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Polyjuice potions are used a lot through the Harry Potter story, and it's an established fact that it accounts for both age and gender. The only known limitation is that it is only intended for taking on the forms of other humans.

Would a man changing form into a woman (or vice-versa) have functional parts of the opposite sex? It seems to me that all of the appropriate organs would be there, as the potion is all about changing form, but it is not so clear that they would work, as this would imply all sorts of strange effects.

Is there anything canonical which addresses this?

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    It was REALLY hard to answer this question and stay PG. – Jeff May 23 '13 at 21:01
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    the only thing i could think of was oh god the fanfictions" – acolyte May 29 '13 at 20:56
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    It sounds like someone is writing a TG slashfic – Valorum Apr 13 '14 at 8:39
  • interesting question - to go a little deeper, essentially asking, does polyjuice change DNA? – NKCampbell Apr 14 '17 at 22:05
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There are only two accounts of Polyjuice Potion used to effect a gender change; all other transformations are man-to-man or woman-to-woman (or, in one case, woman to catwoman). In neither of the given examples is any explicit indication of anatomical correctness given, which is fitting for a series of novels aimed at the general PG crowd (maybe PG-13, especially in the latter half, but more the Star Wars PG-13, not the Titanic PG-13).

In Book 4, the dying wish of Barty Crouch Jr.'s mother was to free her son from Azkaban. To do so, they arranged a visit, with Barty Sr. sneaking in two portions of Polyjuice Potion. Mother and son exchanged hairs and took on each others' appearance, and Sr. snuck Jr. out of the prison, leaving the mother behind with enough Polyjuice potion to ensure the switcheroo wasn't detected until it was far too late. The dementors guarding Azkaban couldn't tell the difference, as they're blind, and both mother and son were sick at the time.

In Book 7, six other Order members, including Fleur and Hermione, take a dose of Polyjuice with Harry's hair in it to transform into him. After doing so, they all change into matching clothes, and Harry wished they'd do so a little less cavalierly:

The real Harry thought this might just be the most bizarre thing he had ever seen, and he had seen some extremely odd things. He watched as his six doppelgangers rummaged in the sacks, pulling out sets of clothes, putting on glasses, and stuffing their own things away. He felt like asking them to show a little more respect for his privacy as they all began stripping off with impunity, clearly more at ease with displaying his body than they would have with their own.

One interesting point is that both Rowling as author and David Yates as director tastefully ignored the fact that the girls would almost certainly not be wearing boxer shorts (though Yates couldn't pass up the opportunity to have Daniel Radcliffe in a bra for the movie scene). At the very, very least, Daniel Radcliffe has a few more inches at the hip than Emma Watson or Fleur's actress Clémence Poésy. So, the two possibilities, equally and hilariously embarrassing, are either that two of Harry's doppelgangers would be wearing extremely tight-fitting women's panties during the escape, or that they would have stripped naked to put on men's underwear. If Polyjuice does have the effect we are supposing, there would be an additional, rather painful restriction a bit further below the hipline, as women's undergarments are not designed with much room or elasticity in that area.

Either way, the fact that Harry's embarrassed is the best evidence we have, and while it's somewhat inconclusive it indicates, as best as could be conveyed in a PG/PG13 novel, that the transformation is "complete", as it were.

As far as "functional", that's more likely not to be the case. It's a temporary transformation, first of all, and second, the person retains their sense of self; they have to learn to adopt the mannerisms of the person they're transforming into. The movies take it one step further; people changed by the Polyjuice Potion still sound like themselves (with the notable and singular exception of Barty Crouch Jr alias Mad-Eye Moody in GoF). While I definitely wouldn't recommend a pregnant woman taking the potion, I don't think the transformation's much more than skin-deep.

