Genetically speaking, am I more closely related to my individual parents, or one of my siblings, excluding identical twins?
In: Biology
It’s approximately the same. You get about 50% of your DNA from each parent. This isn’t exactly true in the sense that you, whether male or female or intersex, get all of your mitochondrial DNA from your mother, so you’re getting a little more from your mother than your father in that sense. Plus the Y chromosome is a lot smaller than the X chromosome so that means slightly more DNA from the mom than from the dad if you’re a guy. But still, you’re always getting 23 whole chromosomes from each parent, except in very rare cases, so you have 23 chromosomes from each parent, for a rough 50-50 division.
For siblings, they, too, get 50% of their DNA from your parents. In theory, this could mean you share 100% of your DNA with your sibling (if you’re identical twins). While technically you could also share 100% and not be twins just by virtue of coincidentally getting the same DNA in a totally different egg and spermatozoon, the odds of this are so small as to be impossible. Likewise it’s also in theory possible to share zero percent of DNA with a sibling because the egg and sperm that made them contained all of the DNA from your parents that you didn’t get, but that, too, has odds so small as to be impossible. So on average, you share 50% of your DNA with your sibling. It could be a little bit more, it could be a little bit less.
So while you’re basically guaranteed about 50% of your DNA being from each parent, in theory you could be even more closely related to a sibling if by coincidence the egg and spermatozoon that made them happened to contain a bit more of your same DNA than the 50% that is most statistically probable. Also, if you and your sibling are both boys, then you have identical Y chromosomes, which might push you slightly beyond 50%. If you’re both girls, then you have one identical X chromosome from your father, which can push you slightly greater than 50% similarity. If you’re boy and girl, then you have one whole chromosome each that is completely different from what the other has–Y for him, X for her, and that might push you slightly under 50% as a result.
If you do 23andMe DNA service, you can see this for yourself as it will show how much DNA you have in common with your siblings.
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