Question

Firstly I could do with a brief description of mitochondrial DNA. How does the structure of DNA in mitochondria compare to animal DNA (for the sake of simplicity let's say human - some animals might have unusual DNA structure) and what living organism is the mitochondrial genome most akin to? (Circular like bacteria maybe?) and are the mitochondria within a single human homogenous?

Secondly, and most importantly to my aim, does the mitochondrial genome recombine in anyway? Is the process of recombination affected by its structure? Are there any patterns/rules in mitochondrial recombination? Is there DNA transfer between mitochondria which could have a similar effect?

I am trying to think about how male deleterious alleles can spread differently in diverged populations given potential recombination to female beneficial (or recombination away from female deleterious mutations).

Answer 1

Mitochondrial DNA is circular, like bacterial DNA, and around 16.6 Kb long. It codes for 37 genes in total but the majority of these are simply the machinery for gene expression (curiously, mitochondria have a slightly different codon->amino acid translation 'table' to nuclear DNA) and so just 13 code for proteins. Single mitochondria usually have multiple copies of the DNA.

Mitochondria are thought to be most closely related to the bacteria Rickettsia, an obligate intracellular parasite that causes typhus. Mitochondria are so degenerate, however, that they've lost nearly all the genes that normal bacteria have.

While there is some small level of heterogeneity in mitochondria in a single person because mitochondria are exclusively transmitted down the female line most people typically only start with a single clonal population of mitochondria. Because of this, there is no other mitochondrial population present that the mitochondrial DNA could undergo recombination with.

Mitochondrial DNA does undergo recombination with nuclear DNA, however, in that genes can be transfered from the mitochondria to the nuclear DNA and because of this the majority of genes necessary for mitochondrial function are now coded not on the mitochondrial DNA but on the nuclear DNA and their protein products transported into the mitochondria after translation.