If person A has had the genes dictating their sight/ the internal structure of their eyes, replaced by say, eagle eyes or cat eyes.

What happens when they reproduce with person B who has regular human genetics?

I would imagine that the genes governing eye structure in cats are incompatible with the genes governing eye structure in humans.

Would the offspring of A and B just not have eyes? Or would their eyes not form properly? Or would they maybe have one set of genes dominate the other and act as a single source of information for the formation of their eyes?

Essentially my question is what happens when two humans/animals that share the majority of their genetics (enough to count as the same species) but have key differences in certain sets of genes mate together?

  • 1
    $\begingroup$ If you want a nicer, less awful, a somewhat more predictable result keep your edits to a single gene, or even a single codon if possible. $\endgroup$
    – kleer001
    Aug 16 '19 at 22:44
  • $\begingroup$ That's genetic condition treatment in a nutshell. $\endgroup$
    – Olliroxx
    Aug 17 '19 at 18:11

There are three generals outcomes given your set of circumstances.

Outcome #1: The genes are incompatible - for whatever reason, the two genes work against each other, maybe they inhibit each other's expression, or they don't synchronize properly. In your case, you wind up with blind offspring.

Outcome #2: One gene is dominant over the other. Normal genetics take over. This is more likely to occur when you're working with altered human genetics than transposed cat genetics. In your scenario, whichever set of genes is dominant (super eyes or normal eyes) gets expressed.

Outcome #3: Co-dominance / Incomplete dominance. These are two different things entirely, either both genes are fully expressed or one gene is partially expressed, resulting in a hybrid. I lumped them together because they result in the same outcome, a hybrid. Such a hybrid, for instance, might be better-than-average eyes, or even better-than-eagle-eyes, somehow. It would not be one normal eye and one super eye.

As for what happens in your scenario, the inserted Eagle Eyes DNA would probably clash with human DNA, and the offspring would be blind entirely. Thanks to recombination and crossing over, their children would also keep passing along traces of eagle DNA, and result in a family with eye defects.

  • $\begingroup$ TL;DR: technology most likely would not pass tests on mouses. $\endgroup$ Aug 17 '19 at 9:20
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    $\begingroup$ Regarding your last paragraph, the eyes of all vertebrates are all homologous, and the genes governing their formation are pretty much the same. The differences are mostly in when, where and how much those genes are expressed during fetal development, i.e. quantitative. Thus, my guess would be that if you randomly mixed up the relevant eye development genes from, say, humans and eagles, you'd probably still get eyes. Maybe not very good eyes — the resulting hybrid individual might well end up being "legally blind" — but probably with at least some limited capability for vision. $\endgroup$ Aug 17 '19 at 10:01

Somatic mutations are not heritable.

If you want your gene edits heritable then you will need to edit the germline of the entire organism. Your edited gene parent and normal gene parent will both contribute genes to the offspring and the offspring of the phenotype will depend on dose and dominance of the edited and wild type genes it inherits.

Or a cleaner way would be to produce somatic mutants. Genetically modify only the cells of the eye. The germ cells of your edited organism remain wild type and any children will not be affected by somatic mutations in one of the parents. An example using current tech would be if I get a bone marrow transplant from my sister when I am 11. My blood cells will be female - her blood cells. Over time some of these blood cells might take up residence in various organs. But my sperm are original issue and not female sperm cells, and any children I might beget are unaffected by the fact that I have blood cells with DNA not my own.

A nice thing about this is that you cannot steal my genetic engineering prowess and breed your own creatures carrying my edited genes which I worked hard on. Genetic modifications from my lab are not heritable and die when my modified individual dies. If you like the modifications I make and want some for your individual, hire me. Or coerce me to do what you want, if you are sure you will never be turning your back on my creations.


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