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Matthew - your figure of 2^23...that would be correct if chromosomes were either or choices. But they are not each chromosome varies internally to a greater or lesser extent.

Quote from: imatfaal on 12/01/2011 14:34:33Matthew - your figure of 2^23...that would be correct if chromosomes were either or choices. But they are not each chromosome varies internally to a greater or lesser extent. Why aren't chromosomes an either or choice, is that just crossing over? I understand now, due to the high amount of crossing over that the chances of this happening are very very slim. BUT (regarding the quote)Surely during meiosis the homologous chromosomes (2 chromosomes) line up, they are then split (after crossing over). so surely that is a 2²³ combinations (excluding crossing over). each chromosome can either be in half 1 or 2, and there are 23, which ≈ 8 million.

Have you factored in alleles into it?

Quote from: Variola on 12/01/2011 19:59:18Have you factored in alleles into it? Alleles are just an essences of the genetic code. What it codes for. Its all contained on the chromosomes, so yes.

thats the rough number of combinations any two parents can have - ie you get half as a selection from your fathers and half as a selection from your mothers. But my mother and your mother have different selections to choose from - although they did both call their sons Matthew!

Errr not entirely no. If you are calculating the odds of identical genomes occurring then alleles feature heavily into that. They are not just simply an essence. And then you have to consider SNPs...... I am no maths guru, but I would guess the calculations are impossible to do.

Ok...I think your numbers are off. Here is how I'm calculating it.If you have 23 pairs of chromosomes... from the father... of which you have to select half of the chromosomes... you can think of it as binary numbers. You get either chromosome 0 or 1. So, there are 2^{23} combinations.

PS Im not sure how you would do it, but your calculation doesn't give a 0 probability if the average number of children per family was 1 (which it should be). Im not sure where you would incorporate this.

ou are correct, it is impossible to calculate, but the same goes for weather, or the decaying of an atom. You can still make a mathematical model which could predict an outcome based on variants. As i stated, one variant i have not included is crossing over (though if you were good at maths you could factor this in). The more things you factor in, the better the model, the better the prediction. But you can never make a perfect model.

Quote from: mpt-matthew on 13/01/2011 00:43:54PS Im not sure how you would do it, but your calculation doesn't give a 0 probability if the average number of children per family was 1 (which it should be). Im not sure where you would incorporate this. Cousins marrying Cousins?Oedipus?A stable (or healthy slowly declining) population is 1 kid per parent, or 2 kids per couple (excluding Oedipus, of course which would change your averages).Anyway, the diffusion of genes in the population is so rapid that the probability of "twins" in the general population drops to virtually zero. The problem is that in the general population, you don't have 23 or 46 chromosomes... but virtually every chromosome is unique due to random variations and cross-overs. The only way to do the calculation would be in a very tight tribal society... and still you'd need to enforce no mutations or crossovers. Did we talk about spontaneous mutations? I think the spontaneous mutation rate is on the order of a few hundred base pairs per generation.I'm still thinking the chances are 1:2^{46}, rather than 1:2^{23}. (perhaps dividing by a factor of 2).As I believe it would be the same to line up 23 maternal and 23 paternal chromosomes and dividing them... vs lining up all 46 chromosomes (keeping maternal and paternal pairs separate)... and dividing them.Or, as I discussed earlier, giving each maternal chromosome a 0/1 bit, and each paternal chromosome a 0/1 bit, thus 46 bits total.Now...An interesting calculation would be the probability of getting an "anti-twin" (without scientifically creating it).During telophase, every egg and every sperm has a pair with all the opposite chromosomes. The male sperm, without fertilization treatment, of course, would die within 9 months. But, perhaps it could happen with fraternal twins.Keep in mind that through fertilization treatment, it is relatively easy to create identical twins, either both born at the same time, or later dates.

With you now.Even so, you still have 4 possible alleles of each gene to consider, and SNPs. You could make a mathematical model for most things, but that does not mean you can exclude factors that change the numbers that you crunch.

If the average babies per couple was 1, i dont think you could have cousins, therefore 0 probability. But this is not the case, as the population (as you said) will eventually decline and die out.

By anti-twin i presume you mean another sibling from the same couple with the opposite chromosome combination of you.This would be the same probability as creating an exact twin - the probability of getting ANY gene combination is 1 in 1.76X10 ^{13}.

I'm not sure about where you get the half.I have always wondered why China's population is still increasing with a 1 child policy.True... except there will be 1 sperm, and 1 egg that has the exact opposite genes. The likelihood of the second egg getting fertilized either at the same time (fraternal twins), or during successive pregnancies is non-zero. So, if fertilization is "random", with fraternal twins, it would depend on the number of sperm per ejaculate, and would be around 1 in 280 Million (assuming both sperm are viable in the same ejaculate).For successive pregnancies, it depends on the chance of that second egg getting fertilized times the probability of the "anti-twin" sperm, which as mentioned, with no crossovers, it is actually a smaller number 1 in 2^{23} for the men (1 in 8,388,608), but in reality is a more rare case due to the crossovers.Without getting that second egg... the obviously the number is the same as the one calculated above... 1 in 70 trillion.

Do you understand how meiosis works? The DNA (which contains the alleles and SNPs) is contained on the chromosome.

Hope this helps. If you still disagree, please explain yourself more.

Not particularly because you are concentrating on making the numbers crunch whereas I am basing it on what actually happens and what is feasible. [] [] []

Even so, you still have 4 possible alleles of each gene to consider, and SNPs.