Talk:Carriers

Leave it to the Professionals
I think someone should make the Quotes be "We've been Immune so far, but if I start to turn, promise you'll shoot me!" (Bill) and "Rescue 7, are you equipped for Carriers?" (Papa Gator). If you want, you can have Rescue 7's response (A-ffirmative, Papa Gator) added to the List. A Reasonable Pic should be some of the graffiti regarding Carriers, as it is hard to get a useable Picture of a Carrier. Anyone wants to add any references, do so. Stub-ifying the Article for now... 94.195.236.134 11:48, May 9, 2010 (UTC)
 * Found a better quote to use. :3 Sera404 13:48, May 9, 2010 (UTC)
 * Aces! You're pretty good at this! 94.195.236.134 19:32, May 10, 2010 (UTC)
 * I wanted to make a new heading, but this editing page didn't allow me to do it for some reason, so this will seem off topic. Are we certain that the immune even exist? So far, from what the comic states, anybody who doesn't show signs of infection is a carrier. So I was thinking that we might want to get rid of the entire carrier vs immune secttion, since both things seem to be the same.Whachamacallit 21:59, September 21, 2010 (UTC)
 * Leave it in for now; the Survivors in both Left 4 Dead and Left 4 Dead 2 obviously believed they are immune (even if they're not). Sera404 22:11, September 21, 2010 (UTC)
 * I originally added the carriers vs immune section and I too think we should get rid of the section. At the time, the concepts of immune and carrier were both mentioned in the games but any supporting explanations were conjecture and we had no confirmation of which one existed. Therefore, I thought that it was ok to explain the key differences between these two types of immunity. While either are not mutually exclusive such one-sided immunity could exist. In other words, the carrier-type may be the only type of immunity. I feel like the section is misleading and one could interpret the article as saying the immunity exhibited by a carrier is not immunity at all. By definition, immunity takes many forms including the carrier-type. The section is misleading and should be removed. Shawty71 16:01, September 27, 2010 (UTC)
 * I originally added the carriers vs immune section and I too think we should get rid of the section. At the time, the concepts of immune and carrier were both mentioned in the games but any supporting explanations were conjecture and we had no confirmation of which one existed. Therefore, I thought that it was ok to explain the key differences between these two types of immunity. While either are not mutually exclusive such one-sided immunity could exist. In other words, the carrier-type may be the only type of immunity. I feel like the section is misleading and one could interpret the article as saying the immunity exhibited by a carrier is not immunity at all. By definition, immunity takes many forms including the carrier-type. The section is misleading and should be removed. Shawty71 16:01, September 27, 2010 (UTC)

Louis & Francis as Carriers
I understand that the doctor was never shown explicitly stating in-comic that Louis and Francis are carriers, but can't we use some more hidden evidence to support this?

-When Francis first wakes up with his headache, he asks if he was hit with the butt of the gun AGAIN. Maybe he was uncooperative with the testing?

-On page 75, Louis is seen clutching his head in horror exclaiming "So we've been Infecting people this whole time?" and goes on to mention the pilot and the Slaters. How would he know this without being told by the guards who presumably heard it from the doctor? He obviously was not in contact with Zoey and Bill.

I understand there are some holes in this evidence because we haven't seen the full story, but I feel like we should include them under "Confirmed Carriers". What do you guys think? Nightmirage 19:39, September 22, 2010 (UTC)

I 100% agree with you. As you stated, there's enough evidence to be mostly certain that Louis and Francis are carriers. Or at least, there's a lot more direct evidence supporting the fact that Francis and Louis are carriers then most subject matters. I mean if we put up all those hypotheses about how the special infected come to in the Green Flu article (not that there bad, but they are nothing but hypotheses) why can't we say that Louis and Francis are carriers?Whachamacallit 19:48, September 22, 2010 (UTC)

I was the one who added the "Confirmed Carriers" section earler today. I originally had all 4 survivors as confirmed but then remembered only reading that the Doctor had really only revealed this to zoey and bill. That's why I changed it. I mean, I'm 99.9% sure they're also carriers but at the time I wrote it, it seemed that there was a lack of proof. Up until the recent comic, the carrier article itself was majorily conjecture so since it's in the process of becoming canon, I figured I should be as accurate as possible. But honestly, it would be easier to just confirm all Francis and Louis as well. I'd say do it. Shawty71 20:58, September 22, 2010 (UTC)

