Genetics/Sex question

[EternalFrustration]

Hi everyone, any biology/genetics gurus out there? I'm trying to flesh out a concept and I'm wondering if it's actually workable. Can you help?
My idea is this: a con-species with 4 genders. An individual of one gender can mate and reproduce with an individual of any of the other 3 genders, and the offspring would have a 50/50 chance of being the gender of either parent.
It's been a long time since I last did Punnett squares in my high school bio class. Is something like that feasible?
Thanks for your help.
P

(Edited to add: To be clear, I know this is not original, so when I say "My idea" I mean the term very loosely)

[2+3 clusivity]

Well, to make an analogy, if now we have XX and XY . . . . then, I guess if XY and YX were somewhere different and YY was viable this would work? Making all results viable to reproduce seems difficult. It might be more interesting to have just XX and XY viable or maybe XX, XY and YX.

Still in the longterm it would seem that doubling the amount of genders would put the longterm survival of a population at risk. Imagine if we worry about the lack of men/women in certain small populations, just image the same fear when you have to balance the population of four sexs!

[Torco]

no, no, you've got it backwards, clusivity, having a bunch of interchangeable genders actually makes reproduction easier: like i can reproduce with one half of the population so if i encounter only two people in my life there's a 25% chance I won't be able to even try to reproduce; if there's 4 genders that can all reproduce with each other [that is, the only requirement to reproduce is that you don't fuck your own gender] then 75% of the population is elegible for reproduction with for each individual. The problem here is that the gender of the offspring is determined by the gender of the parents: given any sort of sexual differentiation of phenotype [like with us humans, which have bigger males that can reproduce for longer <typical women stop being fertile at like 40-50, males not so> or with hyenas, which have bigger more dominant females] you'll end up having differentiated fitness for genders [say, if gender 4 is bigger they'll die more often during times of hunger, or if gender 2 is smarter they'll survive more readily when things change, or whatever]. This will make the whole system unstable, since it would mean that any one gender might be liable to die off [if gender 2 dies more than the other genders, next gen will have less gender 2 so the proportion of gender2 individuals in the third gen will be even smaller, which would make in turn the proportion of gender 2 in gen4 smaller, and then smaller in gen5, until there's no gender2 in genX].

In contrast, if offspring sex is orthogonal to parent sex, the foursex system is stable.

[EternalFrustration]

no, no, you've got it backwards, clusivity, having a bunch of interchangeable genders actually makes reproduction easier: like i can reproduce with one half of the population so if i encounter only two people in my life there's a 25% chance I won't be able to even try to reproduce; if there's 4 genders that can all reproduce with each other [that is, the only requirement to reproduce is that you don't fuck your own gender] then 75% of the population is elegible for reproduction with for each individual. The problem here is that the gender of the offspring is determined by the gender of the parents: given any sort of sexual differentiation of phenotype [like with us humans, which have bigger males that can reproduce for longer <typical women stop being fertile at like 40-50, males not so> or with hyenas, which have bigger more dominant females] you'll end up having differentiated fitness for genders [say, if gender 4 is bigger they'll die more often during times of hunger, or if gender 2 is smarter they'll survive more readily when things change, or whatever]. This will make the whole system unstable, since it would mean that any one gender might be liable to die off [if gender 2 dies more than the other genders, next gen will have less gender 2 so the proportion of gender2 individuals in the third gen will be even smaller, which would make in turn the proportion of gender 2 in gen4 smaller, and then smaller in gen5, until there's no gender2 in genX].

In contrast, if offspring sex is orthogonal to parent sex, the foursex system is stable.

Do you mean: Parent1 is gender A, Parent2 is gender B, offspring will be either gender C or D?

[Neon Fox]

In contrast, if offspring sex is orthogonal to parent sex, the foursex system is stable.

Do you mean: Parent1 is gender A, Parent2 is gender B, offspring will be either gender C or D?

No, Torque means that the sexes of the parents do not influence the sexes of the offspring. Parent1 is A, Parent2 is B, but offspring can be any of A, B, C, or D.

[Torco]

Neon read it right, but I guess the alternating thing would yield a stable system as well?

[EternalFrustration]

Neon read it right, but I guess the alternating thing would yield a stable system as well?

Okay, so then how would the gender of the offspring be determined? Is there something like a Punnett square that would show how that works out? Because I can't quite wrap my head around how to get it to work.

[Basilius]

Supposing the sexes are genetically determined, "stability" means that the progeny of each individual will ultimately include all the sexes.

Ideally, this must be achieved without involvement of any genetic markers which that individual and that individual's mate don't have together.

