Partho mom produces males?

My business partner has a virgin female who produces a fertile clutch every year. My business partner produced her and has owned her for her entire life, so we’re sure she’s never been with a male. Now we have three seasons worth of babies. We assumed they would all be female, but when we actually sexed them, they came out to be a 50/50 males and females. How is this possible?


In meiosis there is a process that as gemets are made, they receive that just two sex chromosomes but end up with three. Allowing for it to appear and act female but have the Y chromosome in the case of people. I also believe that is how you get a male calico cat. Hopefully @t_h_wyman or @chesterhf could explain in greater detail.

Do you mean that the dam is hermaphroditic? I was under the impression that animals like that can’t reproduce.

As in having chromosomes YXX rather than YX or XX? The Y is dominant so if it’s possible that a YXX could survive and reproduce the Y should override both X’s. However I haven’t done this in a while so I could be wrong.


That is what I mean, but that is also what is puzzling me too.

Yes right now that sounds correct but the issue with that is that animals with that condition are sterile.

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I was wondering if they would even be able to reproduce. I have another thought but let me see if I can find a source for this before I post it.

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Can’t wait for @t_h_wyman or @chesterhf to weigh in. Cause I didnt think partho worked like that. Mommy clones only, i thought.

You guys are gonna edjumacate me! :nerd_face:


From what I’ve found my theory isn’t valid. I read a little about calico cats and it seems that a YXX will still produce male cats. I’m curious that if these snakes were bred if the offspring would have different sex ratios. I would assume that the males would behave as males but have they been put with another male to see how they each react?

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I’m no expert, but based on my understanding of the mechanisms of parthenogenesis (based on this paper and a few others) the offspring should all be female, although not exact clones of the mom. They’re usually half clones, for example a lesser female producing only female normals and leucistic offspring, or a female het pied producing only normal or pied females.

Someone who is XXY (Klinefelter syndrome in humans) will still be “male” but likely experience infertility.

What is the geneotype of the mom, and what do the offspring appear to be?


Mom is a normal with only normal ancestors, babies are all normal.



So here is the thing, and Warren has caveated this to me in conversations, our understanding, based on broadly known examples, is that the YY chromosome configuration is lethal. However, the majority of those examples are in species with dimorphic sex chromosomes. In boids (and other basal Squamates), the sex chromosomes are isomorphic. So there is a theoretical possibility that you could get a YY male that was viable.

That said, the extreme abundance of female-only occurrences is very hard to get around so…

I will try and flag Warren in on this so he can weigh in, but I will not be able to do that until tonight

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Would it be possible for the female in question here to be chimeric XX/XY and self-fertilize? I’ve never heard of this happening in ball pythons, but theoretically since all their reproductive organs are internal…maybe?

Guess I’m still confused? In a partho clutch, where does the Y come from? Are you saying there was a mechanism involved during development which changed an X, or is the mom somehow carrying a Y and still female? Seems like alot of changes to convert X to Y, is the X carrying a Y “template?” :thinking: :man_shrugging:
Sorry if I’m getting the terminology wrong. I freely admit, I’m not anything close to knowledgeable professional, just an interested amateur. One of the many reasons I like the ball pythons so much. :grin:

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No… You are correct.

I got my mental wires crossed (mental note - yerba first, forums second)

Basal snakes are XY so the females are XX and all offspring have to be XX. Advanced snakes are ZW so the females are ZW and that is where I was mentally flipped because it is the WW phenotype that is, traditionally, lethal


So, either these males, more than one in the clutch, are defying odds at crazy levels, or something else is going on? Is that right?

Applying Occam’s razor for just a moment, are we certain she never had access to a male? How young could she take sperm and store it?


So, in ball pythons, the egg not the sperm is the sex determining cell. Ball pythons don’t have X and Y sex chromosomes, they have W (female) and Z (Male) where a male is a ZZ and a female is ZW.
A partho female can hypothetically throw as many males as females as far as I can tell.

No, that is incorrect. Ball pythons are XY -


Ah, ok that would definitely make things much easier. I always thought it was male heterozygous and female homozygous for the sex chromosomes. Having it be reversed makes this outcome much more probable.

So if I understand the function here, she just developed follicles, some of which normally would have been Z and some of which would have been W, but she skipped a developmental step (a final meiosis, right?) and so they had full chromosomal complements? Some ZZ and some ZW, right? So then the odds really become 50/50 since she’s the one determining sex, not the male.

Oops posted before I saw @chesterhf post

That being the case, I’m at a loss to explain the sex makeup of these offspring