helpful link that you will find at “23 and Me” (I am not affiliated in any way). You will likely discover other sources after a quick search.
Figure 1 contains examples for calculating the amounts of DNA that are expected based upon the genetic processes during meiosis and the random fertilization by a random sperm among millions of possibilities.
Have a look at Table 1 and compare the relationships I share with some of my family. The message is this — — you will likely find variation among the theoretical PERCENT EXPECTED and observed (PERCENT SHARED) percentages of shared DNA (see %DIFFERCE) because, as stated above, meiosis and fertilization stem from random processes. I encourage you to note the differences among first, second and first cousins once removed. Refer back to Figure 1 to refresh your memory.
Very few things in biology are ever perfect.
Table 1. Percentage DNA shared among my relatives and me.
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