Are you wondering if your DNA will match your siblings? The answer is yes, your DNA will always match you and your full and half siblings.
How Much DNA Do I Share With My Siblings?
There is no exact answer to this question. The only completely accurate exact answer to shared DNA is when you are asking about a parent and child DNA relationship, since a child inherits 50% of their DNA (exactly) from each parent. When it comes to any other relationship, even siblings, the amount of DNA will always, always vary.
There are two ways to estimate the amount of DNA that siblings share. Some people want to know a percentage, and others are interested in centimorgans (cMs), which is a term used to measure DNA.
Amount of shared DNA between full siblings
Full siblings will share approximately 50% of their DNA with each other. Each sibling inherited 50% of their DNA from each parent, but didn’t inherit 50% of each parent’s DNA… this gets confusing, right? Imagine that each parent has a deck of cards (and it automatically replenishes). You get half of the deck of cards from each parent, and your sibling gets half, too. But each of you got different cards. Some will be the same (about 50%) and some will be different (about 50%). It’s random, though, and that’s why you never know how many “cards” will match those of your siblings. That is, unless you do a DNA test.
- Full siblings will share a high amount of cMs (centimorgans). The average will be around 2600 cMs, but it could range from 2300-3900.
- Some sources say that 3900 cMs is unlikely for a full sibling match, and that it is more likely that they share less than 3100 cMs.
- The average share DNA percentage will likely range from 32%-54%.
- I share 2671 cMs with my full sibling, for example. My mother shares 2570 cMs and 2501 cMs with two of her full siblings.
Amount of shared DNA between half siblings
Half siblings have a little bit of a different situation. Since half siblings share only one parent, that means that they will only share 25% of their DNA with their half siblings. In the card example, imagine that one half sibling got 50% of their DNA from the parent that they don’t share. Then, they had to choose from the deck of cards from the parent that they do share. The probability that they chose the exact same cards as their other sibling is almost impossible – meaning that they will share far under 50% of their DNA with their half siblings.
- In terms of centimorgans (cMs), half siblings will share an average of 1750 cMs with each other (18-32%). The range is somewhere between 1300-2300.
- Other sources say that it is very unlikely that half siblings will share 2300 cMs, and place the upper number as low as 2150. That’s why it is really important to look at circumstances and documents before making a final decision that a sibling is a “half” sibling.
- Just as an example, my mother shares 1963 cMs and 1584 cMs with her two half siblings.
On the topic of half siblings, it is important to note that there are other relationships that share a similar amount of DNA. Uncles, aunts, nieces, nephews, grandparents or grandchildren, and a few other relationships, are included. If you have a DNA match that shows up in the half-sibling centimorgan range, you will need to use other methods to determine their relationship to you:
- the age of your match
- where they lived when they were born
- available documentation
- DNA testing other relatives, if possible