Can 23andMe be Wrong About Half-Siblings?


Learning about having a half-sibling can change your life as well as the relationship with one of your parents for better or for worse. Well, it all depends on how you look at having a brother or sister from a different father or mother.

In any case, discovering the half-sibling that you have is made possible by means of a DNA test on the web such as 23andMe. About 6 to 8 weeks after submitting a tube filled with your saliva to the said site, you will receive the DNA test results.

Are you wondering if 23andMe can be wrong about half-siblings? Yes, it is possible for the genetic testing company to be wrong about half-siblings. The amount of genetic material shared by half-siblings is 25%. However, the same amount of genetic material is also shared by a nephew and an uncle or a grandchild and a grandparent. When interpreting, 23andMe may make a mistake.

23andMe, just like so many other sites on the web that perform DNA tests, have a relative finder feature. This makes it possible for you to make your family tree more complete each time a match is made.

Having a match means that you share genetic material with a person who also took a DNA test from 23andMe. While the DNA test results maybe 100% accurate, the interpretation 23andMe does is not that reliable all the time.

For instance, instead of being half-siblings, the company may say that you and the other people are uncle and nephew even though that is not the case. The good news is that there are so many other genealogy or ancestry sites out there aside from 23andMe that you may try as well.

Different sites use a different set of rules in order to establish family relationships. Some of these companies may be more accurate when it comes to identifying your relationship with a person with whom you share some genetic material.

How 23andMe Predicts Relationships

A DNA test is a science — it is being used for solving crimes, detecting diseases and illnesses that can be passed by parents to their children, and determining paternity.

These days, due to the popularity of DNA test sites, it is also being used by consumers in identifying their relatives, including those that they never thought they had.

When it comes to predicting relationships based on a DNA test, 23andMe, as well as other similar sites, simply make predictions. So, in other words, they do not use procedures that are proven by science to yield results with 100% accuracy.

In the case of 23andMe, it predicts your relationship with other people by taking a look at your autosomal DNA and X chromosome, too. Put simply, your autosomal DNA (pair of chromosomes from 1 to 22) comes from both your parents, no matter if you are a male or female.

On the other hand, your X chromosome (or sex chromosome) comes from your father only. The sex chromosomes of your mother are both Y chromosomes, while the sex chromosomes of your father are X chromosome and Y chromosome.

When two individuals have similar DNA because they obtained it from the same ancestor, 23andMe is sure that they are related to one another.

The problem is this: the said site can only make an estimation of the relationship between the two people based on the amount of genetic material that they share.

We all know that if something is just an estimation, it is not absolute. Therefore, the process of predicting relationships is not completely reliable.

More Related the More Genetic Material is Shared

As a general rule of thumb, the more genetic material you share with a person, the more related you are to one another. It simply means that the two of you have similar-looking DNA.

Half of your DNA came from your father, and the other half of your DNA came from your mother. So, in other words, you are 50% your dad and 50% your mom.

However, it is important to note that scientists say that it is not an accurate number. So, your genetic makeup may be slightly more your father than your mother, or vice versa. Worry not because rest assured that more or less, you are half your dad and half your mom.

The DNA of your sibling is also like yours — about half of it came from your father, and the other half of it came from your mother. Are you wondering how much genetic material is shared by you and your sibling? Well, scientists say that the two of you have 50% shared DNA.

Based on the numbers given above, it is easy to see how 23andMe, as well as other DNA test sites on the web such as AncestryDNA, are able to say if two people are parent and child or siblings.

Just like what was mentioned earlier, the more amount of genetic material is shared, the more related people are. You have more DNA shared with your parents and sibling than other relatives of yours. You still share some DNA with them, but not a lot.

And this is why if you have very few genetic materials shared with a person, 23andMe assumes right away that he or she is your cousin, aunt, or uncle.

Half-Siblings Share Less Than Half Genetic Material

It can be very easy for 23andMe to figure out if a person is your parent or sibling. Unfortunately, the company may have a hard time predicting your relationship with an individual accurately if not enough DNA is shared by the two of you.

This is the reason why there are so many posts on the web about 23andMe committing mistakes when it comes to identifying relationships other than parents and their children as well as siblings.

It is safe to say that the lesser DNA is shared, the more mistake the relative finder feature of 23andMe can commit. The problem is not in the result of the DNA test but in the set of rules employed in order to determine the relationship of two people with shared DNA.

Again, about 50% of your DNA is from your father, and the other half is from your mother. You and your siblings share about 50% genetic material.

Definitely, the amount of DNA you share with a person is lesser than the amount of DNA you share with both your parents and your sibling if he or she is your cousin, first cousin, uncle, aunt, grandparent, or great grandparent.

Similarly, you have lesser genetic material shared with a half-sibling. According to scientists, you and a half-sibling have about 25% similar DNA.

That is the same amount of DNA that you share with, say, your uncle or grandparent. Because there are lots of types of relatives with whom you share the same amount of DNA, which is 25%, 23andMe can sometimes get confused.

Finding a Half-Sibling on 23andMe

You are not going to have a hard time finding a sibling that you never thought you had on 23andMe. Because of the amount of genetic material that the two of you share, it can be very easy for the company to identify whether you and the other person are siblings based on a simple DNA test.

If it is a half-sibling that you want to know about by means of a DNA test provided by ancestry or a genealogy site such as 23andMe, feel free to fill a tube with your saliva and ship it to the service provider of your choice.

