Let me preface this by stating that I'm a third-year Bio major currently taking graduate level courses in human genetics. I took a class this afternoon on epigenetics, and a couple of the things I learned brought X-23 to mind. I confirmed my suspicions with a bit of independent research on PubMed.
You cannot, biologically, make female clones of male humans.
To cut a long paper short, X-23 has something called uniparental disomy for her maternal X chromosome (she has two copies of one of Wolverine's mother's X chromosomes, instead of a paternal and a maternal copy). For those of you who know anything about genetics, this is a very bad thing. The two copies you have of each chromosome are far from redundant. If they were, we'd have evolved monosomy long ago. In fact, you express a slightly different set of genes on each of them depending on whether you inherited it from your mother or your father. Your cells know which is which based on epigenetic modifications (addition of methyl or acetyl groups to the proteins around which your DNA is wrapped). See the problem? X-23 has two maternal X chromosomes.
Now, a funny thing about girls is that having two X chromosomes in the first place is a little iffy. We guys get along just fine with only the one. So what happens is that one of a woman's two X chromosomes is inactivated in every cell in her body, at random. If you could scan a female's X chromosomes on Cerebra, she'd come up looking like a messy jigsaw puzzle in two colours. The silencing isn't complete, but it takes care of almost all the genes on the chromosome. This happens so that girls don't end up with twice the level of protein synthesis that guys do - which would be very bad thing indeed. By now you should have figured out where I'm going with this.
Geneticists have found from case studies that neither X chromosome gets inactivated in girls with maternal X isodisomy. The cells can't tell them apart, and so both hang around transcribing gene products. And to add to the problem, the fact that both X chromosomes are genetically and epigenetically identical means that the poor girl also manifests the problems associated with having only a single X chromosome (this is called Turner syndrome, and isn't so bad in comparison; you end up with a weird-looking body, infertility, and some cognitive deficits, none of which would merit a second glance among the X-men). But having two of the same X chromosome is far worse.
To quote symptoms from the only confirmed case of functional maternal X isodisomy in the literature (the rest die as embryos, thankfully):
- Extremely short stature (in the second percentile).
- A tiny head and low hairline.
- A short neck with "webbing"
- A deformed spine.
- Swelling and deformity of the hands and feet.
- Inability to straighten fingers, elbows and knees.
- Inverted nipples.
- Lack of sexual development.
- Severe breathing problems.
- Inability to walk.
- Inability to speak.
- Profound mental retardation.
- Brain abnormalities causing seizures.
- Extreme ugliness (all right, this is a paraphrase).
- Light stripes on her skin.
- Death at age 11 from cardiorespiratory and liver failure.
So, yeah. If X-23's alive, she isn't a clone of Wolverine.