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    Well said. This might be taking it too far, but what if a person (A) transformed into another (B) and managed to ... reproduce within the time-limit of the Polyjuice Potion? I would say that even A's gametes would be altered to match B's, and so the offspring would have the genetic material of B. Which would kind of make the child both A's and B's. That's just speculation, though. Not to mention, a little messed up ... – Arachno-Sapien Jan 4 '14 at 23:42
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    Regarding the underwear, I just considered it more likely that since everyone coming to escort Harry knew the plan and knew they were leaving as Harry, the girls all planned ahead and deliberately wore boxers for the occasion, even if they wouldn't normally. – Janus Bahs Jacquet Apr 15 '15 at 7:50
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    Crabbe and Goyle transform to girls in Book 6 multiple times. All we really know from those occasions, though, is that they are not particularly pleased about it, but I thought it should be noted for the sake of completion. – BolteAltamont Jan 6 '16 at 6:15
  • @BolteAltamont I had forgotten about that; the movies skip that detail. – KeithS May 31 '17 at 13:58
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As all of the major differences between human genders revolve around sexual and/or excretory function, they are not discussed in detail within the books, nor within any other canonical source I am familiar with (Rowling interviews, Pottermore, etc).

From the standpoint of realism, I am uncertain. The female-to-male situation is relatively straightforward - men continually produce sperm, and as a natural part of the male biology, they would be capable of producing and emitting it, given the proper circumstances.

The male-to-female case, however, leaves us with some issues. Women do not continually produce reproductive materials. Once a month, an egg (which has existed since the woman's birth) becomes viable for a short period.

It would be simplest to assume that the polyjuice potion, when used for a female target, transforms the drinker into that female at a non-fertile point in her monthly cycle (such as the start, immediately after the woman's last period would have ended. It would also be easiest if the potion reset you to this point each time you drank it. Were that the case, the drinker could not become pregnant and would not suffer a monthly cycle, no matter how long they went without reverting to their normal form.

As there is nothing canonical which addresses this question, I am going to assume (largely because any other path leads to tragedy that doesn't seem in keeping with Rowling's ideals) that the polyjuice potion continually sets the subject of a female transformation to an infertile state.

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  • Likely transforming into another person makes you infertile for the duration of the transformation, regardless of sexual changes. Otherwise, what would happen to the reproduction cells at the end of the transformation? Would they disappear or revert to your natural ones? Would this change their DNA? What if you fertilized an embryo: what would become of that new DNA, regardless of your original sex? – Xantec May 23 '13 at 21:07
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    My expectation is that your body would become theirs for a short time, and that anything that had separated from that body (for example, an arm, a hair, or sperm) would not revert. I wonder if a lost hair would be usable for another batch of polyjuice, though. – Jeff May 23 '13 at 21:14
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    @Jeff Probably not, given that Barty had to restrain his victim and keep on harvesting samples. If there was an easier way he would have taken it. – Tacroy May 23 '13 at 22:32
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    @Tacroy - so JKR's biology is as shoddy as JKR math :( – DVK-on-Ahch-To May 24 '13 at 13:45
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    Barty Crouch's transformation into Mad-Eye Moody involved the disappearance of an eye and a leg, both of which reappeared when the effects wore off under Dumbledore's questioning. Therefore, external organs, at least, are perfectly reversibly affected by the potion. As the potion's effects only last an hour from the last dose, there's never been any call for a deeper "examination" than simply waiting until the effects wear off. – KeithS May 29 '13 at 2:46
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Spermatogenesis (the process of a progenitor cell turning into a free-swimming wriggly) takes two and a half months.

Oogenesis (the process of ovum-formation) only occurs at one point in a woman's life, before or just after birth.

None of these times overlaps with the duration of effect of polyjuice potion.

Whatever happens to the (ahem) gonads during the transformation, polyjuice doppelgangers are infertile.

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  • There's some new-ish evidence that challenges the idea that oogenesis ceases shortly after birth. This article from 2012 gives some details on the current studies. You can search for post-natal oogenesis for more information. – Joe L. Mar 4 '15 at 4:58
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    Your logic seems sound as far as trying to rectify this against known science - but there are a lot of things in HP that completely defy everything we know. – phantom42 Mar 4 '15 at 5:28
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    You’re assuming here that the already existing spermatozoa or ova in the body of the person being impersonated would not be transferred on (or in, I supposed) to the transformed body. That seems rather a spurious assumption. If you simply become an exact physical copy of someone else’s body, why would certain subsets of their cells be exempt from that? – Janus Bahs Jacquet Feb 15 '16 at 17:58

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