Re: Why don't mitochondria have junk DNA?


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.)

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.

.

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