What is the difference between the inheritance of mitochondrial and nuclear DNA?

Question

What is the difference between the inheritance of mitochondrial and nuclear DNA, and what advantages and limitations doe comparisons of mitochondrial DNA offer for establishing genetic relatedness?

Answer 1

Mitochondrial DNA (that is, the DNA that is inside the mitochondria, the elements inside a cell's cytoplasm which are responsible for converting nutrients into energy) is inherited directly from the mother. So whether you're male or female, the DNA in your mitochondria is identical to your mother's; hers is identical to her mother's, etc. etc. etc.

Nuclear DNA (that is, the DNA in the nucleus of a cell) contains the classic 46 chromosomes, 23 from the mother and 23 from the father. Furthermore, this DNA is from the gametes that joined when an individual is conceived -- and there is significant genetic variation in those gametes (particularly in the spermatozoa, of which so many million are present at conception). This is why all siblings don't look exactly alike -- and also, of course, why they do look similar.

The advantage for establishing relatedness is that comparing mitochondrial DNA can determine individuals with a common mother, because all offspring of the same mother will have identical mitochondrial DNA (okay if I abbreviate to M-DNA?) The limitation is that you can't use M-DNA to establish paternity; you have to use nuclear DNA (N-DNA) to establish that, and even then you'll have to look for specific genetic markers on only one chromosome out of each pair. (It's not quite as easy as sticking a Q-tip into a scanner and having the computer spit out the picture of the suspect. :-)

One interesting side effect of the discovery of the identicality of mitochondrial DNA: by studying the M-DNA of populations of isolated individuals and comparing them with populations of genetically diverse individuals, scientists have determined a rate of "drift" for M-DNA. That is, while you inherit your mother's M-DNA exactly, some copies are more exact than others -- it's the nature of DNA to introduce spontaneous mutations (that's the key mechanism for evolution, spontaneous mutation, resulting in adaptations which are more successful being better able to compete for resources than un-mutated, or differently mutated, individuals of the same species -- but that's another, even more interesting discussion).

So by calculating the rate of genetic drift for mitochondrial DNA across large populations of humans on the Earth, a number of anthropologists have determined the "common ancestor" that all humans have -- a single woman, who lived some 40,000 years ago, whose offspring were the ancestors of every surviving human on the planet. It's still a controversial theory, with some scientists believing that this is too short a time for the diffusion of homo sapiens to the various parts of the globe which we inhabit, but the biochemical evidence is quite strong. It's an intereting field.

Answer 2

mitochondrial DNA is maternally derived, where as nuclear DNA is both maternally and paternally derived. nuclear DNA goes through the process of Meiosis

Answer 3

mitochondrial DNA is transferred from the female to all offspring. genomic DNA comes from both parents

mitochondrial DNA only changes with mutations, genomic DNA is rearranged with each generation