Saturday, January 29, 2022

DNA: What is a Three-Quarter Sbiling

If the human version is difficult, try using thoroughbreds:
Silver Comic, Comic Strip , Now That's Funny, Red Ransom, and Silver Hawk
Published by: The Courier-Journal (Louisville, KY, 20 Nov 1999, pg 20; newspapers.com.

 a3Genealogy Question Bag 

Question: Are these first cousins as I know them to be? 

Answer: No, it appears you all are three-quarter siblings?  This answer is so much easier to understand in thoroughbred horses!

In the a3Genealogy client's case, one man impregnated three sisters, and married two of them. The third sister married his first cousin. NEVER a dull moment at a3Genealogy and the In-Genes Team. 

What are three quarter siblings? 
The following is a direct copy from the ISOGG WIKI

“Three-quarter siblings are siblings who are genetically half way between full siblings and half siblings. This can happen, for example, if they share the same father but different mothers but their mothers are sisters which makes them effectively both half-siblings and first cousins. An alternative scenario is if a woman has a child with both a man and his father which makes the children related both as half-siblings and half-aunt/uncle vs half-nephew/niece.

Three-quarter siblings can occur as a result of the following scenarios:

·        a man has children with each of two sisters (the children are related as half-siblings and first cousins)

·        a woman has children by each of two brothers (the children are related as half-siblings and first cousins)

·        a woman has children with both a man and his father (the children are related as half-siblings and half-aunt or half-uncle and half-niece or half-nephew)

·        a man has children with both a woman and her daughter (the children are related as half-siblings and half-aunt or half-uncle and half-niece or half-nephew)

Full siblings share on average 50% of their DNA when accounting for both fully identical and half-identical regions. Three-quarter siblings share on average 37.5% of their DNA with both full and half-identical regions.[1] However, the range of sharing for both full siblings and three-quarter siblings is variable. Full siblings can theoretically share between 38% and 61% of their DNA.[2] This means that there can be an overlap in the ranges at the low end of sharing for full siblings and at the high end of sharing for three-quarter siblings.”

Further Research

Continue following the DNA for Genealogists Flipboard Magazine for articles like these. Articles of interest are constantly added. 

Be Historically Correct

Kathleen Brandt

a3genealogy.com
Accurate Accessible Answers
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