Wikipedia: "In genetics, paternal mtDNA transmission and paternal mtDNA inheritance refer to the incidence of mitochondrial DNA (mtDNA) being passed from a father to his offspring. Paternal mtDNA inheritance is observed in a small proportion of species; in general, mtDNA is passed unchanged from a mother to her offspring, making it an example of non-Mendelian inheritance. In contrast, mtDNA transmission from both parents occurs regularly in certain **bivalves**."
(Bivalves, not human beings.)
"In human mitochondrial genetics, there is debate over whether or not paternal mtDNA transmission is possible. Many studies hold that paternal mtDNA is never transmitted to offspring. This belief is central to mtDNA genealogical DNA testing and to the theory of mitochondrial Eve. The fact that mitochondrial DNA is maternally inherited enables researchers to trace maternal lineage far back in time."
(Is this what your argument is about, MMaddi, AnnTurner, & those defending your statements about mtDNA inheritance?)
AnnTurner's post to me: "Recombination on the Y is generally limited to the very tips of the chromosome, which do exchange material with the X chromosome (not mtDNA). The bulk of the Y chromosome (and the place where the genealogical Y-STRs reside) is called non-recombining Y (NRY), and this is passed from father to son every generation."
(Here he missed the whole point of my post: that in Humans, mtDNA is inherited virtually unchanged from the maternal lineage & doesn't recombine; & he also doesn't refute my own statement that yDNA does recombine. I was talking about how mtDNA affects the percentage of unchanged familial DNA over many generations.)
Here AnnTurner claims: "Women can pass on the exact same X chromosome they inherited from their mother OR their father, but more often it is a combination of the two. Thus in most cases, each child will inherit a somewhat different X chromosome from their mother, a mixture of the X's from their maternal grandparents.. Fathers have only one X chromosome to pass along, so sisters will inherit identical X's from him."
(Again AnnTurner missed my point: about the role mtDNA plays in inheritance & how that might affect the amount percentage of DNA retained by an individual after a number of generations - that it must be a relatively fixed figure; because mtDNA is inherited unchanged/unrecombined through the direct maternal lineage.
Instead he veered off into lecturing me about chromosomes & other various aspects of genetics. Ok, I'm not a biologist, doctor or geneticist - not even a genealogist; but why would I take someone seriously, who doesn't understand how mtDNA functions, when that was the very point of my first statement? Facts are facts: 1) a Human mother carries in her cells one X chromosome from her own mother & one X chromosome from her father's own mother. 2) Ovum are cells
3) However a Human mother donates to her children only the mitochondria she inherited from her ~own mother~. Do you really believe that mothers may inherit their mothers' mitochondria from their fathers' mothers? Do you really believe that a woman's mitochondria is a combination of that of her own mother's plus that of her father's mother? It isn't. Mitochondria - as you kindly pointed out - is in a class of it's own.)
Wikipedia again, because I'm tired now & it's so much faster: "Since the father's mtDNA is located in the sperm midpiece (the mitochondrial sheath), which is lost at fertilization, all children of the same mother are hemizygous for maternal mtDNA and are thus **identical to each other and to their mother**. Because of its cytoplasmic location in eukaryotes, **mtDNA does not undergo meiosis** and **there is normally no crossing-over**, hence **there is no opportunity for introgression of the father's mtDNA**. **All mtDNA is thus inherited maternally**; mtDNA has been used to infer the pedigree of the well-known "mitochondrial Eve."
(My OP's ~point~ was that we would tend to inherit a certain relatively fixed percentage of DNA - mitochondrial DNA, specifically - regardless of how many generations we go back in our direct maternal lineages. That would have to be the case, if as so many real experts have already pointed out what I tried to get across to you all at the start: mtDNA is inherited ~unchanged~ through the maternal lineage. I believe "unchanged" means that very little if any of the original mtDNA would ever be lost, under normal circumstances. The only very rare exceptions might be such things as random mutations.
