# Mitochondrial DNA **URL:** \ **Category:** Factual Questions\ **Created:** [April 18, 2001, 2:01am UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371 "2001-04-18T02:01:21Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [April 18, 2001, 2:01am UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371/1 "2001-04-18T02:01:21Z")
I have come to understand that the mitochondria…the engines of our cells…contain DNA. Does this Dna contribute to our genome? ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [April 18, 2001, 3:16am UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371/2 "2001-04-18T03:16:01Z")
The genome is defined as the entire complement of genes of an organism. This includes genes from organelles such as the mitochondria and, in plants, chloroplasts. DNA from organelles is usually treated separately from nuclear DNA, so you’ll sometimes hear terms such as “mitochondrial genome” and “nuclear genome”. You can get an overview of the mitochondrial genome of humans from these web pages: [http://www.ncbi.nlm.nih.gov/cgi-bin/Entrez/framik?db=Genome&gi=12188](http://www.ncbi.nlm.nih.gov/cgi-bin/Entrez/framik?db=Genome&gi=12188) [http://www.gen.emory.edu/mitomap.html](http://www.gen.emory.edu/mitomap.html) Note that the mitochondrial genome is degenerate. Many of its functions have been taken over by nuclear DNA. Mitochondrial DNA still encodes for its own ribosomes, tRNA, and certain proteins involved in the respiratory pathway. Here’s a page about mitochondrial biology: [http://cellbio.utmb.edu/cellbio/mitoch2.htm](http://cellbio.utmb.edu/cellbio/mitoch2.htm) Genes found in the mitochondrial genome are responsible for some rare diseases like Pearson marrow-pancreas syndrome. More information on mitochondrial diseases can be found at the web page of the United Mitochondrial Disease Foundation: [http://www.umdf.org/](http://www.umdf.org/) ---
**Author:** ![dasmoocher](https://avatars.discourse-cdn.com/v4/letter/d/dbc845/32.png) [@dasmoocher](https://boards.straightdope.com/u/dasmoocher)\ **Post date:** [April 19, 2001, 3:02am UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371/3 "2001-04-19T03:02:01Z")
I didn’t check out all the above Web-sites, but they probably give you the facts. I would just add that it’s the mito DNA that is used in such determinations as ‘did Jefferson father children by Sally Hemmings’. The egg and sperm merge to form a zygote–a diploid cell that everybody arises from. This cell needs mitochondria for energy production. The mitochondria is passed down by the mother’s eggs; a sperm cell is basically a DNA delivery system. So basically, the sperm provides half the DNA and the egg provides everything else. Since sperm dosen’t contain organelles (and the DNA in mitos) and eggs do, this maternal DNA can’t be used to trace definite paternal heritage. The caveat is that you can’t determine what male the DNA came from. To me this is why I find the case that Thomas Jefferson was the father of some of Sally Hemmings children unconvincing. Maybe he was, but the DNA evidence doesn’t prove it, no matter what one reads in the general media. All it proves is that it was some Jefferson male was–because all their mitochondrial DNA is passed down by the females in their family. Jefferson mitochondrial DNA is not unique to a particular male, AFAIK. ---
**Author:** ![troub](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troub/32/14802_2.png) [@troub](https://boards.straightdope.com/u/troub)\ **Post date:** [April 19, 2001, 3:25am UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371/4 "2001-04-19T03:25:36Z")
It is my understanding, and I may of course be wrong, that the sperm does indeed contain mitochondrial DNA, but that it is contained in the midpiece of the sperm cell (the section between the head and the flagellum (tail) of the sperm). Since the midpiece and tail “break off” and only the head enters the egg during fertilization, the sperm does not contribute any mitochondrial DNA to the zygote. ---
**Author:** ![dasmoocher](https://avatars.discourse-cdn.com/v4/letter/d/dbc845/32.png) [@dasmoocher](https://boards.straightdope.com/u/dasmoocher)\ **Post date:** [April 19, 2001, 4:02am UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371/5 "2001-04-19T04:02:48Z")
troub–yeah, the flagella biomotor needs mitochondria to power itself–sperm are energentic little creatures (and these mitochondria would contain DNA). But, baically you’re right, these mitochondria only power the sperm; they don’t contribute to the zygote. ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [April 19, 2001, 4:03am UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371/6 "2001-04-19T04:03:01Z")
