C-Talos

Hello, In Wasserman & Faust's "Social Network Analysis" I read about the following problem with the n-clique concept: They give some references (Alba & Moore 1978, Mokken 1979) which I can't access. I've been drawing lots of graphs to find an example of the above but can't find any. Anyone knows? Thanks! For those not in the know: a geodesic is the shortest path between two nodes; an n-clique is "a maximal subgraph in which the largest geodesic distance between any two nodes is no greater than n".

to SkepticLance: But in the alternative pathway involving unknown factor F, X&Y-chromosomes would still precede sex development - the difference is that they themselves would be preceded and modified by the (largely invisible - perhaps it sits on an autosome) factor F. This alternative still agrees with the known timing which you mention. I suppose no one has ever noticed an X from a gamete turning into an Y after fertilization, or the other way around, so there's certainly a lack of positive evidence for such a pathway... But if I understand Eric Lander's lecture there was indeed an issue, and I'm trying to understand this issue and how the sex-linked genes provided a resolution. thanks again both!

Thanks for your thoughts people! Mr Skeptic, you are right, he would have to make that assumption. This 'unknown sex-determining factor F' would have to modify a Y into an X if female, and an X into a Y if male. As Paralith notes, this would involve more than 'chewing off' bits or 'pasting them on'. This scenario may seem far-fetched or inefficient, but not therefore impossible? So let's assume that these geneticists around 1910 were thinking that might be the case. Then I still don't see how this business of sex-linked genes such as white in Drosophila would have convinced them that it is not the case. Perhaps I'm not clearly understanding how much information geneticists had back then. I'm assuming they could clearly observe chromosomes in somatic cells and gametes. A bit of observation should then have suggested the actual "X/Y chromosomes determine sex" hypothesis as a likely one, but still leaving the more convoluted one as an option...? BTW, pioneer, I'm a bit skeptical about your 'female chromosome is larger because female reproduction is more complicated' theory. Even if, in line with your theory, it is also the more bulky chromosomal package that says 'female' in the sex determination system in birds. But check this page: "The X chromosome carries hundreds of genes but few, if any, of these have anything to do directly with sex."

Hi folks, In a cool MIT lecture (Genetics 2), Eric Lander says the following (quote from the transcription): Good question. He then goes on to describe the Morgan lab results about eye colour being linked to sex. Then he says: I don't quite get this. It's still just a correlation, right? If you asked before "hey perhaps sex (caused by some unknown factor F) affects the chromosomes after fertilization?" then you can now ask "hey perhaps factor F affects the chromosomes AND consequently the eyecolour they determine, after fertilization?". I'm obviously not really disputing the chromosome->trait causality. This is about the historical methodology issue that Lander raises; and I don't quite get the answer. Is it ultimately just a question of not finding good candidates for this hypothetical factor F, whereas the chromosome as the causal agent seems very plausible? In other words: a probability and parsimony-of-explanation argument rather than a logical proof? Any insights? Thanks!