I'm just wondering how a mortal ends up (born?)with the soul of a dragon. Is it some sort of karmic glitch in the universe, or some sort of personal sacrifice? Or the result of when dragons "Fraternize" with mortals(, and therefore hereditary)?

On the subject of "Fraternizing"...
Do Argonians possess a Cloaca or Separate Tracts. Do Argonians possess Copulatory Organs, spawn like frogs, or "press" like Tuataras, .
Are the other races Copulatory Organs the same as each others or are there differences?

Seems to be hereditary atleast in tradition.
Martin is assumed and hailed as dragonborn immediately in accepting his kingship.

I'm as clueless as you about dragonborns and argonian reproduction.

But for the rest of your questions, you'll be interested in http://www.uesp.net/wiki/Lore:Notes_on_Racial_Phylogeny.
Men and Mer presumably all have similar reproductive organs. Khajiit have barbed phaluses like real world felines, as described in the uncensored version of "The Real Barenziah" that appeared in Daggerfall.

The Aedra could create them as loopholes.

Argonians probably posses a cloaca, since many of their http://www.imperial-library.info/interviews-greg-keyes stem from the word and its just cooler that way. There is some info about Argonian reproduction http://www.imperial-library.info/content/forum-archive-mark-nelson, and under "more on the Hist" in http://www.imperial-library.info/content/forum-archive-douglas-goodall.

I don't know a lot about Argonian reproduction, but I think an important bit of info is something Pete Hines posted in '03:



And I have a feeling that nature of reproduction varies with anatomy, as we know that Khajiit have very different phenotypes/breeds. And I think I recall reading that the Argonians also vary in similar way. There is more than one "kind" or breed of the best races, it seems, and I wouldn't expect the anatomies to be universal within a given race.

Prior to the Skyrim trailer I would have said purely hereditary. After it though it seems like the devs are expanding the definition. If I had to guess, and that's all this is, it will end up being someone who is a champion of Akatosh, and by extension the continuation of this kalpa.

Akatosh? What about Shor? Shor's the one who has a vested interest in keeping the kalpa continuing, and has been butting heads with the god of time a lot because of this. The god of time is 2/3 more wanting to kill the world than keep it. Damn the Cyrodiilic faith!

Well it is Dragon-born not Scarab-born :shrug: Though the alignment of their interests in this case makes it a distinction without a difference in my opinion.

A Dragonborn is a person who has been chosen by the Gods and possesses the soul of a Dragon. It is not heredity nor is it something you can achieve in life, it is chosen from your birth(or some I'm lead to believe) by the Gods. And no, Martin was not a Dragonborn, he merely took the avatar of Akatosh to defeat Lord Dagon.

Interesting topic

This.

This, other than the fact that it is, however, hereditory. It ran in the bloodline of the Septims.

Proof? The Septims might have called themselves Dragonborn, but claiming a divine mandate is not equal to actually having one. Tiber is the only one certifiably Dragonborn, and his blood died out after the second emperor.

We don't know that for certain. Martin explained his deus-ex-amoletum as his own dragon-blood mixing with that found within the Amulet of Kings, further, Jauffre and Baurus (if they survive) seem convinced that he was Dragonborn. Perhaps not the most compelling evidence, but given their monastic background, I'm inclined to trust their opinion in theological matters.