**troub** is correct that the sperm contains a single mitochondrion in its midpiece and therefore does have mitochondrial DNA. Indeed, it is this mitochondrion that powers the tail, which allows the sperm to swim. The midpiece and the tail are left behind during fertilization, so only the mother contributes her mitochondria to the offspring. **647** is also correct that the DNA tests show that _a_ Jefferson - but not necessarily _the_ Thomas Jefferson - fathered Eston Hemmings, Sally Hemmings’s son. However, the test didn’t involve looking at mitochondrial DNA but rather the Y-chromosome. The Y-chromosome is one of the sex chromosomes and is passed only from father to son. Thomas Jefferson therefore had the same Y-chromosome as his brothers (if any), his father, his uncles, his nephews (if any), his paternal male cousins, etc. [http://www.people.virginia.edu/~rjh9u/tomsally.html](http://www.people.virginia.edu/~rjh9u/tomsally.html) > [@](#): > > There were 25 men within 20 miles of Monticello who were all Jeffersons and had the same Y chromosome. And 23 of them were younger than Jefferson, who was 65 years old when Eston was conceived. ---
**Author:** ![dasmoocher](https://avatars.discourse-cdn.com/v4/letter/d/dbc845/32.png) [@dasmoocher](https://boards.straightdope.com/u/dasmoocher)\ **Post date:** [April 19, 2001, 4:23am UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371/7 "2001-04-19T04:23:03Z")
Good link Terminus–I answered off the top of my head and I was pretty sure T. Jefferson didn’t have a surviving male line. Thanks. ---
**Author:** ![edwino](https://avatars.discourse-cdn.com/v4/letter/e/35a633/32.png) [@edwino](https://boards.straightdope.com/u/edwino)\ **Post date:** [April 19, 2001, 5:02am UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371/8 "2001-04-19T05:02:30Z")
One thing to add, yo. Certain diseases (especially ones involving energy-sucking tissues like muscle and brain) are based in mutations on the mitochondrial genome. These are inherited directly from mother to child. A condition known as heteroplasmy determines how severe the condition is – the population of mitochondria in the oocyte is mixed, and some biased selection may make for a more or less diseased child. Also, there are no mitochondria in the acrosome of the sperm (the bit that merges with the egg), and the inclusion of paternal mitochondria is quite a controversial point in the field (at least the last time I looked…) ---
**Author:** ![system](https://global.discourse-cdn.com/straightdope/original/2X/e/e489c3b7d8fce19c4b355dd4fc3f88cc39c34b87.png) [@system](https://boards.straightdope.com/u/system)\ **Post date:** [April 19, 2001, 12:27pm UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371/9 "2001-04-19T12:27:14Z")
**647** et al You should note that the conclusion reached in re the Hemmings case did not depend solely on the genetic research but rather on the entire body of evidence. The documentary evidence pointed rather strongly in the direction of Jefferson, the genetics simply bore out that direction by excluding the historically advanced “responsible parties” (i.e. the men advanced historically and by historians until recently) for Sallie’s children, notablly the Carr brothers. One needs to look, then, at the entire record. I’m sure you can follow up for yourselves. ---
**Author:** ![Revtim](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/revtim/32/1042_2.png) [@Revtim](https://boards.straightdope.com/u/Revtim)\ **Post date:** [April 19, 2001, 1:05pm UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371/10 "2001-04-19T13:05:51Z")
I think the most interesting aspect of mito DNA is the theory that mitochondria were independent organisms that joined in a symbiotic relationship with early cells. If this is true, then every single cell of our bodies is a symbiosis of two creatures! I find that neat. ---
**Author:** ![barbitu8](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@barbitu8](https://boards.straightdope.com/u/barbitu8)\ **Post date:** [April 19, 2001, 1:39pm UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371/11 "2001-04-19T13:39:40Z")
A perusal of the links that Terminus so graciously provided states that a very small percentage of sperm mitochondrial does enter into the union with the oocyte, but it is so small that it plays no part in the eventual development. Altho the MtDNA is technically, by definition, part of the genome, it has not been included in the latest hoopla concerning the mapping of the entire human genome, the reason being that it was mapped entirely years ago. ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [April 19, 2001, 4:36pm UTC](https://boards.straightdope.com/t/mitochondrial-dna/62371/12 "2001-04-19T16:36:11Z")
> [@](#): > > \*Originally posted by barbitu8 \* > **A perusal of the links that Terminus so graciously provided states that a very small percentage of sperm mitochondrial does enter into the union with the oocyte, but it is so small that it plays no part in the eventual development.** The way I was taught in biology class, oh so long ago, was that sperm mitochondria never enter the egg. More recent evidence shows that sperm mitochondria do indeed enter the egg, but they compose an insignificant fraction of the total mitochondrial population in the zygote. Even more recent evidence suggests that the egg actually [destroys](http://www.sciam.com/1999/0399issue/0399scicit1.html) the sperm mitochondria, so that you end up with purely maternal mitochondria. On the other hand, there is a [report](http://www.nature.com/nsu/990318/990318-5.html) that paternal mitochondria could survive this process, persisting in descendant populations.