Non-ideally, the same goal can be achieved by forcing all the progeny of that individual in one of the subsequent generations to mate with individuals of yet another sex (or several other sexes) who have the missing markers.

The latter seems impossible, and the former rather sophisticated under the condition that each individual can mate with all sexes other than that individual's own.

A couple examples to illustrate this point.

(1) A stable system of three sexes, with two genetic markers, "A" and "a" (these aren't necessarily alleles, we can have different chromosome sets or something).

"AA" can mate only with "aa" (and vice versa), their progeny are 100% "Aa".

"Aa" can mate only among themselves (or are self-inseminating); their progeny are 50% "Aa", 25% "AA" and 25% "aa".

The system is stable, for the progeny of each mating pair (and/or each individual) can ultimately include all the three sexes.

(2) Same as above, but with mating of "AA" with "Aa" and "aa" with "Aa" permitted, and mating among "Aa" forbidden (to comply with the condition about free non-same-sex mating).

"AA" mating with "aa" produce 100% "Aa", which need to find either "AA" or "aa" to have any progeny, on which see below.
"AA" mating with "Aa" produce 50% "AA" and 50% "Aa"; these can mate among themselves, and "aa" may never appear in this lineage.
"aa" mating with "Aa" produce 50% "aa" and 50% "Aa"; "AA" may never appear.

The system is unstable.

[Cedh]

Assume three different sexes A B C, which are determined by the interplay of three genetic markers, also A B C. These markers interact with each other as follows: A is dominant relative to B; B is dominant relative to C; and C is dominant relative to A. Someone of phenotype A can be AA or AB genetically, someone of phenotype B can be BB or BC genetically, and someone of phenotype C can be CC or CA genetically. Each phenotype can mate with both of the other sexes, but not with itself.

For a couple of sexes A+B, chances for a particular type of offspring are 56.25% for A(AB), 18.75% each for B(BB) and C(CA), and 6.25% for B(BC). These can produce all sexes, and indeed all possible genotypes, by mating among themselves. Of course, the odds for a particular genotype are rather skewed.

For a couple of sexes A+C, chances for a particular type of offspring are 56.25% for C(CA), 18.75% each for A(AA) and B(BC), and 6.25% for A(AB). Again, these can produce all possible genotypes by mating among themselves.

For a couple of sexes B+C, chances for a particular type of offspring are 56.25% for B(BC), 18.75% each for C(CC) and A(AB), and 6.25% for C(CA). Again, these can produce all possible genotypes by mating among themselves.

If you start with two individuals of each gender, forming three couples, one of each of the above types, the overall chances are 27,08% each for the mixed genotypes A(AB), B(BC) and C(CA), and 6,25% each for the pure genotypes A(AA), B(BB) and C(CC). Since the latter three genotypes all require at least one of the parents to be of a mixed type, their probability should be slightly higher in the next generation IIANM, balancing out the genotypes even better. The system is stable.

Such a system would presumably also work with four markers instead of three, giving something quite like what the OP asked for.

[Kereb]

I remember hearing recently about some kind of microbe that has seven sexes, any two of which can produce offspring, and the offspring can be any of the seven sexes no matter what the parents were.

EDIT: Bam. Some general but not too specific information on how this works ... a place to start i guess

[Basilius]

However, a couple whose genotypes are AA and BB may never have any progeny of the C gender, or am I missing something?

This means that some subpopulations can have a degraded sex system (without loss of fertility), and that sex ratio can unpredictably drift towards the extinction of one gender.

I'd call this unstable.

[Basilius]

Kereb:

Tetrahymena are rare among single-celled organisms in having two nuclei. The germline nucleus, like testes and ovaries in humans, contains the genetic information that will be passed on to offspring. The somatic nucleus holds the ‘working copy’ of the organism’s genome, which governs the cell’s behaviour and determines its mating type.
'You complete me'

Every Tetrahymena cell in the study had the same genome in its germline nucleus. That genome, the researchers discovered, contains incomplete genes that correspond to mating types. When two organisms mate, the combined fragments contain all the information necessary to encode any of the seven mating types in their offspring. This DNA is then delivered to the newly formed somatic nucleus of the offspring. The DNA is then rearranged and parts of it are deleted through a random process until there is only enough information to express one mating type.

This isn't what I'd call a "genetically determined" system, but it works.

[Kereb]

yeah I don't know what you would call it. The genes are always there, but it's maybe epigenetically determined? Or maybe completely random? As a conworld concept though one could decide to have it either way.

[Basilius]

yeah I don't know what you would call it. The genes are always there, but it's maybe epigenetically determined? Or maybe completely random? As a conworld concept though one could decide to have it either way.