I guess. I mean before the Alarm is raised, Louis reacts as though he's just been told he's a Carrier as he says Francis may be the only one he can be with without killing him. What I wanna ask is that Jeff and Annie (The Soldiers) are travelling with whom we believe to be Carriers. Should we class those two as well? Chris Thorpe 21:02, September 22, 2010 (UTC)


 * PS, I would like to refer to this page's bottom-left panel where Jeff and Annie converse with each other. Chris Thorpe 21:08, September 22, 2010 (UTC)

From what I read, I was pretty certain they were carriers too. I think we should edit that in. Imperialscouts 21:12, September 22, 2010 (UTC)

Hypothesis Regarding Carrier Genes
This is my hypothesis regarding the genes for carriers, though I don't claim to be an expert. My hypothesis is that the "Carrier Gene", described by the Doc as passed down the male line, is a Y-linked gene. Such genes are rare, and only expressed in males. This explains the relative rarity of Carriers, and the fact that 75% of playable characters are male. As for Zoey and Rochelle, I suspect that a rare recessive gene exists which also causes immunity. Zoey's mother, for example, carried one recessive gene for immunity, but this was not enough. It may turn out that this immunity is different from the immunity of Carriers - a fact which may be discovered in part 3, when the Doc gets around to testing Zoey's saliva. As well as genetics, part of this theory is based on narrative convenience - it would be quite dramatic if it turned out that Zoey has a previously unknown form of immunity

Another possibility is that there is a single Immune/Carrier gene. If this gene were X-recessive, it would mean that Zoey's father was immune, while her mother only had one copy of the gene. The chance of a woman having this immunity would be 1/X^2, where 1/X is the probability that a man carries the immunity. If fewer than 10% of males are Carriers, less than 1% of females would be. As 25% of known and probable Carriers are female, I disagree with this hypothesis, but thought it worthwhile to bring up for comparison. Chamale 04:32, September 23, 2010 (UTC)

I understand that you're not an expert, but I am so please don't be offended when I tell you why that wouldn't work (although you were on the right track). Y-linked genes are not rare since they are the definitive sex-linked genes for a male. Zoey apparently has the carrier gene (since the Dr. says it to her) so if it is a hereditary father-daughter transfer, than it sounds like an X-linked recessive gene. It can't be a Y-linked (unless Zoey is a XXY which I find hard to believe) BUT, it technically couldn’t also be just an X-linked recessive either. Otherwise, it would be hereditary from the mother as well. So now we have to find a genetic trace that links father-daughter, AND father-son. This is problematic because typically a hereditary abnormality linked to the father affects the daughter, or son, but not both. Remember, the daughter ONLY gets an X from the father, and the son ONLY gets the Y from the father (outside of polyploidal examples). Therefore, any hypothesis that claims the carrier gene is solely a sex-linked gene is incorrect

But that doesn’t explain how it could work which I know was the point of your post. My hypothesis is that there is a third recessive gene involved that is not sex-linked but works in concert with the sex-linked genes. But that’s not enough, this gene also has to have a genetic factor that prevents a female from passing it on (maybe a problem during meiosis?) otherwise the gene contradicts my explanation above. Let’s put this hypothesis to work then. In this example, we’ll say that this third part of the "carrier gene complex" will be known as igf where “i” indicates carrier inhibition of infection (we’ll also assume it is recessive). A carrier is someone with a single allele (two alleles would require heredity from mother) of the igf recessive gene which link to both sex genes. A father is a “carrier” so his genes are gf-X (from father's mother) and igf-Y (from father's father). 2nd generation goes as follows: without regards to the mother’s genetic contributions, his children could be one of the following (where “gf” indicates non-carrier):

Daughter A: gf-X (Non-carrier)

Daughter B: igf-X (Carrier)

Son A: gf-Y (Non-carrier)

Son B: igf-Y (Carrier)

So, in the case of Zoey, her genetic punnet square would be gf-X from mother, and igf-X from father. Since it only takes one igf allele, Zoey is a carrier. As for Francis, Louis, and Bill, they would be gf-X from mother and igf-Y from father and would also be carriers. Realistically, this is a more plausible explanation unless someone points out something I overlooked (which of course is always possible) but I think you get the point. Shawty71 21:43, September 23, 2010 (UTC)

