how many dna molecules in a cell? are they all the same?

[julianawhite]

Hi guys:

I'm a new comer here. this question has been dogging me for days. could anyone please answer it?


how many dna molecules are there in a human cell? are they all the same?

if they are all the same, why different chromosomes have different number of genes?

if they are not, how does dna fingerprinting make sure two different dna, which are from different chromosomes, from one person?

Thanks in advance.

[JackBean]

There are 46 different copies of DNA in human somatic cells. They form pairs of roughly homologous, yet not identical chromosomes.

[julianawhite]

Thank you for your kind reply, JackBean.

Could you please tell me a little more?

You said "There are 46 different copies of DNA in human somatic cells", I'm wondering if these 46 different copies of DNA have different base sequence, and if they carry different number of genes?

[JackBean]

yes, they have different sequence, that's why I wrote different. OK, I should probably not write copies, but rather something like molecules, pieces, whatever.

[julianawhite]

Thank you very much, JackBean.

Your reply helps me a lot. And one more question. (I promise it is also the last one)

Since DNA molecules in a human cell are different, how do forensics do DNA fingerprinting test?

I mean, if they find one DNA molecule, which is from the murder's chromosome-1, in the crime scene, will they have to compare it with the DNA molecule from the suspect's chromosome-1？

[JackBean]

becuase each molecule contains several different DNA molecules, but every cell contains the same set (in one body)