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So. DNA is not arithmetic. :-)
Keep this for reference if it isn't all crystal clear the first time through.
What to take away: DNA tells you about your DNA, not about your genealogy.
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Autosomal DNA is what firms like Ancestry, 23andMe, and various others analyse.
It's the non-sex-specific DNA we all get from both our parents, who got their own from both their parents, and so on.
(The other kinds are:
- Y-DNA, the male (Y) DNA that is passed exclusively from father to son, with little variation between generations
- mtDNA, the female (mitochondrial) DNA that is passed from mother to child, but only women continue to pass on to their own children)
When I say "DNA" in what follows, I mean "autosomal DNA". The kind everybody here has had tested.
One big question that everybody has is:
How can my DNA results (ancestral origins) vary so much from my brother's / sister's?
Here's how.
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Let us say your four grandparents are:
- maternal GM - 100% Nigerian
- maternal GF. - 100% Somali
- paternal GM - 100% Iroquois
- paternal GF. - 100% French
We all get 1/2 of our DNA from our mother and 1/2 of our DNA from our father.
So your mother's DNA is 50% Nigerian and 50% Somali.
And your father's DNA is 50% Iroquois and 50% French.
So far, so easy.
Now here's where the trick comes in.
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It seems counter-intuitive that siblings can have such different DNA.
BUT -- if you had the same DNA as your siblings, you would be ... identical twins.
The only people who have DNA identical to another person's are identical twins -- because they are the product of a single sperm + a single egg that made a single cell, which divided to make, eventually, two babies.
In fact, your mother doesn't have the same 50% of her parents' DNAs as her siblings do.
The sperm and egg that united to produce her each carried a different 50% from the sperm and egg that united to produce her sister.
Ditto your father. He got a different 50% of each of his parents' DNAs from the 50% his brother got.
So while, in their case, the ancestral origin of the DNA is all the same, it's in different amounts, carrying different characteristics.
Your father might be short and his brother tall, or your mother have an inherited genetic disease and her sister not.
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Now comes you.
Your DNA might have a big dose of your paternal grandmother's, while your sibling's DNA has a big dose of your maternal grandfather's.
You are going to get 50% of your DNA from your father. But there is almost no chance that it will be made up of half Iroquois and half French. It will be a blend of the two, but it could be 90% Iroquois and 10% French.
Ditto for the 50% of your DNA that you get from your mother. It could be any combination of her Nigerian and Somali DNA.
So your own result could well be:
45% Iroquois (from your father's M)
05% French (from your father's F)
20% Nigerian (from your mother's M)
30% Somali (from your mother's F)
You might look like a child of African and North American Indigenous parents.
But -- your sibling might look like a child of African and European parents.
You then have a child with someone who is absolutely 100% English on all sides.
The child's DNA will be 50% English.
But what the child gets from you could be any imaginable combination of your DNA.
Despite the percentages you have from each parent (above), the 50% you pass on could be:
05% Iroquois
25% French
05% Nigerian
15% Somali
... and your child might look more like your sibling than like you.
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Okay, you're lost.
Let me put it this way:
What your DNA tells you is not who/what YOU are, or who/what your ancestors were. It tells you what your DNA is.
In this case, it doesn't tell you that 15% of your ancestors were Somali or 5% of your ancestors were Iroquois. The fact is, as you know from irrefutable evidence about your grandparents, that "you" are 1/4 Iroquois, 1/4 French, 1/4 Nigerian, and 1/4 Somali. It's just your DNA that isn't.
You could have a situation where, by the time your child appears, one of the grandparents' DNA contribution has, by random chance, become virtually negligible.
Although 12.5% (1/8) of the child's great-grandparents was French, only 2% of the child's DNA is French.
But .... your second child might have got a bigger dose of French DNA, just because of the random sperm or egg the child got from you.
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Here are two examples from my personal experience.
My friends Dick and Jane had two kids.
Dick's mother was black and his father was white. He was medium in pretty much every way, and looked biracial in an ordinary way.
Jane was about the whitest person I'd ever met: short and slight with translucent porcelain skin that freckled, strawberry blonde hair, blue eyes.
Daughter Sally looked Mediterranean. Short and stocky, olive skin, straight dark hair, dark eyes.
Son Billy looked biracial. Tall and gangly, brown skin, curly auburn hair, light brown eyes.
They didn't look related at all.
My own family.
Parents Cliff and Mae (I will call them), both all English, had four kids.
Cliff had black hair and pale sea-green eyes.
Mae had strawberry blonde hair and pale blue eyes.
Four children all have varying shades of brown hair, some tending to the "golden" end, and brown eyes, some with a bit of a hazel tinge. (But I'm the most "golden", and have the second darkest eyes.)