Shawty71, thank you for the input. It's nice to have an expert weigh in on any topic. You have figured out the genetics for immunity, if there is only one type of immunity. However, I think you haven't addressed the other hypothesis I raised, which is that two types of immunity exist - Carrier and fully immune. I'll call it the two-immunity hypothesis. It's based on my simple understanding of genetics, where I assume that 1 gene can completely determine whether someone is Immune or just a Carrier. The hypothesis is also based on dramatic license - as the Doctor never got a chance to test Zoey's saliva, it may turn out much later on that she is fully immune. I'm guessing that the Doctor hasn't tested any other females for immunity. According to my two-immunity hypothesis, Carriers are those with a dominant Y gene which makes them remain sane when infected, but contagious to others. Obviously, only males could be this kind of carrier. Females who are immune get their immunity from a pair of recessive genes on their X-chromosomes. Zoey's mother Carolyn was not immune, but carried the recessive gene for immunity. Zoey's father also had this gene on his X-chromosome, but may not have been immune.

It's possible that Zoey and Rochelle are fully immune, rather than Carriers. If Zoey's test results reveal this, it would provide good evidence for the two-immunity hypothesis. If Rochelle's father had turned into a zombie, it would contradict the Doctor's statement that immunity is inherited from the father. Another possibility, still part of the two-immunity hypothesis, is that immune females are still Carriers despite having different genes for immunity.

You've firmly established the one-immunity hypothesis, so please let me know if there are any flagrant errors in my two-immunity hypothesis. Both hypotheses are highly speculative at the moment, but it would be good to establish some testable predictions before Part 3. Chamale 03:42, September 24, 2010 (UTC)

Ahh yes, I apologize for overlooking your 2nd hypothesis.

So in your hypothesis, immunity is achieved in two ways:

- the carrier gene is actually a male-only trait since it is on the Y-chromosome. Males and only males can be carriers.

- females have rapid antigen detection which inhibits pathogen growth and you linked the cause to be a dual recessive x-chromosomes.

You presume that the doctor’s statement is invalid because there was not much time between the moments he received Zoey’s saliva to where he told her she was a carrier.

Now, I always encourage others to think outside the box and would rather not deter you from doing so. I wouldn’t say this is farfetched, nor would I say this couldn’t happen. In fact, this very well could be true but I’d like to take this a step further and dissect it some more. Immunity and genetic immune factors are generally not part of the X or Y chromosome (that’s why I suggested a third gene was involved). That’s not to say that it can’t be, but those alleles are reserved for defining sexual characteristics only. So for the sake of your hypothesis, let’s say genes in question are X and Y. Determinations of carrier and immunity would have to be based on sex. Further, males can only be carriers and females can only exhibit immunity. You also had a side mention that the immunity gene for females could extend to give carrier properties to the female meaning the carrier condition arises from a different gene in females than in males. Therefore, you are also saying that the carrier condition arises from both the mother and the father in females (because you did say it was duel allele x-linked recessive). This actually contradicts the doctor’s statement that the carrier gene is traced to only the father so I would say this side hypothesis is a problem.

I’m pretty sure that covers the main points of your hypothesis. Besides your side mention, there is nothing here that is contradictory to evidence presented in the games or comic (if foregoing the Doctor’s statement to Zoey). So to answer your question, your 2-immune hypothesis for all intents and purposes is plausible.

Having said that, and again not trying to offend you but just maybe giving you more thoughts, I’m skeptical about it because as lucid as your hypothesis is, it’s not all that credible. Not to be a hypocrite but there’s almost too much “outside the box” conclusions being made. Unless I’m mistaken, the only type of immunity that has been discussed in the games and comic is a “carrier.” This secondary immunity gene for females is not supported by any evidence in the game or comic. Not saying you are contradicting evidence (besides the doctor swab), but rather you’re trying to create an alternative without reason to do so. In other words, why create a more complicated situation? Also, I don’t think it is a safe assumption that the doctor’s diagnosis of Zoey was hastily made. A saliva swab to test for an infection probably wouldn’t take long if there is a known biochemical indicator that can be tested. Also, maybe the doctor was collecting saliva to try and harvest the disease for further testing? If that was the case, then it’s likely he would have already tested Zoey to see if she was a carrier. Also, the doctor seemed to know an extensive amount of medical information about the disease so I don’t think it’s accurate to say he’s inexperienced or has never seen a female before.

