Preface: Would that I had a marriage such that we could just have fights about sex, money, careers and kids. Let a benevolent God make it so.
Late last night Lady Chance and I had quite the row. We’d seen X-Men 2 this weekend for the first time and out of the blue Lady Chance says (this at about 10:30PM after the lights are off and we’re drifting to sleep) something like ‘That doesn’t make sense. There can’t be traits that are only inherited along the male line.’
‘Whuzzat?’, I reply sleepily.
‘In the movie…at one point it’s mentioned that mutations are only passed along from the male parent. That’s not possible. Only the female parent can pass along traits.’
And then the row began. Myself insisting that there are traits that are father exclusive and traits that are mother exclusive and many many traits that are both.
Things escalate. The word ‘fool’ is bandied my way. And the words ‘eventually apologize’ strikes me on the chest.
Lady Chance apparently (I may be misrepresenting) believes that, because the ‘Y’ chromosome lacks a leg that the ‘X’ chromosome has that extra leg is the spot where the mother can pass along ‘mother specific’ inherited traits whereas because there’s no corresponding spot for males males cannot be the ones who pass along anything specific without female input.
Eventually things degenerated to the ‘Ask your Doper friends! You’ll believe THEM even if you don’t believe ME. But be prepared to apologize. Hmph!’
Some pillow talk, eh? Oh, my head.
Can anyone shed some light and restore balance to the marital discussion?
Something that prevented a woman from breeding would be passed down only by men. I don’t know if there is anything like that, though.
And it couldn’t be true in the film because female mutants do breed. (FTR I think he was only screwing with the father’s mind, so if it is impossible it’s one thing that isn’t a mistake in X2.)
The X and Y chromosome both have genes on them. The Y chromosome doesn’t have very many of them, though. The X chromosome is one of the larger chromosomes in the human, carrying several thousand genes. Most of the Y chromosome is dead repetitive DNA, but it does encode 78 proteins (found to date). Obviously traits can be associated with these genes, but it is quite rare. These would be passed exclusively patrilineally – father to son (so female X-men would be impossible).
Maternal transmission can occur in two ways. The X chromosome alleles are passed from mother to son, mother to daughter, and father to daughter. The mitochondrial genome encodes a few dozen proteins. Since nearly all of the mitochondria are inherited in the cytoplasm of the egg at fertilization, these are maternal. Traits associated with mutations in mitochondrial genes would be passed mother to daughter and mother to son.
Lastly, there are some complicated genetic phenomena which can cause paternal transmission. These are called imprinted genes. Imprinting is a process of DNA modification which allows genes to be turned on or turned off depending on whether they are inherited from the mother or the father. Failures of imprinting can thus be inherited from the father’s line. One could imagine that the suite of genes responsible for “X-menning” is paternally imprinted in normal people, and a failure of imprinting then causes the paternal copy to be expressed. In this case, the father would pass one allele which is normally not expressed due to imprinting. Due to the mutation, it would be expressed. A son and daughter could now both inherit this dominant gain-of-function mutation. If Rogue (female) inherited it, she would be mutant (both paternal and maternal copies expressing) but pass it normally to sons and daughters (because the female copy is usually expressed and so it ceases to be a gain-of-function). If Wolverine (male) inherited it, he would be mutant (both maternal and paternal alleles expressing) but he could pass on a mutant copy to his children (his now-paternal alleles would both be expressing).
This is probably not when the X-men people envisioned. Given the other glaring scientific mistakes made in the movies (Neanderthal and humans didn’t interbreed to the best of our knowledge, others of hundred other little details), I don’t think they gave it that much thought. It was a very enjoyable movie nonetheless, and I am looking forward to the third edition.
The major problem with that line from X2 isn’t that there aren’t genes passed down only on the Y gene (there are) it’s that if this were true then there would be no female mutants!
Let’s say we have Mutant Father, with his XY chromosones. He and Mother get down to some sweet lovin’ one night, and concieve a girl. The thing is that all girls have XX chromosones, so she wouldn’t be inheriting daddy’s mutated Y. If the mutant gene is only on Y, then only sons can be mutants, which obviously isn’t right (just ask Storm, Jean, Rogue, Mystique…)
I personally think Pyro just pulled that line out of his ass to see what reaction he could get from Bobby’s parents.
Hang on a second, I thought the pairs of chromosomes exchange genes during meiosis so if Wolverine passes an X-chromosome down to his offspring, the X chromosome contains genes from both of Wolverine’s parents, and is a mixtur of Wolverine’s own X and Y chromosome?
I imagine that if a retrovirus were engineered to introduce a mutant gene, and it happened to target a germline cell in men and happened to integrate into the Y chromosome, it could happen. One heckova gene though. But then again, for SciFi, not a terrible stretch. For accuracy they should change the name to the XY-Men.
peter morris
Both of Wolverine’s alleles become paternal alleles during spermatogenesis (the one he inherited from his mother and from his father). Likewise, both of Rogue’s alleles become maternal alleles during oogenesis. Therefore, whatever allele Wolverine passes on will be a paternal allele. He has a 50% chance of passing a mutated allele to his progeny, both male and female. Since it is presumably a dominant gain-of-function allele, this means that half of his progeny will be X-men.