As earlier mentioned, you and a half-sibling have about 25% similar DNA. Based on this scientific fact, 23andMe or any other site is going to look for a match and check if there is a match that shares the said amount of genetic material with you.

However, this poses a problem, especially if the set of rules used by the site is not that accurate or reliable.

It is because of the fact that an actual half-sibling of yours whose DNA profile is saved on the DNA database of the company may be mistakenly identified as an uncle, grandparent, or first cousin of yours.

Similarly, 23andMe may make a mistake by saying that a relative of yours is your half-sibling, even though that is not the case. This can happen for as long as you and the other person have about 25% shared DNA.

As you can see, it is not the DNA test itself that can mess with your family tree, but the way the company tries to identify the relationship between the two of you share. So the bottom line is it’s important for ancestry or a genealogy site to interpret correctly.

Different Sites Tend to Provide Different Relationship Results

Are you frustrated because 23andMe says that the person is your half-sibling when, in fact, he or she is your first cousin or actually a full sibling?

Or are you upset that 23andMe says the individual is your aunt or grandparent when, in fact, he or she is proven a half-sibling of yours? Fret not because mistaking one DNA match for another can happen.

As a matter of fact, if you comb the web, you will surely come across posts about such a very common issue.

Getting a DNA test from a different site may leave you surprised at the moment that you get the DNA test results. It is because you may actually get an outcome that is completely different from that which you obtained from 23andMe.

Yes, different ancestry or genealogy sites may actually provide different results!

No, it doesn’t mean that each one of them gets different DNA test results. Again, DNA testing is a science, and it is 99.9% accurate provided that it is carried out in the correct manner.

The problem is not the DNA test, but the way ancestry or genealogy sites interpret results. They do so by taking a look at the amount of genetic material two people in their DNA databases share.

These sites are not going to have a hard time figuring your relationship with your parent or sibling because the two of you have lots of DNA shared.

On the other hand, these sites may have trouble identifying your exact relationship with a person if you share less than 50% of DNA with him or her.

As earlier stated, you and a half-sibling of yours share 25% DNA. However, you also share the same amount of DNA with so many other relatives of yours, from your uncles, grandparents to cousins.

Obtaining a Second Opinion From a Different Site

Not entirely happy or content with the DNA test result from 23andMe as well as its interpretation? Then you may consider choosing another ancestry or genealogy site and submitting a tube of your saliva to the company.

Again, it is very much possible for different sites to have different results. It all has something to do with the set of rules they use to make an interpretation of the relationship between two people with matching DNA test results.

Getting your DNA tested by another site is just like getting the diagnosis of another doctor if you are not happy or confident with the diagnosis of the first one that you approached.

So, in other words, getting your DNA tested by a site after having the DNA test results from 23andMe is just like getting a second opinion.

The good news is that it is virtually impossible for you to run out of reliable and easily accessible ancestry or genealogy sites to turn to these days. It is for the fact that they are highly popular as a lot of people go for the services they offer.

Ancestry DNA, GEDmatch, and MyHeritage are just some of the most well-known sites around. This means that they have many customers, and thus they have bigger DNA databases than the rest.

As a general rule of thumb, it is a good idea to have your DNA tested by a site with a massive DNA database. Such makes it possible for you to build your family tree faster, thus allowing you to get to know yourself and your family better.

Unfortunately, getting your DNA tested does not come free of charge. This means that you should be willing to spend a huge sum of money if you are determined to learn more about you and a half-sibling of yours.

Family Secrets Will Surely be Revealed

In your quest to get to know a half-sibling you didn’t know you had or prove once and for all that a person who seems like a half brother is, in fact, your half brother, you may have come across related stories on the web.

Perhaps you have already run into the post of a woman on a well-known discussion site. In the said post, she said that she and her sister both had their DNA tested by 23andMe.

And when the DNA test results came, they compared their respective results. According to 23andMe, they only share 24.7% DNA. Earlier in this article, we mentioned that siblings share 50% of genetic material because they are, after all, from the same set of parents.

Evidently, the woman and her sister are not full siblings but instead just half-siblings. If we consider the DNA test results provided by 23andMe as completely accurate, then it is for certain that the two of them are not full siblings.

In order to have the problem resolved, it is a good idea to follow the recommendation above, and that is to get a second opinion from a different ancestry or genealogy site.

It is also very much possible for the woman and her sister to ask their parents to undergo a DNA test. However, this can surely rattle the whole family as soon as the DNA test results come out and say that the sisters are actually just half-sisters and not full siblings as they thought all their life they were.

It is for this reason why most ancestry or genealogy sites warn their customers that having their DNA tested could lead to stress and anxiety that could have terrible consequences on family relationships.

Just Before You Go…

There are many popular ancestry or genealogy sites these days. And one of the most popular is the 23&Me. If currently you are on the hunt for a half-sister or you would like to know if a person is actually your half-sister, you may use the site for the job.

However, just like with the experience of many of 23and Me’s customers, it is not that reliable when it comes to predicting half-sibling relationships.

It is completely up to you if you would like to have your DNA test performed by 23andMe.

If you are not pleased with the DNA test results because it seems inconclusive or too shocking, you may consider having your DNA test performed by another ancestry or genealogy site.

If the DNA test results from the new company are similar to what you obtained from 23andMe, then there is a huge possibility that the DNA test results you got from the latter were accurate after all.

Ryan Sanders

Ryan Sanders is an aspiring genetics science enthusiast. His journey started with curiosity about his roots. He keeps learning more about genetics every day.

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