Question

I am confussed I thought only mothers have mtDNA ad the dads dont

Answer 1

Mothers pass their MtDNA to their children, but, fathers do not.   We all have MtDNA.

https://en.wikipedia.org/wiki/Mitochondrial_DNA

Comments

Well, father's sometimes pass the mtDNA but it is a rare event (see: https://cosmosmagazine.com/biology/males-can-pass-on-mitochondrial-dna).  

Actually, if my recollection from a reading a few months back is accurate, they always pass the mtDNA but it is in the tail of the sperm and it is usually destroyed during fertilization.

Answer 2

The "dads" or otherwise all males DO have MtDNA or X DNA that is inherited from their mother, it's the "X" in the XY designation for males. Dads, however, do NOT pass their X genetic information on, because the moms do that, regardless of male or female. However, what IS useful with "dad's" mtDNA is that if it is known, then you are looking at your paternal grandmother's mtDNA, which is helpful, but will be a differing lineage of yours than your own mtDNA or more specifically, you maternal grandmother's mother's mother's mother, etc, because it was given to you by your mom. That is why you can go down the paternal line using Y-DNA and all the way down the maternal line using MtDNA, but every time you cross that line of research, you have a new haplogroup to consider and find.

Comments

X-DNA is not mtDNA, nor vice-versa. X-DNA resides in cell nuclei just like autosomal DNA and Y-DNA. Each of these chromosomes comprises millions of base pairs of information arranged along a line.

mtDNA is found outside of the cell nucleus, within the thousands of cell structures called mitochondria. It is shaped like a ring, rather than a line, and it is very small — under 17,000 base pairs of information.

The statement

 Dads, however, do NOT pass their X genetic information on, because the moms do that, 

is incorrect. Dads pass their X-chromosomes to daughters, but not sons. And importantly, they pass it as essentially an identical copy to the one they have — no recombination occurs.

mtDNA is not passed down by Dads, but Moms pass it down to all of their children, including the male ones. So a male can test their mtDNA, but they cannot pass it to their progeny.

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Just quickly, mtDNA and xDNA are very different. Mitochondrial DNA is not part of the 23 pairs of chromosomes inside the cell's nucleus. Mitochondria are organelles that exist within the cell, but not inside the nucleus. All cells have mitochondria except red blood cells (mammalian red blood cells don't have a nucleus or mitochondria), and the mature ovum has the most mitochondria of any cell, as many as 600,000 in a single cell. The mitochondrial DNA molecule is absolutely tiny, as you'd expect, and replicates itself only by straightforward copying, or mitosis.

The X chromosome, one of the two sex chromosomes, is passed down from the father to daughters in whole; the daughter has one X chromosome from the father and one from the mother. A son, however, only receives one X chromosome, that from his mother. The X undergoes recombination during meiosis before it's passed along, just like any of the 22 autosomes, so portions of the mother's father's X chromosome may be inherited by either sons or daughters.

The Y chromosome and mtDNA are called "uniparental" since they are inherited from only one parent. That makes them valuable to genealogy because they can help trace patrilineal and matrilineal lines back farther than autosomal DNA alone can. The X chromosome is not uniparental, but has its own unique inheritance pattern that also distinguishes it from autosomal DNA.

Edited: Dangit! Why didn't my BarryAlert^TM go off and tell me that he'd started writing essentially the same comment? 

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I suppose that would account for both the XX in females, so that actually makes sense, thanks for correcting me. Either way, it still is the paternal grandmother's lineage one is looking at when they are talking about Dad's X genetic information.

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Yep. To be clear, all of dad's xDNA comes from his mother's side of the family; he gets nothing from his paternal grandmother, but from the perspective of the DNA test taker, yes, it would be his or her paternal grandmother's line.

The X undergoes recombination before the gamete is formed. That means the mother's X contribution is likely made up of parts of both her father's and her mother's X chromosomes. I say "likely" because experientially it seems the X chromosome in the mother will undergo crossover, or recombination, from 0 to as many as 5 times, with the average coming in at about 1.7...so either once or twice with the result of either two or three distinct chromosomal segments.

That means the material in the X can be mixed together as segments are swapped. So the father got his X chromosome from his mother, but hers was probably a combination of the father's maternal grandmother and grandfather both. And so on at each step of the lineage that involves a female. What is absolutely the case is that the father received none of his xDNA from his father's side of the family.

Blaine Bettinger offered some nice xDNA inheritance charts several years ago here.

(Before anybody gets really picky, tiny portions of DNA that join the X and the Y in males, called the pseudoautosomal region, or PAR, can undergo recombination; but those small areas are useless for genealogy. And evidence has been found--though extremely limited and that seemingly resulted in medically detrimental mitochondrial syndromes--that mtDNA from spermatozoa has transferred to human zygotes; see Luo, et al., PNAS, December 2018).

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Wow. Now I understand it better. Thanks Edison!