If two different species with different blood bases, say iron and copper, had a child together, how would that affect their child? Which blood base would the child inherit? Could they even have a child?
Two different species implies non-compatibility for children. There are exceptions (horse + donkey = mule) but for species so different as to have completely different blood types, I'd say "nope, not going to happen."
If you want to throw "because [insert fantasy reason here]!" at it then I'd say the kid would have the same blood as the mother on account of having to share a blood supply while in the womb.
Could they even have a child? No. Not in reality. At least not with out a LOT of gene manipulation and then the child would be a freak. Spock couldn't really exist (naturally).
As stated above, it'd be impossible - but if you wanted to get really fancy, it could be an alloy of the two metals. Zinc+Copper blood bases turn into a brass based blood.
Assuming in your world this does work, what is the most plausible way to make this happen?
- fetal rejection from mismatched blood
- chromosome numbers are off
- high potential of damaged genetics
- mixed versions are often broken
The problems that occur from blood while the child is in the womb are often from the Rh antigen marker in the blood. If the mother is negative for the antigen and the baby is positive, the mother's immune system kills the baby's blood to resolve the issue. This does not usually happen in frist pregnancy If there is no blood exchange (say because of an egg instead of a womb) or if the baby has the mother's blood (Spock's blood was green, copper based, like his father, so an issue there) then there is less issues. Why there is any issue at all is odd, as the purpose of the placenta is to make the exchanges and keep the blood separate.
Chromosome count is off, and potential damage. The system of genetics that we have has parity checks and safeguards against corruption. The y chromosome is a palindrome and can fold over on itself to repair a hole. The others all are in pairs, with one from mother and one from father. Because men have only one x chrom, an X-linked recessive disorder, while inherited from the mother, will typically affect males as they do not have the other half of the x pair to correct it. With the mixing of your beings, there will be more incomplete pairs. You might also get a weird blend causing an alien version of Klinefelter syndrome where a person has xxy.
Now about the mules mentioned earlier. Mules only work one way, horse mother and donkey father. Also, mules cannot reproduce because they are genetically broken. I dont see why you cant make a humanoid mule, but they are going to have to face certain limitations on their life which might affect their personality and perspective.