Without recombination what are the chances that my parents could conceive anothe!


Question: Each parent has 46 chromosomes in 23 pairs: two of #1, two of #2, two of #3, and so on. Your mother gives you one #1, one #2, etc, where each egg gets a different random combination - kind of like flipping a coin 23 times, and keeping track of the exact sequence of heads and tails, choosing one or the other of each chromosome. There are a bit over 8 million combinations of chromosomes your mother could have given your.

Same with your father, except for the X/Y chromosome. You (a girl) got the X and not the Y, so only the other 22 chromosomes are in the coin-tossing game. That's about 4 million. Between your mother and father, that's 45 coin flips, or about 32 trillion possible combinations - about five thousand times the population of the planet.

Let's assume there are no lethal recessives to worry about, or immunological incompatibility with the mother (like Rh disease, but there are others), and you already disqualified recombination. If your parents kept having kids until they had another one just like you, genetically, that would be about half of 32 trillion (in some statistical sense), or 16 trillion - more than 2000 times the Earth's population. A slightly different question would ask: when would they have two kids with identical chromosomes, not necessarily yours, but that's a "birthday paradox" question. They'd have to have 5-6 million kids to get an even chance of some two among all those having the same chromosomes.

Long before that, your mother would have had your father sterilized at gunpoint.

All that ignores gene silencing. Especially on the X chromosomes, you get a double dose of each gene, but not necessarily the same allele. (An allele is a different version of a gene, like the A blood type vs. B blood type.) It's bad to have genes too active, so gene silencing attaches a marker to the gene on one chromosome or the other, telling it to hush up. If the two copies of that gene are different alleles, then silencing one instead of the other results in a different phenotype. I don't know how many genes are subject to gene silencing, but there are a few. That's why identical (monozygotic) twins aren't 100% identical, and why girl monozygotics are more different from each other than boys - they have more X genes to choose from when the gene silencing happens. I don't know the numbers, but gene silencing means that there are lots more than 32 trillion possibilities - maybe thousands or millions times as many different possibilities.

Even if they got lucky on the 1:32,000,000,000,000 chance, and even if gene silencing somehow picked the same set of genes to silence, where the alleles are different, environment and experience would make you into different people. Two of my cousins are monozygotic twins, but you'd never know it to look at them. Life has treated them very differently, and it shows.

Rest easy. You're unique. You are the only you there is, and always will be.


Answers: Each parent has 46 chromosomes in 23 pairs: two of #1, two of #2, two of #3, and so on. Your mother gives you one #1, one #2, etc, where each egg gets a different random combination - kind of like flipping a coin 23 times, and keeping track of the exact sequence of heads and tails, choosing one or the other of each chromosome. There are a bit over 8 million combinations of chromosomes your mother could have given your.

Same with your father, except for the X/Y chromosome. You (a girl) got the X and not the Y, so only the other 22 chromosomes are in the coin-tossing game. That's about 4 million. Between your mother and father, that's 45 coin flips, or about 32 trillion possible combinations - about five thousand times the population of the planet.

Let's assume there are no lethal recessives to worry about, or immunological incompatibility with the mother (like Rh disease, but there are others), and you already disqualified recombination. If your parents kept having kids until they had another one just like you, genetically, that would be about half of 32 trillion (in some statistical sense), or 16 trillion - more than 2000 times the Earth's population. A slightly different question would ask: when would they have two kids with identical chromosomes, not necessarily yours, but that's a "birthday paradox" question. They'd have to have 5-6 million kids to get an even chance of some two among all those having the same chromosomes.

Long before that, your mother would have had your father sterilized at gunpoint.

All that ignores gene silencing. Especially on the X chromosomes, you get a double dose of each gene, but not necessarily the same allele. (An allele is a different version of a gene, like the A blood type vs. B blood type.) It's bad to have genes too active, so gene silencing attaches a marker to the gene on one chromosome or the other, telling it to hush up. If the two copies of that gene are different alleles, then silencing one instead of the other results in a different phenotype. I don't know how many genes are subject to gene silencing, but there are a few. That's why identical (monozygotic) twins aren't 100% identical, and why girl monozygotics are more different from each other than boys - they have more X genes to choose from when the gene silencing happens. I don't know the numbers, but gene silencing means that there are lots more than 32 trillion possibilities - maybe thousands or millions times as many different possibilities.

Even if they got lucky on the 1:32,000,000,000,000 chance, and even if gene silencing somehow picked the same set of genes to silence, where the alleles are different, environment and experience would make you into different people. Two of my cousins are monozygotic twins, but you'd never know it to look at them. Life has treated them very differently, and it shows.

Rest easy. You're unique. You are the only you there is, and always will be.

cloning.

I don't know because I'm too lazy to work it out, but I'm guessing it would be one in several billion.

That's assuming that there's another egg inside your mother that was the same as yours...now I think about it I don't know if this happens or not. So it might not be possible. But theoretically it is, like I said really tiny chance though.

It's impossible to have someone identical to you, unless they are your identical twin.

Siblings have different DNA.





The consumer health information on answer-health.com is for informational purposes only and is not a substitute for medical advice or treatment for any medical conditions.
The answer content post by the user, if contains the copyright content please contact us, we will immediately remove it.
Copyright © 2007-2011 answer-health.com -   Terms of Use -   Contact us

Health Categories