dna

[netibiza]

How come that siblings who have the same parents , have different DNA (apart from identical twins).  The father's sperm aiways has the same DNA (that's how they catch rapists, and providing he's not a chimera) the mother's DNA is always the same (that how the mitrocondrial dna is passed down through the children) so how come each child has different dna? How and where does it change?

[jake-the-peg]

Firstly there are two different DNAs the DNA in the nucleus of every cell and the mitocondrial DNA.

Mitocondria exist in our cells seperate to the nucleus and convert chemicals to energy in what's called the ATP cycle they're like little power plants.

They divide asexually like amoeba so when a cell splits the two halves have identical mitochondrial DNA - changes do occur in this but only very rarely so mitochondrial DNA is passed almost exactly unchanged down the maternal line.

Put very basically, in sexual reproduction a strand from the male DNA merges with the female DNA. Now despite everything our similarities are far greater than our differences so mostly it matches but in some places it is different and this is where different dna comes from.

I don't actually understand the process how these conflicts are resolved either in favour of one sequence of bases from the mother or another sequence from the father maybe somebody can enlighten both of us.

In terms of DNA analysis to determine a father, I believe that sequences of bases in the DNA common to father and child are identified and the outcome based on those being inherited sequences.

In criminal cases (rape or otherwise)  DNA samples from crime scene are matched with the suspect's DNA this is obviously more certain than determining paternity because you are comparing like with like.

Mitochondrial DNA will always give you an exact match on the maternal line.

I believe prince Philips Mitochonrdial DNA was used to verify the identity of the Romanov corpses because he shared a maternal line with them. 

[chakka35]

The father and the mother have 46 chromosomes each but only 23 are passed on from each parent to the child,  making up the child's entitlement of 46.

Different conceptions (either at different times or when a multiple conception occurs at one time to produce non-identical twins) produce different combinations of 23 + 23 which is why siblings resemble each other in some ways but not in all. Identical twins are caused, of course, by the splitting of a single egg after fertilisation by a single sperm, both halves of the split therefore having the same genetic code.

[Space]

a single sperm from the father only contains half of the father's DNA.
( Same thing for the mother )
otherwise children would have twice as much DNA as their parents!

[netibiza]

Thank you all very much.  Now, if  both parents are dead and the siblings (7 of them) wish to know if they have the same father (2 being in doubt) how can this be done??