Are you curious to know whether or not your DNA matches that of your siblings? In this post, learn if they share any similar genetic traits as you as well as the percentages.
People with siblings often wonder whether or not they share DNA with their sibling, and studies have confirmed this fact. Indeed, brother and sister do share some overlapping genetic material.
Equally crucial, some DNA that siblings share varies significantly between themselves – this applies whether both parents are present, as in half-siblings, or only one of them exists if this case.
I myself have several full siblings but, to my knowledge, no half-siblings.
As soon as I became interested in DNA testing, my siblings were delighted that I took one – they assumed my test meant they wouldn’t need one either! Since our parents share both DNA profiles, perhaps my test meant they wouldn’t ever need to undergo one themselves!
As we found, brothers and sisters don’t share 100% identical DNA – only identical twins do!
As we will discover below, every sibling shares an varying percentage of DNA with all their siblings.
How Much DNA Do My Siblings Share? Siblings who share both parents will share 33-50% of their DNA. If the siblings only share one parent, whether that parent is their mother or their father, then between 18-33% will be shared between them.
As you may have observed, there can be significant variation in the percentage of DNA shared among siblings (full or half), meaning there is no way of knowing exactly how much you share until both take a DNA test together.
Unfortunately, we can’t predict which two siblings share more DNA based solely on who resembles each other visually.
Parent and child relationships do not typically feature an extensive spectrum of shared DNA possibilities, because children inherit 50% from both parents.
When it comes to any relationship besides full siblings, including spouses and intimate partners, DNA amounts will always vary widely and fall somewhere within the range of shared DNA percentages that I listed above.
Estimating how much DNA siblings share is possible using two different approaches. Some are interested in knowing the percentage, while others want an exact count in centimorgans (cMs), which is used as a way to measure DNA.
Below you will gain more insight into centimorgans (cMs) shared between full and half siblings.
How Much DNA Do Full Brothers and Sisters Share? On average, full siblings typically share 33-50% of their genetic makeup; this usually amounts to between 2300-3900 cMs of shared genetic material.
We typically assume that full-siblings share around 50 percent of their DNA between themselves; however, this could vary significantly; you now realize it could even be less.
Herein lies the confusion: If siblings inherit 50% of their DNA from both parents, why don’t they share 100% of it?
Each sibling inherits 50% of their DNA from each parent; however, barring identical twins, siblings do not inherit exactly the same portion from both parents as did their sibling.
Although this might appear confusing, heed my guidance and stick with me.
Imagine each parent has a deck of 52 cards (which automatically refills). Now imagine randomly selecting half the decks of cards from both parents.
Your sibling will choose 26 cards at random as well.
Keeping track of which 26 cards you picked, then comparing that list with that of your sibling’s will reveal some discrepancies as well as others that don’t align.
Statistics tell us that approximately 50% of siblings will match, while 50% may differ. It’s hard to know which cards will match your sibling’s and, thus, you never know when matching will happen!
That is, unless you conduct a DNA test.
Full siblings often share an excessive number of centimorgans (cMs, or centimorgan-seconds). On average, this will amount to 2600 cMs; it could range between 2300-3900. According to some sources, however, 3900 is unlikely in such an arrangement and they more commonly share less than 3100 centimorgans between themselves.
Average DNA sharing percentages typically range between 32%-54%; my full sibling and I share 2671 cMs each; while my mother shares 2570 and 2501 with two of her full siblings respectively.
Genes are passed down from our parents similar to playing card inheritance; each parent contains two sets of 23 chromosomes which make up our DNA.
Recombination occurs between chromosomes from each parent to create one copy from each of these parents to pass down to their offspring as their unique, single chromosome copy from that parent, while each parent passes on one unique, recombined chromosome from themself to become their unique copy from them.
Together, these two copies become a child’s chromosomes; this occurs 22 times for each numbered chromosome.
Fathers will typically pass down one full copy (non-recombined) of their Y-chromosome to each son they father and a full (non-recombined) copy of their X-chromosome to each daughter they father; females have two copies, and will pass both down via recombination to both sons and daughters.
Half Sibling DNA Share Half siblings tend to share between 1300-2300 centimorgans of DNA between them; since half siblings only share one parent and therefore 25% or so of their genome with their half siblings.
Assuming the card example used above to demonstrate DNA shared between full-siblings is accurate, one half sibling would receive 50% of their DNA from one parent who isn’t shared and then pick from their deck of cards from the parent they DO share.
Probabilities that they would choose identical cards as their sibling are extremely unlikely, meaning that they likely share far under 50% of their DNA with each of their half siblings.
Centimorgans (cMs), half siblings will typically share 18-32% in centimorgans between themselves (18-2300 cMs).
Other sources have noted that it is unlikely for half siblings to share more than 2150 cMs; thus it is essential that one investigates circumstances and documents prior to making the assumption that someone is indeed their “half sibling.”
My mother shares 1963 and 1584 cMs between herself and two half siblings.
Half-Sibling DNA Matches Can Be Misinterpreted
On the topic of half siblings, it is important to keep in mind that there are other relationships which share similar amounts of DNA such as uncles and aunts, nieces and nephews, grandparents or grandchildren as well as several others.
If your DNA matches fall in the lower portion of the half-sibling centimorgan range, other means must be employed in order to assess their relationship to you:
Determine their age, place of birth and available documents; conduct DNA testing if possible and test other relatives, such as cousins. Read this post: Are You Related or Are They Siblings? for more details.
Are You Needing Another DNA Test?
Testing multiple siblings’ DNA can reveal invaluable insight. As we now know, siblings do not share identical genomes.
Siblings will have different genetic material and ethnicity results than each other; DNA tests performed between full-siblings could reveal distant matches based on genetic material that only one sibling inherited.
Important: When taking a DNA test, having both parents take part can reveal all of the DNA you and your siblings didn’t inherit from each other – therefore making parents an excellent option if forced to choose between getting tested themselves or having siblings take one.
If you are curious to learn how much DNA you share with your siblings or what ethnicities they inherited that you didn’t, my post entitled, “Beginner’s Guide to DNA Testing: Ultimate Strategy”, could provide some help.
Conclusion
We hope that this post has provided you with enough knowledge to comprehend why DNA will always match between full and half siblings. If any questions arose from what was discussed here or you wish to share your own experience regarding siblings as DNA matches, feel free to join the discussion thread below in this post!
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