We are a scientific oddity. My sister's grade 10 science teacher said our father was the milkman.
More recently, science has shown that each of our parents must have had just enough brown eye alleles (bits) in their DNA that the brown didn't overwhelm the blue in themselves, but when passed on in full by both, and combined, produced brown-eyed children. That's very unusual in itself, but the fact that all four of us are brown-eyed is virtually a miracle.
My nephew's father (my brother) has the darkest brown eyes and hair of us all; my nephew's mother was a pale blue-eyed Scottish strawberry blonde. The result should definitely have been a brown-eyed brown-haired child, since brown outweighs blue. In fact, my nephew has dark auburn hair and dark blue eyes. My brother didn't pass on enough brown.
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So the DNA of my siblings and me say we should be blue- or green-eyed, probably with black hair. The facts say otherwise.
And your ancestral-origins DNA results can be just as off base. :-D
The DNA may
- show little or no evidence of what you know to be a fact about your ancestors
or
- show evidence of something ancestral that is present in a much larger proportion (and therefore looks more recent) than it is in your tree (if there is any evidence of it in your tree at all).
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Since teenage I found genetics fascinating. Although we inherit 50% of our genes from each parent, some genes will be dominant to others and will be expressed and others will be recessive to others and not expressed and basically exist to be passed on to the next generation without being 'visible' so to speak. It is possible for a recessive gene to be passed down many generations without being known to even exist until a child is born to parents who both have at least one copy of the recessive gene.
An example of this is my husband's thalassaemia trait. He has one copy of the recessive gene that causes thalassaemia, but it only causes illness if a child inherits a copy from both parents because it is recessive to the normal gene, which is dominant. If I had had the same thalassaemia trait and we had 4 children the odds are that 1 child would have thalassaemia (a copy of the recessive gene from each of us) and have serious health problems, 2 children would have a normal gene plus a thalassaemia gene, so classed as having thalassaemia trait and would be well and one child would have a normal gene from each of us so not carry thalassaemia forward at all. If we'd wanted children it would have been necessary for me to be tested beforehand because of the risk of creating a sick child. Having the trait means the gene isn't expressed and no-one would ever know you were a 'carrier. unless you are tested. Sickle cell anaemia is also caused by a recessive gene and both diseases are adaptations in the red blood cells that protect against malaria and are more common in those parts of the world with mosquitos.
This shows how you can inherit all sorts of genes from a parent that may or may not be expressed because you inherited more dominant genes from your other parent. These 'silent' recessive genes may then pop up in later generations depending on the genes when combined /inherited from the other parent.
I hoped to find my OH's ancestry from places with mosquitos when he did a DNA test, but nothing turned up, so maybe it's further back in his family than the ancestry DNA test goes!
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Just replying to this then I can find it again for future ref.
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Doing the same as Grannyfranny.
Kath. x
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Sister and I have similar DNA - 'Northern European', 'Celtic;, and 'Iberian'
BUT, sister has 3. something Iberian, I have 9.6..
There are 4 siblings, we have 2 brothers - I really must persuade one of them to get DNA test..
Dad (Cornish) had bright blue eyes and straight jet black hair. Mum (Suffolk and Hampshire), had brown eyes and very dark straight hair.
Brother 1 - Straight blonde hair, bright blue eyes, pale skin, but tans easily.
Brother 2 - Straight black hair bright blue eyes, fairer skin
Sister - Slightly kinkybBrown hair, blonde streaks in the sun, blue eyes, pale skin - burns in the sun
Me - Straight black hair, brown eyes, olive skin that just gets darker in the sun.
None of us look alike - though I looked like my mum when very young - but I was darker skinned.
My ex - who was best friends with my sister's boyfriend - and knew one of my brothers - was unaware I was a relation - he thought I was Spanish. :-S
Ex - Straight light brown hair, blue eyes, very fair skinned - and I have 2 children
Eldest daughter - wavy auburn hair, dark brown eyes, dark skin.
Younger daughter - Straight blonde hair, blue eyes, extremely pale skin.
Neither looks like me, or their dad
Elder daughter married a bloke with dark hair and blue eyes, and fair skin.
Elders children - Son 1 - curly auburn hair, brown eyes, dark skin - the spitting image of his mum.
Son 2 - Well, the spitting image of his grandad- we have photos to prove it
Younger daughter married a bloke with curly blonde hair, blue eyes, and fair skin.
Younger's children- Daughter 1 - straight blonde hair, blue eyes, tans easily - looks like her mum, apart from the tan!
Daughter 2 - curly blonde hair, blue eyes, fair skin, burns easily - looks like her dad
It's weird how these genes move about :-D
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