I'm dismayed that talking to a non-professional is so confusing for you; I may not know everything that you do, but how could you miss my point? You took the conversation away from the OP's question, & tried to school me in biology.
Unfortunately many of yours & some statements which followed, by posters defending you, continue to insist that Human mtDNA "typically" recombines or is inherited paternally - it doesn't & it isn't.)
Wikipedia: "Over the last 5 years, there has been considerable debate as to whether there is recombination in human mitochondrial DNA (mtDNA) (for references, see Piganeau and Eyre-Walker, 2004). That debate **appears** to have finally come to an end with the publication of some direct evidence of recombination. Schwartz and Vissing (2002), 2 years ago, presented the case of a 28-year-old man who had both maternal and paternally derived mtDNA in his muscle tissue – in all his other tissues he had only maternally derived mtDNA. It was the first time that paternal leakage and, consequently, heteroplasmy was observed in human mtDNA. In a recent paper, Kraytsberg et al (2004) take this observation one step further, and claim to show that there has been recombination between the maternal and paternal mtDNA in this **individual**."
(I cited this case in a prior post, linked to another website.)
Wikipedia: "Some sources state that so little paternal mtDNA is transmitted as to be **negligible** ("At most, one presumes it must be less than 1 in 1000, since there are 100 000 mitochondria in the human egg and only 100 in the sperm (Satoh and Kuroiwa, 1991).") or that **paternal mtDNA is so rarely transmitted as to be negligible** ("Nevertheless, studies have established that **paternal mtDNA is so rarely transmitted to offspring that mtDNA analyses remain valid**..."). **One study** **stated** that **about 1–2%** of a person's mitochondria can be inherited from the father."
(That last study mentioned above was the same one done by Schwartz & Vissing, involving the one individual with mixed mitochondria in his muscle tissues...published in New Scientist, 2002.)
Wikipedia: "The **controversy** about human paternal leakage was summed up in the 1996 study 'Misconceptions about mitochondria and mammalian fertilization: Implications for theories on human evolution'. The following quotation comes from the abstract to that peer-reviewed study printed in the Proceedings of the National Academy of Sciences:
'“ In vertebrates, inheritance of mitochondria is thought to be predominantly maternal, and mitochondrial DNA analysis has become a standard taxonomic tool. In accordance with the prevailing view of strict maternal inheritance, many sources assert that during fertilization, the sperm tail, with its mitochondria, gets excluded from the embryo. This is incorrect. In the majority of mammals — including humans — the midpiece mitochondria can be identified in the embryo even though their ultimate fate is **unknown**. The "missing mitochondria" story seems to have survived — and proliferated — unchallenged in a time of contention between hypotheses of human origins, because it **supports the "African Eve" model of recent radiation of Homo sapiens out of Africa**.”'
(So, do you agree with the above statement published in 1996 by F. Ankel-Simons & JM Cummins, because you wish to dispute the "'African Eve' model of recent radiation of Homo sapiens out of Africa"? If so, there is scanty evidence to support such a view. mtDNA proves that Humans probably originated somewhere in that geographical region.)
Wikipedia: "The mixing of maternal and paternal mtDNA was **thought** to have been found in humans and chimpanzees in 1999. **However, there has been only a ~single documented case~ of human paternal mitochondrial DNA transmission, and it was linked to ~infertility~.**"
(I mean please, people: that was my whole point from the beginning. You are basing your opinions about mtDNA on nothing of any real substance. Btw R1a1a: Hinny's are infertile & far more rare than mules, but you knew that.)
MMaddi quote: "I've quoted three points in your post where you seem to imply that somehow mtDNA and the x a woman receives from her mother are the same thing. Do you realize that mitochondrial DNA and the x chromosome, in both the male and female, are separate types of DNA? In fact, mitochondrial DNA isn't even located in the nucleus of cells, where the x, y and autosomal chromosomes are located. And Ann is entirely correct that the x a woman receives from her father and mother can and, most often, do recombine."
