DNA-maternity test - could you see other relationship than mother?

[Queenie]

Hi,

I have e hypothetical question. (I'm a thriller author and am stuck on my knowlegde on DNA). I've tried to google this for a few days now, but I guess I'm doing it wrong.

So let's say a newborn is found by a couple on their porch. It's not theirs and not their daughter's so they take it to the hospital. The daughter and the found baby are tested to prove, that she is in fact not the mother. She is not.
BUT would that test be able to show any other kind of relationsip?
For example, the found baby is her sister or half sister; or the child of an estranged first cousin. Would that be visible? And to what extend? Would only a relationship be visible, or could the expert reading those test-result actually say, ok this is a close relationship like full sister. Or this is a distant relationship like second cousin?
My story would need that test to show a family relation between the baby and the daughter, but that relationship not to be the mother.

Is this possible?`

Thanks

 

[BillTre]

A detailed comparison of the baby and other people can reveal relationships other than just who the mother is.
The mother (whoever that is) should share 1/2 of her nuclear genome with the baby and all of the mitochondrial genome.
The nuclear genome is much larger than the mitochondria genome.
The mitochondrial genome is only inherited from the mother.

The father's should share 1/2 of the nuclear genome and none of the mitochondrial genome.

The same relationships hold through longer series of generations, but the percentages of the nuclear genomes get halved with each new generation (unless there is inbreeding, like incest).
Therefore, grandparents will share 1/4 of the nuclear genome.
The mother's mother will have the same mitochondrial genome in addition to the nuclear genome.
None of the other grandparents will share any mitochondrial genome with the baby because the continuous maternal line of inheritance will only go female to female.

Half siblings will share 1/2 of the nuclear genome of their common parent (could be male or female).
Mitochondrial genome will only go through the females to their descendants, which will depend on the details of the half-relationship (which parent is shared).

Cousins (children of siblings) will have parents who are siblings. The sibling parents should share 1/2 of their nuclear genomes. In producing their offspring their contribution will be additionally halved (down to 1/4) unless both of their parents are siblings (like two brothers mate with two sisters). This stuff can get more complicated.

In any case, the mitochondrial genome if shared indicates a line of maternal inheritance.
That would be the mitochondrial genome's main function in these kinds of analyses.

 

[Hornbein]

Yes, entirely possible.

People have been convicted on DNA evidence even though they have never given a sample of their DNA from to anyone. The state will get records of relatives who have paid to have commercial vanity DNA checks done on themselves. From this they get a good enough estimate of the accused's DNA to get a high confidence statistical test of match or not.

 

[sophiecentaur]

People have been convicted on DNA evidence even though they have never given a sample of their DNA from to anyone.

Isn't that more like 'arrested', followed by a test of the suspect (can they object?)

 

[russ_watters]

Isn't that more like 'arrested', followed by a test of the suspect (can they object?)

No. It's like following them around until they discard the soda can they are drinking from.

 

[BillTre]

Suspects have also been identified based on the DNA shared with their relatives, so their own personal DNA was not required. The obvious follow up would be to test the suspects DNA.

 

[sophiecentaur]

No. It's like following them around until they discard the soda can they are drinking from.

I am not familiar with PACE (police and criminal evidence) but there has to be a way that a lead from someone else's DNA gives a good indication of guilt. Other evidence may be needed, of course. The used glass trick is not the same as linking you with another family member - if the 'perp' has to be from that family.
I must spoend more time watching TV cops.

 

[BillTre]

I am not familiar with PACE (police and criminal evidence) but there has to be a way that a lead from someone else's DNA gives a good indication of guilt.

Yes, it has to do with how DNA is inherited and shared among related people.

 

[sophiecentaur]

Yes, it has to do with how DNA is inherited and shared among related people.

Of course. the challenge I answered was a legal one and not a DNA one. Unless the suspect can claim that there is a lost brother (etc.) somewhere then the 'half match' is surely taken as sufficient. For a start, they can look at other half matches between other family members. The perp is dead in the water.

 

[sophiecentaur]

The craze for DNA knowledge is a two edged sword. Many families have had upsets when the DNA pebble has been thrown into their gene pool. It's made me smile that so many rampant racists have been shown that they have antecedants of a race that they would rather not know about. Oh boy - how embarrassing when they're not 'pure English'.

 

[russ_watters]

Suspects have also been identified based on the DNA shared with their relatives, so their own personal DNA was not required. The obvious follow up would be to test the suspects DNA.

Ehhh, I'm not seeing it. Have an example? How could they identify family without their DNA?

E.g., for The Golden State killer they had his DNA from a rape kit, but didn't know who he was. They identified his family from a genealogy website and then followed his family tree to him.

 

[BillTre]

Perp DNA sequences were matched with sequences found in an on-line DB of relatives (like Ancestry, there are several other examples). Based on inheritance patterns the guy was IDed as one of maybe many possible matches.

Follow up would be a court order for his DNA and confirm the match.

 

[sophiecentaur]

How could they identify family without their DNA?

Family members with a criminal record are on database and many families will co operate with the police and give samples.

 

[russ_watters]

Perp DNA...

Ok, so when you said:

so their own personal DNA was not required.

You really mean their identity was not required, right? Because their own personal DNA/Perp DNA is what the police matched to their relatives.

 

[BillTre]

You really mean their identity was not required, right? Because their own personal DNA/Perp DNA is what the police matched to their relatives.

Yes.
Sorry I wasn't clear on that.