If I understood it correctly: basically, you have two copies of genome; one is copied to your progeny, the other is randomly modified and determines your phenotypic sex.

In a multicellular organism, you wouldn't even need two nuclei per cell to implement a similar mechanics.

I wonder why it is like it is; in terms of gene recombination, it's not different enough from a single hermaphrodite sex, and yet it involves a sophisticated machinery to make the phenotypic sex random...

It can be all about just excluding mating among clones, which would be not plausible with organisms that only multiply via mating.

[Salmoneus]

In considering stability, you also have to consider mutations.

If Sex A is fitter than Sex B, then regardless of the details of the sex determination system, individuals of all sexes will be more genetically succesful if they have mutations to be more likely to have A offspring than B offspring. So having multiple interchangeable sexes seems inherently unstable, unless there's some actual reason for it.

What's the actual reason for this system?

[2+3 clusivity]

no, no, you've got it backwards, clusivity

Clearly I need to brush up on my . . . uh . . . ConBiology?

[brandrinn]

Even without any differences in fitness, a 4 sex system will eventually reduce, given enough time. At least, so long as the children's sex is determined by their parents. The same happens with any lineage. Patronymic names break down over just a few thousand years (compare the Netherlands to Korea). So you would need no significant sexual dimorphism, no hidden potential for gaps in genetic fitness, and random sex determination at birth, all of which probably takes away the fun of having 4 sexes in the first place. Just give them 2 sexes and throw in some racial and social monkeywrenches to make it more interesting.

[Kereb]

I think the deal with the microbes is probably that they're so identical that there aren't sexual differences that might contribute to fitness. You could argue that all mutations could potentially cause such a difference but if it's too subtle to be selected out, that's why the system persists. I remember reading about a fungus that had thousands of "sexes" but that's probably again just a reproduction compatibility hiccup between variants that are otherwise pretty much identical.

BUT then as far as conworlding goes, you'd probably want your different sexes to be different from one another otherwise it's not interesting enough to write about. The system might reduce "given enough time" ... but you can handwave that and just suppose the meat of your conculturing takes place at a stage where it hasn't reduced away yet. Star Trek got away with it -- there were at least a couple of species mentioned who had multiple sexes.

[Basilius]

Brandrinn: however, our human system hasn't degraded to one hermaphrodite sex, "given enough time".

Nevertheless, empirically you (and Salmoneus) are right.

Systems of multiple sexes with little differentiation are mostly found among single-celled organisms and fungi, where they coexist with asexual reproduction (therefore, their main purpose may be to restrict mating among clones).

In multicellular animals, systems of exactly and precisely two sexes dominate.

Sure, there are other options, including hermaphroditism, parthenogenesis, sex switched with age, sex switched by the presence of mostly same-sex specimens, alternation of generations with sexual and asexual reproduction, etc. etc. All of them can be stable even "given enough time", that is, at least within the history of whole species. However, all those more exotic sex systems are marginal e. g. among vertebrates.

A problem here is that despite tons of literature on the topic, there is no short and universally accepted answer (AFAIK) to the question why systems of two genetically determined sexes are so prevalent, especially among higher animals. (In particular, the specific genetic mechanisms which determine an individual's sex are rather varied, which means that it's not just rigidity of genetics that secures stability in this point, there's probably some powerful advantage in the system itself.)

But this also means that one can't point to a simple mechanism supporting such systems and claim that due to a set of plausible reasons it doesn't work for one's conspecies, while a different plausible mechanism of related nature supports a different set of sexes as equally stable.

In other words, multiple sexes in a sentient conspecies cannot be based but on a handwaving. So it looks.

[Torco]

The two sexes thing looks like it would be the path of least resistence, so to speak: it cannot grow less complex because you'd loose sexual reproduction [actually it can, there are all-female lizards that all have virgin births, they're all called Mary of course, but likely the'll be outcompeted rather quickly in evolutionary terms] and it gives exactly the same benefits as a three way system would: many-sex systems only look like they would work better than two-sex ones in contexts where individuals would encounter very few of the species in their lifetimes; in that case, having four sexes triple the chances per encounter of finding a viable mate. Hermaphroditism, however, solves that problem much more elegantly.

But evolution isn't about elegance or about finding the best solution: consider we have a *respiratory invagination* for crying out loud, and just look at the knee for an example of retarded design. we humans have chokey throats and we have outer gonads for crying out loud... outer gonads. The organs that actually perform the prerrequisites for reproduction [making sperm] are not safely tucked inside the body, they're in a flappy bag of skin just below the arse!

