solazz wrote...
Ok guys. I'm out for now. Hopefully, by the time I get back, someone will have thrown a high school biology book at alickar.
To reiterate:
You're kidding me, alickar.
The reason all races of dogs can procreate is because despite the obvious differences between races, all dogs are members of a single species, Canis lupus familiaris. They all have the same genes, the differences are in the particular variants or alleles and their combination; if the physical act works (may be impossible naturally due to size difference etc) there's no biological barrier to cross.
Inter-species procreation is only possible in several cases of mammal pairs, and only because they're genetically nearly identical.
Different species have different number of chromosomes, and the evolution went through some pretty convoluted changes to get each species where it is now. That is only the beginning of the infinite little things that have to go exactly right to ensure a child is succesfully born. The slightest change to the system results in impossibility of survival of the child. For instance, out of 23 chromosome pairs human possesses, there lack of a single member of any pair except X chromosome results in miscarriage. Only three of them can be multiplied and still allow birth of a child, each with a wide array of pathological changes.
There's almost no chance another species in the universe would evolve to even look similar to humans in real life. Procreation between species hailing from different planets (asari obviously aside) would totally ruin the already stretched science of mass effect.
So far, they're doing splendid. The things that wouldn't work in real life are pretty well covered and all serve major storytelling purposes, enabling the story as a whole. What we're debating here would serve no other purpose than degrade this careful mix of science and fiction to the level of hocus pocus.
It works in fantasy because magic is inherent there, but in sci-fi, it would violate the most sacred principles of the genre.
Now let's just let this go and debate what the quarians' approach to adoption would be

And chirality:
Umm, as for chirality in amino acids, it means all the difference in the world from a biological standpoint.
Majority of what builds our cells and bodies are proteins. It's the way they interact that causes the incredible machine we are working smoothly, from simple structural stability of our bodies to the regulation of myriad processes taking place inside us all the time.
All of this interaction is inevitably based on what shapes and conformation those proteins take, like building a jigsaw puzzle or a clockwork mechanism.
Every protein is a chain of amino acids linked together so that they assume some shape. This shape is key, as protein interaction usually works similar to a lock-and-key mechanism.
Chirality (what's hanging left and right in one particular place of the AA molecule) defines its entire geometry and shape; the difference is like between our left and right hands.The entire network, the entire clockwork mechanism, would have to be made differently because the wheels are different. If you took a random mix of both, you could never make it work because the proteins wouldn't fit together.
The only scientifically tenable way for Shepard and Tali to have a child would be to adopt one or use donor semen/surrogate mother.
Biologically engineering a child could also theoretically work in the ME universe. But not taking Shepard's DNA and building upon it.
Just drop it already!
If they do it, they'll wreck the science. Of course they can do it, but it'd make countless people die a little.