AWKWARD ZOMBIE

Of course that would have the exact opposite effect to what you wish for.

Dying of drowning/blood poison/eaten by sharks was easily preferable to being that thirsty

I think D-Vid meant more that salt water wouldn't satisfy your thirst at all.

Also it will kill you eventually.

Not to mention diarrhoea and vomiting.

Diarrhea and vomiting eventually leading to death.

I used to take ritalin, but it was for sluggishness.

Shitting yourself to death via dehydration.

Not a fun way to die.

Just ask the millions who have played Oregon Trail.

So I've had a question on my mind for a while, and my biology teacher is sort of flipping out about our state assessments (I'm in high school) so he asks for question and then ignores any hands that go up. Sort of frustrating, they make state tests easier than they should be anyway.

But I digress, my question is about Meiosis. Meiosis is where chromosomes cross over and swap segments to increase genetic diversity, yeah? (just checking to make sure I'm not remembering wrong) So is there some sort of process or something that keeps the sex chromosome from crossing over and swapping their important bits? Especially given that they're different sizes and it would really cause issues if a guy got a chromosome that was half-x-half-y and a y, since y doesn't have enough genetic information to grow a human (in the hypothetical scenario where an organism gets two y chromosomes, of course.)
I'm certainly not trying to point out some place where science is wrong or anything like that (as so many people seem to do), since it's pretty evident that the cross over doesn't happen; I'm just curious about this and my teacher sort of sucks.

Another question is how the number of chromosomes in different species can be different. For example, apes have 24 pairs while humans have 23. I've been informed that only plants can change the number of chromosomes between offspring, and even then they can only double it.
Is the variation in chromosome quantity simply due to really freakish mutations that made a lot of organisms suddenly lose a pair of chromosomes all at the same time (since an organism can't breed with an organism with a different number of chromosome)? This seems really improbable.

I'll start with the meiosis one and answer the chromosome one tomorrow, since I happen to have genetics class then.

I think the cross over does happen, since an Y-chromosome is just an X with a bit chopped off. So when they cross over, the usual just occurs with the parts that match, and where the Y-chromosome is different it doesn't have anything at all so cross over can't occur. In the case that I'm wrong and Y-chromosome does have genes that are incompatible with X and vice versa, there would be only a few and the chance of a cross over messing with those would be small. If it did happen you'd be screwed of course, but shit happens.


Edit: DISREGARD THAT I SUCK COCKS.

Man, it's amazing how a shower makes you think clearly. I'm giving up on explaining myself though and just linking to the relevant wikipedia article. An interesting thing of note however, is that the sex chromosomes might still get messed up through chromosomal translocation, which can change around the SRY-gene, leading to odd stuff.

This is an interesting question which I haven't actually addressed in my own understanding of DNA.

The default answer in any question like this relating to genetics - is as usual - random and/or accidental mutation:


Source page.


I find it particularly interesting how - in the middle paragraph - it is explained that all the different genes relating to the eye have arisen from the replications and mutations of a single gene.

I find genetics incredibly fascinating; The parallels with computer programming are just... fascinating.

The problem that arises with that standard answer in this case is that the probability is too low. If an extra chromosome pair were to appear as Ycobb said, then you're unable to breed with other things. It would only be possible if an other creature would have the same mutation at the the same time.

The mistake you make Ycobb, is progressing too fast. I think it would be more logical if an extra pair of chromosomes would start very small and accumulate or deteriorate over time. That way, the mutation might still be able to pass when breeding with a non-mutated specimen. For example, the current deterioration of the Y-chromosome. If using a linear extrapolation, that chromosome might completely lose function within the next 10 million years. Or not, see link. I could ask my professor about this on Friday if you still have doubts, this is just an explanation me and my classmates came up with.



I agree, I'm thinking about specialising in genetics actually ^^.

It's not an entirely pleasant thought but I would argue that it occurs when organisms of close relation interbreed (brother x sister, father x daughter, mother x son, etc); that way a new pair of chromosomes would be more likely to become established.

This interbreeding within a tight-knit family group is also more likely to occur in isolation - say if they were deserted on an island away from any other breeding partners of their own species (isolation being a key driving force in evolutionary divergence).

I don't think interbreeding can trigger something as drastic as adding another chromosome.

Inbreeding is bad because every creature carries a bunch of recessive genes that can cause malfunctions and diseases. If they breed with creatures with similar genes(relatives) this increases the likelihood they get more copies of the same recessive genes (become homozygote for that gene) and thus those recessive genes can be expressed and cause shit.


Addendum:


Absolutely true, but in general a large enough portion of the population should be isolated to optimise the chance of successful divergence. The two isolated groups of the same species should also be subject to different environmental conditions so that they can select for different traits through natural selection. The isolation is to prevent these different traits from blending in to one form again.