How Much DNA Do First Cousins Share? - Genealogy Explained (2024)

FAQs

How Much DNA Do First Cousins Share? - Genealogy Explained? ›

First cousins share an average of 12.5% of their DNA; or 866 centimorgans. The expected range of shared centimorgans is 396-1397, according to the shared centimorgan project. This percentage is the result of genetic recombination that occurs when parents each pass down half of their DNA to their children.

You share around 50% of your DNA with your parents and children, 25% with your grandparents, grandchildren, uncles, aunts, nieces, and nephews, and 12.5% with your first cousins.

The genetic connections between full and half cousins can be quite fascinating. Full cousins share approximately 12.5% of their DNA due to common grandparents, showcasing clear genetic similarities. On the other hand, half-cousins share only 6.25% of their DNA as they share just one grandparent.

At their simplest, these genetic tests look at how much DNA two people share. On average, first cousins share 12.5% of their DNA. An uncle would share more DNA with a niece or nephew, on average about 25%. But first cousins aren't the only ones that share around 12.5% of their DNA.

Someone in this category is likely a brother or sister who shares both biological parents with you. In the rare situation that you have a half sibling who is also your first cousin, they may appear in this category too.

DNA matches who are a first cousin share a match with one of your grandparents. Besides first cousins, the matches in this category can be aunts and uncles, great-aunts and great-uncles, great-nieces and great-nephews, and so forth. These AncestryDNA cousin matches are more distant relatives.

When cousins are in different generations than each other, we say they're removed. "Removed" is like “grand” and “great,” but with cousins. Once removed means a difference of one generation, twice removed means a difference of two generations, and so forth.

An AncestryDNA ^® test can very accurately determine if two people are genetically related at the 3rd or 4th cousin and closer level. This is because AncestryDNA ^® test results are based on the scientific method that identifies people who share long segments of DNA.

Siblings share ~50% of their DNA

But when you inherit these chromosomes from your parents, they get shuffled up a little bit. This is a process called recombination. This mixing up is pretty random. Each time your parents have a child, the DNA will get shuffled up in slightly different ways.

Of these 3 million differences, on average we share about 50 percent of those with our full siblings. Children inherit half of their DNA from their mother and half from their father. However, unless they are identical twins, siblings won't inherit exactly the same DNA.

Can AncestryDNA find half siblings? ›

50 percent of each half sibling's DNA comes from the shared parent, and they inherited about half of the same DNA from that parent as one another. Testing a half sibling can help you fill in that sibling's non-shared parent's ethnicity and show you the ethnicities inherited by that sibling.

Paternity testing is just that: testing for paternity between a possible father and a child. It does not determine whether the man tested is an uncle, brother, grandfather, cousin, etc.

First cousins have an inbreeding coefficient of 0.0625. Anything at or above 0.0156, the coefficient for second cousins, is considered consanguineous; that includes relationships between people and their nephews and nieces.

The majority of babies born to couples who are blood relatives are healthy. Whilst cousin marriage increases the risk of birth defect from 3% to 6%, the absolute risk is still small. Cousin marriage only accounts for a third of birth defects.

Can a half-sibling show up as a cousin? While the amount of DNA you share is different between half-siblings and cousins, your half-sibling still may show up as a “first cousin” because your centimorgans may be within the 1,300 range.

An AncestryDNA ^® test can very accurately determine if two people are genetically related at the 3rd or 4th cousin and closer level. This is because AncestryDNA ^® test results are based on the scientific method that identifies people who share long segments of DNA.

First cousins share an average of 12.5% of their DNA; or 866 centimorgans. The expected range of shared centimorgans is 396-1397, according to the shared centimorgan project. This percentage is the result of genetic recombination that occurs when parents each pass down half of their DNA to their children.

Can a half-sibling show up as a cousin? While the amount of DNA you share is different between half-siblings and cousins, your half-sibling still may show up as a “first cousin” because your centimorgans may be within the 1,300 range.

If you and a relative were to share 17% of your DNA, for example, there would be some probability that the relative is your aunt, your niece, your grandmother, your grandchild, your half sister, or even your first cousin.