Oh, I don’t think it begins as female, just heading towards female. That’s what I was taught in my most recent course and I didn’t think much of the teacher, so I won’t be surprised if it is wrong.
To help fight my own ignorance, here is what I was taught, please tell me what part of this is wrong and what is correct:
Since there are some species which exist composed of only females, it brings up the problem of why males exist at all if a species of females can survive on its own. Well, as it turns out, sexual reproduction is more benefitial to the species than asexual reproduction because of the variety of genotypes. The species starts out as all female and then one female produces a modified female, who produce, instead of eggs, mobile offspring (sperm) so that they can mate with other females and produce hybrid offspring. This is why the Y chromosome is less genetically healthy than the X chromosome.
Thanks.
Sampiro wasn’t talking about AIS, as far as I can tell, so I wasn’t talking about AIS when I responded. AFAIK, AIS-XX women are normal women.
The idea that there are species that are all female seems bizarre to me. I don’t even understand what that could mean - there are species without sexual differentiation, sure. But that means they’re not female, I’d say. Again, it’s semantics, but I don’t see how you can characterize a species without sex as belonging to a sex.
It’s not really the case that it’s “heading towards female”, either. The hormones produced are largely the result of which gonads are present (or absent, as the case may be). Since gonadal development is under genetic control, then subsequent genetic development is, ultimately, under genetic control, as well. In some cases, development does proceed diffrently, of course, and we get into cases of individuals who are genetically one sex, but who develop sexual characteristics of the opposite sex. But, if things proceed “as planned”, for lack of a better term, then the goands are produced based on genetics, and those gonads begin producing hormones which regulate further development (at least in the case of males; MIS and testosterone are both produced by the testes, so once those form, the rest will theoretically fall into place).
Again, the simplest description is that a fetus is initially sexually undifferentiated, then develops into one sex or the other based on certain genetic / hormonal parameters.
I don’t know of any species which are composed solely of females. There are species in which development does default along female lines, unless there is a good reason to create males (e.g., aphids; such species generally also have the means to reproduce via parthenogenesis, and many such species typically do not possess sex chromosomes at all - rendering the entire concept of “what sex is it?” somewhat irrelevant), and there are species in which various environmental parameters can control the resulting sex (e.g., some amphibians and reptiles, wherein the resulting sex can be controlled by the ambient temperature).
Then what are you talking about? Do you have a name for this condition, with the region on the Y-chromosome getting switched over (to what? The X-chromosome?)?
There is a species of lizards in the America Southwest which is entirely composed of females. My teacher apparently studied them for his dissertation so I assumed that he knew what he was talking about when he said that the default is female and male is a mutation that occured in the course of evolution. His definition of female was screwy too, I now see. He said that females were creatures that could reproduce and males do not have the ability to reproduce but just aid females in reproduction. That’s wrong too, I bet.
Sofis, I do not think the condition has a name, it is normally the result of mocaism. For example, there were a male and female twin who were mosaic and the male twin had 30% XY and 70% XX. The female twin had 22% XY and 78% XX. The region of the Y chromosome, which is known as (sex-determining region Y) was present in the male but not the female.
Since they say that female is the ‘default’ program, I assumed that the fetus were heading towards female development and it was the interaction of the SRY which made the fetus become male instead.
So would I. According to this paper (.pdf document),
From the sound of things, only a few species have actually been karyotyped, and at least some of those species which are unisex have no sex chromosomes. Thus, the “female” label seems to be pretty arbitrary. Plus, the fact that there are apparently species with “male heterogamety” kind of throws a wrench in the supposition that males are unable to reproduce.
It lacking a name seems very unlikly; scientists are a very naming-happy bunch, and if they encounter a condition even slightly out of the ordinary, they tend to name it, often in Latin. Sometimes it’s named more than once.
Wait… you’re talking about a pair of fertilized eggs, one XX and one XY, that merged, mixing their cells… and then split again, into two separate embryos, both being a mix of XY and XX cells… but one of them developed into a female, because the sex-determining regions on her Y-chromosomes had all been… moved elsewhere? Or are you talking about four separate fertilized eggs that paired up and merged? Or something else entirely?
I don’t think I understand your example.
The thing about how you’re describing it is that you make it sound as if early fetal development is a very female affair that does its female thing and is very, very female and suddenly it grinds to a screeching halt, turns around, and heads off in the opposite direction, doing stuff that has nothing to do with the all-female things that went before.
It’s a branching point. First comes stuff that is common to both sexes, then there’s differentiation depending on a certain factor. Now, sure, that factor is the presence or absence of a set of genes on the Y-chromosome, but that doesn’t mean it’s meaningful to count the early development as being female. It lends itself as well to male development as it does to female development.
Well, if you can find a name, let me know. I find this type of stuff fascinating!
Unfortunately, I returned the book which contained details of this particular case to the library and I can’t find the case online, so I don’t know exactly how that cases ended up the way it did. :smack: I do know that there were two fertilized eggs, but they never merged together, they just shared a lot of genetic material.
But I can give you information about other cases involving mosaics. This site explains how :
Yeah, I didn’t mean that at all, I was trying to explain the branching but not doing a very good job. I’m horrible at getting across what I am trying to say in english. That’s why I said I needed to draw a diagram because then you would understand what I am trying to say. I said ‘on the way to female development’ instead of ‘female’ because I wasn’t sure the correct technology to use to describe the branching off. So basically, I think we were in agreement the whole time.
Actually if I recall correctly ( all of my Cnemidophorus/Aspidoscelis stuff is at home, so I can’t immediately check it - it’s also mostly at least a decade out of date ) most, or at least many of the North American Cnemidophorus have been karyotyped and they’re rather more diverse than there congeners in South America. The American Southwest/Northern Mexico is ground central for the genus, as it is for a few others reptiles like Crotalus.
No it’s pretty standard terminology for parthenogenetic/unisexual whiptails. They all arose instantaneously through interspecific hybridization events and in addition to being parthenogentic they appear capable of further back-crossing with bisexual species to form triploid parthenogens - hence the origin ( probably multiple and of possibly different source species ) of lineages like Asipidoscelis exsanguis or A. velox.
I stand corrected then. Thanks for the info, Tamerlane.
I don’t think that changes the overall points about a) females and males, regardless of species, differentiate from a common developmental progenitor, rather than development proceeding along one line and changing under whatever circumstances, and 2) males aren’t “mutations” based on a female body plan.
