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As the title asks, is it genetically possible for a Squib to produce magical offspring, or would the Squib gene trump the magic gene in all cases? How would it be possible for a Squib to have magical children? Additionally, must a Squib come from a pureblooded union, or does the possibility of a half-blood Squib exist?

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    Biology class was a long time ago. Even then I wasn't too good at genetics. – Xantec Jan 18 '12 at 14:36
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    One or some of the many magic talent suppression genes must be on the Y chromosome, because women are so much more magical. Since female children do not inherit that chromosome, if a squib father has a daughter, she might well more magical then he has. Q.E.D. Having several daughters, I can confirm this theory to work in practice. ("Daaadddyyyy, don't you think I should be allowed to....") :) – sbi Jan 20 '12 at 10:36
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    Harry Potter and the half-blood squib – Mikasa Nov 28 '15 at 14:43
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Yes, it's possible. In fact, it's where "Muggle-borns" come from (though usually after a few more generations).

This answer cites an explanation JKR gave during a webchat (here's a transcript of the full chat):

Muggle-borns will have a witch or wizard somewhere on their family tree, in some cases many, many generations back. The gene re-surfaces in some unexpected places.

8

I would think so.

There's not much known about the genetics of magical ability.

In my answer to a related question, I pointed out that there isn't a single 'magical gene' that is off or on - if magic power is genetic there must be a number of related genes that control it.

I would think it is possible for a Squib to produce magical offspring, though it would be less likely with Muggles than with other magical beings.

It's likely that squibs result from recessive genes, and are the result of parents who both have the recessive genes (either genes which have a mutation that 'turns off' magical ability, or genes with very weak magical ability). In either of the common cases where recessive genes express a negative effect, random mutation DOES have the ability to reverse this in successive generations (though the odds are very low). More importantly, if it is driven by recessive genes then you can guarantee a child that does NOT express the recessive traits by pairing with someone who lacks the recessive genes.

That being said, I expect 'pureblood' families tend to produce very few squibs, if any at all. Their lack of genetic diversity, however, is certainly beginning to show by the time of Harry Potter, and those detriments certainly outweigh the benefits.

  • "Their lack of genetic diversity, however, is certainly beginning to show by the time of Harry Potter" - huh? None of them had long ears or horse teeth or whatever the heck Hapsburgs had – DVK-on-Ahch-To Jan 18 '12 at 15:39
  • @DVK: No, but they were being forced into more and more interbreeding - distinct familial features (such as looking like a younger version of each other) are one of the first signs of too much interbreeding. – Jeff Jan 18 '12 at 18:52
  • @Jeff That brings up some disturbing thoughts since Harry is said to look like a younger James (but with Lily's eyes). What if Lily and James were related? – pleurocoelus Jul 23 '14 at 2:54
  • @pleurocoelus Lily was muggle-born so they are unlikely to be related. – The Giant of Lannister Mar 25 '16 at 16:27
  • @TheGiantofLannister At least not closely, though JKR did say that all Muggleborns are descended from squibs. Even if she were descended from a Potter squib, there should be enough intervening generations of Muggle genes that it wouldn't be a problem. – pleurocoelus Mar 27 '16 at 12:09

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