Re: Why don't mitochondria have junk DNA?

rev.goetz wrote:

> John Harshman wrote:
>
>>Selection for fast replication? That's the usual idea for bacteria, but
>>do mitochondria have to replicate that often compared to the nucleus of
>>the same cell? That would depend on the lifetime of a mitochondrion and
>>its standing population in the cell. I'll have to look that up.
>>
>>If not that, then what?
>>
>>There are mitochondria with junk. In fact the control region has been
>>duplicated several times in different groups of birds, and one of the
>>copies is clearly non-functional. So it does happen. But why so rarely?
>
>
> Junk DNA is an extavagant byproduct of evolutionary processes because
> the rate of neutral mutational insertions from various types of
> repeated sequences appears to be significantly more frequent than the
> fixation rate of all mutational deletions. And I recall that only
> diploid cells have the mechanisms that generate various types of
> repeated sequences. (I do not have the time to look up the reasons for
> this.)

You would seem to be talking about unequal crossing over. That's only
one of a host of processes that generate new sequences.

> Concerning some junk DNA in mitochondria, this could have occurred by
> DNA transfer from the nuclear genome to the mitochondrial genome. I am
> not sure if I have heard of cases of DNA transfer from the nuclear
> genome to the mitochondrial genome, but I know that I heard of several
> examples of gene transfer from the mitochondrial genome to the the
> nuclear genome. So I would not be surprised to see if the reverse ever
> happened.

I don't know of any such case. Like I said, the only mt junk I know of
involves a duplication of a mitochondrial region.

.

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