(Missed the entire point. Don't the chromosomes an individual receives from each parent determine the individual's phenotype or is it genotype? Wouldn't the phenotype?/genotype? of an individual include which mitochondrial DNA it inherits? My eyes aren't in my X chromosome, either, but their phenotype/genotype - sorry - is. I already cited literature which proves that women carry one X chromosome from their own mothers & the other X chromosome is from their paternal grandmothers. How would the X received from their fathers ever be capable of carrying their own mothers' mitochondria, which women then pass along to their own children?)
johi quote: "Sorry, there are a number of misconceptions here so I will just address the above. The statement is incorrect, women typically pass on a recombined X, not a selective maternal line X. It is largely a random process."
(Sorry johi, again your claim doesn't make sense in light of the fact that women normally transmit their maternal lineages - mtDNA - virtually unchanged & unrecombined over vast numbers of generations & among all of their respective offspring. So since children receive only the unchanged/unrecombined mitochondria of their own mothers - how in the world would they get that through either the X chromosome that their mothers inherited ~paternally~, or through recombined X's, during fertilization? It only requires one out of the two differing types of X chromosomes from any given mother, combined with the one X or Y chromosome received from the father, to make babies.)
Wikipedia: "According to the 2005 study 'More evidence for non-maternal inheritance of mitochondrial DNA?', heteroplasmy is a "newly discovered form of inheritance for mtDNA. Heteroplasmy introduces **slight** statistical uncertainty in **normal** inheritance patterns." Heteroplasmy may result from a **mutation** during development which is propagated to only a **subset of the adult cells**, or may occur when two slightly different mitochondrial sequences are inherited from the mother as a result of several hundred mitochondria being present in the ovum."
(IOW, heteroplasmy - and also paternal leakage of mtDNA - are apparently extremely rare anomalies. Not "typical", as many of you have wrongly suggested.)
Wikipedia: '“Multiple types (or recombinant types) of quite dissimilar mitochondrial DNA from different parts of the known mtDNA phylogeny are often reported in single individuals. From re-analyses and corrigenda of forensic mtDNA data, it is apparent that the phenomenon of mosaic or mixed mtDNA can be ascribed solely to **contamination and sample mix up**."'
(LOL. You guys wear a person down. Most people wouldn't bother to argue with you. But big-picture, panoramic truth means a lot to me, & I always learn something in the process of these debates. Nearly every time I meet that sort of seemingly irrational & forceful opposition, I uncover something important. Now, I think I realize your motive: it seems you are supporting opposition to the "Out of Africa" theory, in this case.)
gbookhammer: "I should point out that Ann Turner is a medical doctor, and does know a bit about human biology."
gbookhammer: "You also need to know what mtDNA is. It is the DNA of bacteria-like structures that are found within cells. They are called "organelles", which literally means "little organs" and in a sense they function as organs of the cell."
(No, I don't need to know every little detail of what mtDNA is, to know what it DOES.)
gbookhammer: "Genetically, males and females are exactly alike except for one thing. If a person is male, that means he got a Y chromosome from his father...)
(In reality, male & female humans are not "exactly alike except for one thing"; because, **men have up to ~1900 fewer genes than women**. The rest of your lecture neither refutes my OP regarding relatively fixed percentages of mtDNA which might remain unchanged in a family's maternal lineage over many generations. I was talking about mtDNA's part of the equation, not the entire equation.)
NOTE: This took hours to write, gave me a headache answering so many forum trolls at one time on the exact same point. And since they have full moderator control over everything that I post (iow, they censor & discriminate against me) - I would be very surprised if it gets published. Nevertheless, I tried.
UPDATE: This forum, DNA-Forums, eventually became defunct. I don't know whether they reorganized, or what happened, but the original forum where I posted is now off-line.