The nice thing about science is that it can always change. What I say is likely one day could become unlikely the next. For instance, your hypothesis made me realize that my hypothesis from yesterday was actually wrong. I had said that the igf gene was recessive when in fact it would have to be dominate since the scenario I presented would require exhibiting a recessive trait while having both a dominate and recessive allele. As a recessive trait, the inhibitor couldn’t dominate over the lack of inhibitor and the carrier condition wouldn’t happen. Therefore, the inhibitor gene would have to be dominating. One could argue that it could also be an example of incomplete dominance but I’d like to think that the dominance is one-sided rather than mixed. I'm sure that'll change after the next comic comes out haha Shawty71 19:22, September 24, 2010 (UTC)

You two Scientists or something? This is difficult to even translate, let alone figure out. -- ''' Chris. Problem?  BOOM-DIAH!  ''' 20:01, September 24, 2010 (UTC)

Chris: Shawty's a scientist with advanced degrees in biology. I'm just an enthusiastic high school student.

Shawty: I agree that the two-immunity hypothesis is too complicated for the available evidence. I guessed that there was a distinction based on statements by the Church Guy, Papa Gator , and the Doctor. These statements are flimsy evidence, but it was enough to make me speculate.

As you said, this'll change after the next comic comes out. We have testable predictions in place, and we have to wait until Tuesday to make observations. Chamale 08:19, September 25, 2010 (UTC)

Not too shabby for a high schooler might I add. I hope you're planning on going to college in something science related. Shawty71 11:58, September 28, 2010 (UTC)

Perhaps you two could help make this chart I made more accurate. It seems like a wasted effort to not use it, but I don't want it to be wrong. Jo the Marten ( Shriek )  ಠ_ಠ  18:19, September 28, 2010 (UTC)

That's actually some nice graphic work with that chart, good job. I think right off the bat I can tell you that for signifying recessive genes, you should use an italicized or scripted lower case letter because I can't distinguish between dominate X and recessive x (this is typical for punnet squares). While I'm sure you were planning on doing this, I figured it's worth mentioning that you should add a second square for males. Also, when you say immune, you mean carriers right? I actually have to leave right now so I'll finish this later but if we're talking about carriers, your scheme might be indicating genetic links to the mother which contradicts the doctor's statement about the gene being on the father's side. I'll elaborate later. Looks like a great start so far. Shawty71 20:41, September 28, 2010 (UTC)

I just read Part 3 of The Sacrifice, and there's no new evidence regarding the Carrier/Immune question. I think the one-immunity hypothesis (or Carriers-Only) is still the best one available. Perhaps Part 4 will give more evidence, or perhaps not. Chamale 22:24, September 28, 2010 (UTC)

My take. From what I've learned in high school, it's my opinion that the immune gene is X-linked and decided in a dominant/recessive allele setup. The doc said "Father's side" because Valve made an analogy with color blindness, which is often described as running with the men in the family due to there being way more men with color blindness than women. They're not medical experts, which is why they put such an ambiguous line in the comic. So basically I think I share Shawty's viewpoint.

Thus: Zoey's mother was a carrier of the immune gene (One 'immune' x-chromosome + one 'not immune' x-chromosome) and zoey's father was immune (one 'immune' x-chromosome and a Y-chromosome that doesn't matter in the equation). Monojin 13:00, October 3, 2010 (UTC)

About your schematic, Jo, you forget that parents have two alleles. When trying to complete their genotypes, I found that the "Two matching 'not immune' alleles = Special Infected" theory doesn't match up with my theory of an X-linked immunity gene, as infected males would either all be commons or specials. Either the special infected thing is decided by a myriad of genetic or environmental factors, or it's got no canonical explanation and is just a simple gameplay element. I'll make a variation of your diagram and see how you feel about it. Monojin 13:34, October 3, 2010 (UTC)

