Do Half Cousins Share Any DNA? How Much?

If you’ve been doing genealogical research for a lengthy period of time, the term “half-cousin” is virtually guaranteed to have come up. But what does half-cousin actually mean? Read on to learn how exactly half-cousins share DNA, and what half-first, half-second, and half-third cousins are.

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Half-cousins, as you might assume, typically have about half of the normal amount of shared DNA between cousins.

Each of us has at least one half-first, half-second, half-third, half-fourth, half-fifth, and half-sixth cousin. Numerous family conditions may result in cousins having “half” kinship.

What Is A Half Cousin And How Much DNA Do We Share?

If you received an autosomal DNA test, it is critical to understand your half-cousins. Half-relatives generally share around half the DNA of “full” cousins.

It is important to stress that being “half cousins” does not always influence how two cousins feel about one another or how they negotiate their own familial relationships. However, it is a helpful phrase for genealogists (and certain scientists) to indicate which relatives have common ancestors.

Due to the fact that you may not share DNA with any cousin more distant than your third cousin—regardless of whether they are half- or full-cousins—standard ranges of shared DNA aren’t as important in more distant connections.

The closer the two cousins, the more straightforward it is to look at the amount of shared DNA between them to determine whether they are half-first cousins or not.

In contrast to full cousins, who share two grandparents, half-first cousins share just one. This occurs when the two half-cousins’ parents are half-siblings.

Numerous people have a half-cousin relationship. Indeed, any family that had half-siblings also included half-cousins. This example demonstrates the meaning of the phrase “half cousin”: One of the siblings descended from Grandpa’s first marriage, while the other descended from Grandpa’s second marriage, and their offspring are half-siblings.

Each of us has four sets of great-grandparents, and second cousins share four sets of great-grandparents. Half-second cousins have a single great-grandparent, rather than two.

This happens when the great-grandparent remarries and has another child with the new spouse. This may also occur in the absence of marriage, such as when a child is born outside of marriage or in cases of adultery.

Half-first cousins are cousins who share just one grandparent instead of both grandparents. How is this possible? It’s more common than you might think—your half-cousin’s parent the half-sibling of one of your parents.

A centiMorgan (cM) is a unit of recombinant frequency which is used to measure genetic distance. Half-first cousins share 215-650 cM. For reference regular first-cousins share 515-1300 cM.

There is somewhat of an overlap, so if your DNA results indicate that overlapping range, you’ll need to look at any other close DNA matches that the two cousins have in common or find out how much DNA is shared between each of your parents.

As can be seen, full and half-first cousins’ DNA ranges overlap slightly. If you share between 515 and 650 cM with a first cousin, the only way to be certain you are full or half-first cousins is to either narrow things down using any shared close DNA matches or to determine the amount of DNA shared by your and your cousin’s parents.

What Is A Half-Second Cousin And How Much DNA Do We Share?

Depending on your family’s closeness, you may be acquainted with at least some, if not all, of your second cousins — whether “half” or “full.” Occasionally, we are even acquainted with the descendants of our second cousins (our second cousins once-removed).

I’ve always seen that the concept of second cousins is often where people get confused about family relationships. The addition of the “half” connection complicates matters, and so a visual explanation is occasionally required.

 A half-second cousin is someone with whom we share just one great-grandparent. Even though the amount of DNA shared is negligible, you will always share DNA with a half-second cousin.

Half-second cousins will share 30-215 cM with each other. Regular second cousins share 75-360 cM. So, just like between half-first cousins and regular first cousins, there is overlap in the amount of cM shared between half-second cousins and regular second cousins.

Just like with half-first cousins, you’d need to narrow things down using any shared close DNA matches or determine the amount of DNA shared by your and your cousin’s parents.

What Is A Half-Third Cousin And How Much DNA Do We Share?

Half-third cousins have just one great-great grandfather, as opposed to the two shared by complete third cousins. The majority of individuals discover they have eight unique sets of great-great grandparents, whereas those who share just one set are considered third cousins.

If a certain cousin shares just one great-great grandparent with you (rather than a group of great-great grandparents), this individual is your half-third cousin. As an example, there were sixteen great-great grandparents in our family. If you and your cousin share one of your sixteen great-great grandparents, you are third cousins.

A half-third cousin is a distant relative who shares just one great-great grandfather with you. Each of us likely has several half-third cousins, but DNA testing will not reveal them all, since there is an over 10% chance that we won’t match DNA with someone who is our half-third cousin.

Half-third cousins share 0-175 cM. I know that sharing zero DNA with a cousin sounds odd, but remember, you don’t actually have to share DNA to be genealogically related!

Unfortunately, this makes it tricky when trying to rule out someone as a half-third cousin since you might not share any DNA even if you two are distant cousins.

Final Thoughts

If you are interested in finding out more about your half-third cousins or any other cousins, and how closely you might be related, below we have compiled a list of some of the best resources you can use to track your heritage and map out your family tree.

Ancestry.com: A membership to Ancestry is strongly suggested, since it simplifies the process of integrating data from documents, papers, and publicly available family trees.

With a few clicks, you can easily add a large number of persons and their related data to your tree. Without a membership, you may still design a tree, but you must acquire data in other ways and then manually insert each component.

Additionally, Ancestry offers free access to millions of publicly accessible family trees, which is a substantial value. Additionally, you may contact private tree owners directly to get information about their trees or to gain access to them, which is often authorized.

MyHeritage: DNA testing, genealogy record subscriptions, and family tree hosting are some of the things My Heritage does. Because the site has a lot of records and trees, you’ll need a membership to see them. You can make an account and search for records without one.

A lot of information about a record is shown to us before we click on it, which could help us find it in a different way or make sure that they have the right papers before we subscribe. The records are real, but they aren’t as complete as those on other websites.

You can use the DNA part of the site for free if you send in your raw DNA file from another testing company. You can do this if you want to. Because they are adding more and more DNA to their growing database, there is no reason not to add your DNA to the list. Test with a different company and send the results to the website because they don’t know how to do genetic tests well.

One Great Family: If you think we are part of one big family tree, this site is very interesting. A tree grows as people give information and connect it to other trees based on the information they give. This makes the tree bigger.

For as long as there’s a free trial, it’s free. Trying to figure out how to get around the site can be a little tricky. Even so, you might take advantage of the free trial period while you’re there to see if you can learn anything about your family while you’re at the place.

Archives.com: This webpage contains a substantial amount of information. There is a 14-day free trial, which is excellent for evaluating the product and determining its value to you.

They simplify the process of obtaining a copy of an ancestor’s birth, marriage, or death certificate from the state vital records office. Additionally, you may upload or create a family tree on the site.

Although the majority of the content on this site seems to be available elsewhere, having it all in one place is useful. At the very least, it provides an opportunity to look about.

However, it seems that this service does not have listings for areas outside of the United States, which is a drawback. This is a substantial disadvantage for those who have family members who live outside the United States.


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