So the two sex system works and that's why it works, but its probably due as much to chance and blind mutation as it is to the fact that it functions: if the common ancestor of all eukariots had been different, possibly we'd all be hermaphrodites, or maybe something funkier [like when two organisms have sex the two organisms get pregnant].

[Basilius]

So the two sex system works and that's why it works, but its probably due as much to chance and blind mutation as it is to the fact that it functions: if the common ancestor of all eukariots had been different, possibly we'd all be hermaphrodites, or maybe something funkier [like when two organisms have sex the two organisms get pregnant].

Well, no. The problem is that it's nothing like having the same set of aminoacids or anything of that sort. As I said, specific genetics behind the two sexes is enormously diverse. It looks like it has been broken and redesigned a thousand of times. But it also looks like it was mostly allowed to collapse only in such ways which permitted a rebuilding of the system of two sexes, and specifically "male" and "female".

The advantages of sexual reproduction per se are more-less obvious (recombination), the enigmatic bit is why humans (and most vertebrates, and most insects, etc.) aren't hermaphrodites or something.

[Torco]

Well sure but that might well be due to the specific way in which our genetic molecule, or recombination mechanism, or something, happens. which unless there's a god this

But it also looks like it was mostly allowed to collapse only in such ways which permitted a rebuilding of the system of two sexes, and specifically "male" and "female".

quite clearly suggests

I understand the specifics of what male and female mean are kinda blurry beyond vertebrates... and definitely blurry outside animals. Furthermore, its quite possible that sex evolved just once, since all sexual things now share a common eukariotic ancestor, and most eukarions seem to be sexual or have been, like the Mary lizards... and a lot of this happens more or less in the same way; ova and sperm [as opposed to, i don't know, an organ that takes the tissue from another organism and takes genetic material from there, which is in principle no crazier than the sperm-ova thing]

[Burke]

Well sure but that might well be due to the specific way in which our genetic molecule, or recombination mechanism, or something, happens. which unless there's a god this

But it also looks like it was mostly allowed to collapse only in such ways which permitted a rebuilding of the system of two sexes, and specifically "male" and "female".

quite clearly suggests

I understand the specifics of what male and female mean are kinda blurry beyond vertebrates... and definitely blurry outside animals. Furthermore, its quite possible that sex evolved just once, since all sexual things now share a common eukariotic ancestor, and most eukarions seem to be sexual or have been, like the Mary lizards... and a lot of this happens more or less in the same way; ova and sperm [as opposed to, i don't know, an organ that takes the tissue from another organism and takes genetic material from there, which is in principle no crazier than the sperm-ova thing]

I've had an off day, so don't hound me if I'm off, but I believe that I have read that, much like the development of eyes, sexual reproduction is a case of convergent evolution. As you mentioned earlier, it is an effective means for producing strong offspring. And strong offspring are more likely to be able to reproduce, given normal situations.

[Basilius]

Well sure but that might well be due to the specific way in which our genetic molecule, or recombination mechanism, or something, happens.

All such things are also present in hermaphrodites etc.

<...> unless there's a god <...>

I wouldn't mind, but I didn't mean that.

Actually, it's not too difficult to invent a quick-and-dirty explanation. Like, with males and females you can kill almost one half of the population without really affecting its reproductive potential - and yet your gene pool will receive the signal about what is needed to survive in the presence of the new lethal factor.

However, such explanations aren't universal, there are objections, and objections to objections, and objections to objections to objections, and people who say they know why it's like it is tend to look like a sect or clique rather than careful scientists who can hear criticism. Also, no such explanation explains why (e. g.) females aren't hermaphrodites (capable of mating with both males and their own sex) &like.

<...> a lot of this happens more or less in the same way; ova and sperm [as opposed to, i don't know, an organ that takes the tissue from another organism and takes genetic material from there, which is in principle no crazier than the sperm-ova thing]

Sure, there could be something totally different. But ovum plus sperm is what hermaphrodites have too, and a number of other alternative systems have or could have as well.

[Torco]

It doesn't look convergent to me: all eukarions [well not *all*] have sex, all eukariont [is that the adjective?] sex is pretty similar [i think, I'm no expert]. Furthermore while there is a lot of horizontal gene transfer going on [and the various mechanisms for it certainly seem divergent]. that looks to me like the common ancestor of eukarions was probably the guy who started doing the whole sex thing.

Sure, there could be something totally different. But ovum plus sperm is what hermaphrodites have too, and a number of other alternative systems have or could have as well.

Yeah, totally.... eukarion hermaprhodites look like sexual organisms that went ahead and went hermaphrodite after, not things that went from asexual to hermaphrodite.