Sorry I've been traveling for work and unable to respond. Monojin, I appreciate your obvious enthusiasm for this topic but I regret to inform you that we do not agree completely. This may sound like I am attacking you but please know that is not my intent. My only intent is for you to understand why we don't agree and how some of what you said is inaccurate. First let’s clear this up; the Doctor’s actual line in the comic is “As for Carriers…All we know so far is the carrier gene runs on the father’s side.”Your explanation blatantly contradicts this statement since colorblindness is a trait that is linked to a gene that can come from both the mother and the father. This does not fit the "father-only" criteria clearly established in the comic. Second, I find it very misleading to just presume this statement is ambiguous. Especially when it also happens to be an important part of a rather small pool of evidence that we have to work with. So maybe Valve isn't medical experts, or are they? How do you know? I can fully admit that I don't know but at the same time I'm not out to try and make any presumptions on Valve's scientific judgements. My explanations have been formed within the confines of the evidence presented in the games and comic. However, your assumption that Valve was trying to link carriers to color-blindness via recessive x's is completely baseless as you fail to provide any valid reasons why there would be a correlation between the two besides a misinterpretation of the evidence. We have to assume that the mother's genetics play no role in passing on the the carrier gene and a gene linked to only the father cannot be only sex chromosomes (remember I said only). I know this may sound slightly abbrasive but if you'd like to discuss this or hear more about my explanation, leave me a message or check my blog here soon as I will soon be adding a new entry dedicated to constructing a valid explanation for the carrier heritage. We are in agreement about one thing though: "Either the special infected thing is decided by a myriad of genetic or environmental factors, or it's got no canonical explanation and is just a simple gameplay element. I'll make a variation of your diagram and see how you feel about it" Shawty71 18:37, October 4, 2010 (UTC)

All I'm saying is, it seems more likely to me that Valve would make the immunity situation comparable with a real-life mechanism that people might be familiar with rather than some esoteric combination of genes that is more akin to a science fiction device aimed at a specialised audience. I'm not saying immunity has anything to do with color blindness, just that immunity is passed on in a similar way. A person with only rudimentary knowledge of heritation might interpret "Runs on the father's side" as being a trait commonly suffered by men, such as color blindness, the reason being that it's X-linked.

"So maybe Valve isn't medical experts, or are they? How do you know?" They're video game developers. They know what rabies does, they know what a virus is, and even got a carrier plot going, but I highly doubt that they are knowledgeable on heriditary genetics, let alone so in-depth that they designed themselves a fictitious genetic situation. Because I don't know of any natural occurences where autosomes are linked to one particular sex, or where a father's X-chromosome is somehow capable of passing on genes where the mother's isn't. Left 4 Dead may not have a realistic premise (zombie apocalypse), but it does aim to have a realistic setting, and so far every location and story element (aside from the infection) is compatible with, if not based on, the real world.

The way I see it, the doctor's statement was meant clue the reader in on the method of inheritance of the gene, followed by Zoey's flash back and the tragic realisation that she killed her father for nothing, due to what she'd just learned. And that's the end of that. If no more evidence surfaces on this issue, will you give my theory the benefit of the doubt? I know it's based on intuition rather than evidence, but the doc's statement is open for multiple interpretations and doesn't plainly state what you say it does, either. In fact, if you interpret it in the most literal way possible, you'd conclude that only men can inherit and pass on the gene, which is obviously not the case. Monojin 22:15, October 4, 2010 (UTC)

"Carrier VS. Immunity"
Looks like that article section proposes immunity as a state where your immune system destroys the infection, and it's ALL bullshit. You can't form antigens against something that mutates daily. That was a hint dropped specifically to debunk these hopeful theories.

I have a post with what I consider a complete picture of the thing here. I realize that there are a lot of people enthusiastic about bad plot points so they can have their 100% happy ending, but you're entirely missing the point if you hold on to the possibility that the survivors may not, in fact, be carriers.

Just look at the radio convo between the survivors and the rescue team at the end of The Parish. The pilot learns that they've come across the infection and deduces that they must be carriers. There is no option for these mystical people who have superhuman immune systems and will likely never get sick from anything (except HIV).


 * Okay, I've edited the article since no-one responded. To illustrate what I mean by innate immunity, see this schematic. What Valve probably means is Immunity > Innate Immunity, and what everybody hopes is the case is Immunity > Adaptive Immunity > Natural > Active (Infection), which is impossible due to the virus mutating daily. If anyone minds, please read my SPUF thread and reply there with valid counterpoints. Monojin 12:35, October 3, 2010 (UTC)
 * I actually commented on deleting this section of thee article earlier in the page too (you probably didn't notice it becuase I could make a new heading). I agree with you 100% of the way, although I simply stated that the doctor made no mention of any true immunity. If it does make you feel better, the user who created the section (shawty) also believes it should be deleted do to it being misleading.Whachamacallit 23:52, October 4, 2010 (UTC)