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Comment Re:Trade off (Score 1) 106

Environmentally-induced mutation definitely does play a large role in tumor formation--that's why smoker's get lung cancer, sunburns can lead to skin cancer, etc! There's also viruses that can play a role.

However, we also don't really know how many mutations are necessary for cancer to arise, and one of the first things to happen may be either immortalization through mechanisms including telomerase activity (or the tumor could arise in stem cells where this activity is already present) or (more often) a mutation that in turns leads to an increased mutation rate! Regardless, it's probably not that many mutations, and don't underestimate just how large a number of cells there are in the body (on the order of 10^13 - 10^14)!

Comment Re:Trade off (Score 3, Informative) 106

In humans, telomeres limit cells to ~50 divisions, which is probably related to how DNA replication is only 99.9998% accurate. After that many divisions, the genome is 0.001% different from when it started, which is one error per 10,000 base pairs, or an error in 1/3 of all genes. This is in addition to the slow rate of spontaneous mutations you accumulate over your lifetime.

Where did you get your numbers? Human DNA replication (in normal cells with no damage) is 99.99999999% accurate (i.e. about 1 mutation per 10^-10 base pairs). Please do not mod parent informative for this misinformative post!

Comment Re:Topical sites cause traditional search to shrin (Score 1) 184

Sure...but on the other hand, as soon as you start typing "Gy" into imdb, Gyllenhaal comes up complete with a photo and a big-name movie (for both Jake and Maggie). And if you type in secretary, it brings up an option to go straight to the movie page--without even having to type Gyllenhaal too. So I'd say that's quite a win for imdb. You don't need to know who is in the movie, you don't need to be able to spell "Gyllenhaal"....

Comment Re:names egregious, but not relevant (Score 3, Informative) 268

To clarify, you want each of your markers to carry maximum information. SNPs are the easiest/cheapest markers to genotype, and represent positions in the genome where some chromosomes in the population have one nucleotide (e.g. G, one of the alleles) and others have a different nucleotide (e.g. T, the other allele). (I say chromosomes instead of people, since people are diploid and will have 2 copies of each chromosome. Diploid genotypes are then GG, GT, or TT for a G/T SNP). To maximize information, you want to choose a SNP where the probability of these genotypes is relatively even--maximized if the proportion of G's and T's in the population are equal, leading to 25% GG, 50% GT, and 25% TT.

While the parent is correct that 24 SNPs is sufficient in a given population, in practice it's probably hard to choose 24 SNPs that cover ALL populations in the world well (since a SNP with a high minor allele frequency in, say, Europeans, may not have a high minor allele frequency in Asians, or Indians, or Australians...

The Perfect Way To Slice a Pizza 282

iamapizza writes "New Scientist reports on the quest of two math boffins for the perfect way to slice a pizza. It's an interesting and in-depth article; 'The problem that bothered them was this. Suppose the harried waiter cuts the pizza off-center, but with all the edge-to-edge cuts crossing at a single point, and with the same angle between adjacent cuts. The off-center cuts mean the slices will not all be the same size, so if two people take turns to take neighboring slices, will they get equal shares by the time they have gone right round the pizza — and if not, who will get more?' This is useful, of course, if you're familiar with the concept of 'sharing' a pizza."

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