Rogue has no such problem, though. Her maternal alleles are supposed to be expressed, unlike Wolverine’s paternal alleles. So if she conceives with a normal person (who passes on one of his two, normal, paternally repressed alleles), no matter what she will not pass on X-manism. Even if she breeds with another X-man, 50% of her progeny will be normal.
Here’s where it gets weird. Let’s keep with Rogue and another X-man breeding. Of the 50% of her male progeny that are X-men, half of them will only breed X-men. The other half will breed 50% X-men (like Wolverine). Of the normal non X-men half of her progeny, half of them will breed 50% X-men, the other half will breed no X-men. So of her male progeny, 25% will breed only X-men, 50% will breed 50% X-men (even though half of them are normal), and 25% will breed no X-men. Confused yet? Her female progeny have no impact on whether their children are X-men, but we expect equal gender representation in the X-men and normal progeny.
This is why I said it was a “complicated genetic” phenomenon.
Oh, I responded to the wrong post. Sorry bout that. Earthling got it right. The pseudoautosomal region (PAR) of the X and Y chromosome pairs during meiosis, and apparently there is a bit of crossing-over. There are not many genes in the pseudoautosomal region, and if the gene responsible for X-manism were in that region, it would look like autosomal inheritance (i.e. both the mother and father could pass it on to both sons and daughters, unlike X-linked traits). Furthermore, that region is truly diploid (present in two copies), so we wouldn’t see male “unmasking” of single-copy traits (like why male-pattern baldness and colorblindness predominates in males).
So Y chromosome inheritance is most definitely not how this is happening. See above post for the only plausible way for it to happen.
Because the Y-chromosome is so small and has so few functional genes, most “sex-linked” traits are only passed through the female line. Hemophilia and pattern baldness are two examples: they occur nearly always in males (because they are recessive) but are carried on the X-chromosome. Hence if we use x to represent the allele for the pattern-baldness or hemophilia condition and X for the “normal” condition, the daughter of a bald man (pattern xY) will likely be Xx and not go bald, the daughter of a hemophilac man will be Xx and clot normally, and the son will be XY (because he gets his father’s Y chromosome, and his X chromosome from his mother) and not bald or hemophilac. But the daughters are “carriers” of the trait, and chances are 50:50 that their sons will be bald or hemophiliac.
There are, however, some circumstances in which a trait can be carried in the male line:
As noted above, a few traits are on the Y chromosome.
A dominant gene on one of the other 22 chromosomes which manifests itself only in males can be transmitted in the male line (though the daughters of the man would have a 50:50 chance of being carriers). For example, my father passed on to me a gene for fine, thin-diameter head hair, both normal hair and beard (which makes shaving more of a chore than for most men). While his hypothetical daugher would have fine, thin head hair, only his son – me – would have the thin-diameter beard hair.
So, Lady Chance was right in stating a generalization, but incorrect in believing it to be true in all cases. Most sex-linked traits are carried in the female line, but a few can be transmitted down the male line.
Sigene: Hairy ears is a Y-linked gene? Something I wasn’t aware of; thanks for the info! (But if you start developing adamantium claws… ;))
Earthling
Sure thing. I’ll use upper case to designate the dominant gain-of-function, X-manism allele. Lower case is normal. A[sup]p[/sup] is a paternal allele, A[sup]m[/sup] is a maternal allele.
So Rogue is presumably A[sup]m[/sup]a with the A[sup]m[/sup] coming from her father.
Wolverine is presumably A[sup]p[/sup]a with the A[sup]p[/sup] coming from his father.
If they have children:
** A[sup]m[/sup] a**
**A[sup]p[/sup]** A[sup]p[/sup]A[sup]m[/sup] A[sup]p[/sup]a
**a** A[sup]m[/sup]a aa
So the standard 1:2:1 AA:Aa:aa thingy. BUT, big difference. Only the A[sup]p[/sup] leads to X-men. So 50% of the progeny (A[sup]p[/sup]A[sup]m[/sup] and A[sup]p[/sup]a) will be X-men. 50% (A[sup]m[/sup]a and aa) will be normal.
Now comes the tricky part. Obviously there is nothing said about gender of the children above. All of the As in the male children become A[sup]p[/sup] – they can pass on X-manism to their children even if they are not X-men themselves (so a male child of A[sup]m[/sup]a is not an X-man, but can pass on that A as an A[sup]p[/sup] because he is a male). All of the female As become A[sup]m[/sup] when they pass it on. So even X-women can’t pass on their mutations (A[sup]p[/sup]A[sup]m[/sup] and A[sup]p[/sup]a females are X-women, but they pass on all of those As as A[sup]m[/sup] which don’t cause the syndrome).
To break down the classes of male progeny: A[sup]p[/sup]A[sup]m[/sup] X-men, all progeny will be X-men A[sup]p[/sup]a X-men, half of progeny will be X-men A[sup]m[/sup]a normal, half of progeny will be X-men aa normal, no progeny will be X-men
Let me just clarify my nomenclature. Wolverine’s sperm are A[sup]p[/sup] or a, Rogue’s eggs are A[sup]m[/sup] and a. The As adopt their superscripts during spermatogenesis and oogenesis. The rest of the cells of their body presumably would both be A[sup]p[/sup]a – because they are both X-men and presumably both inherited their mutant allele from their father. Likewise, their children’s gametes would adopt a superscript per gender, but the rest of their cells would be as indicated.