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chromosomes

Discussion in 'MCAT: Medical College Admissions Test' started by 134317, Feb 13, 2007.

  1. 134317

    134317 Guest

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    I just want to clear something up about chromosomes, and the fact that humans have 22.

    How much genetic information is in each of the 22 chromosomes? Is there different information on each one? And does every (diploid) human cell carry these 22 chromosomes?

    Thanks in advance.
     
  2. BigRedPremed

    BigRedPremed Senior Member
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    Humans have 46 chromosomes, 2 sets of 23 homologous chromosomes.
     
  3. OP
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    134317

    134317 Guest

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    Thanks for the response. But does each chromosome have different genetic information in it?
     
  4. mc4435

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    Yes, 2 copies of 23 chromosomes in every single cell (except germ cells and some immune cells). And each chromosome has different information, yes.

    Oh and one more exception, female cells have one of their X chromosomes disabled (barr body), maybe that is where you got the 22?
     
  5. OP
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    134317

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    no. I was just straight up confused. Had Down syndrome on my mind.
     
  6. inthemiddle

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    There are 22 sets of autosomal chromosomes, which basically means they are non-sex chromosomes. And then we have one pair of sex chromosomes. And yeah, they have different information, which is where genetic diseases like Down Syndrome come from- because they have a mutation in a specific chromosome.

    Also remember that these sets are essentially the same chromosome in their type and location of genes, but differ in their alleles of those genes (dominant, recessive, all that jazz). I hope that helps a bit! :luck:
     
  7. Foghorn

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    Yes, each chromosome has different genetic information on it. The human genome is ~ 3 billion bases in length. There are ~ 30, 000 different genes dispersed throughout all the chromosomes. The haploid # for chromosomes in humans is 22 autosomal, and 2 different types of sex chromosomes.

    Down syndrome is a trisomic disease, i.e. there's an extra copy of chromosome 21, which can due to non-disjunction during meiosis. When the egg or sperm, that has the extra chromosomal copy, fuses with its counterpart during fertilization, the resulting zygote has 3 copies of chromosome 21. Trisomy is a form of polyploidy.

    Hope that helps.
     
  8. mvenus929

    Physician 10+ Year Member

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    Other diseases resulting from nondisjunction are Turners (just an X sex chromosome, nothing else), Kleinfelters (XXY), and there's one that's XYY, but I can't remember the name off the top of my head. But if you have nondisjunction on some of the bigger chromosomes (like... chromosome 1), the cell will die because it is missing or has too much information. At least, according to my cell bio and genetics professors...
     
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  9. Wizard of Oz

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    The 3 billion base pairs is the haploid set BTW, so the full complement will have twice that many; 4 times if the chromosomes have replicated. They keep reducing the total gene number. When I was in college, they were saying 100,000 per haploid set. Lately I heard 30,000; wikipedia is reporting 20,000-24,000.

    Here's a bit of trivia... We have one fewer chromosome than the other great apes because our chromosome 2 is a fusion of 2 chromosomes seen in the other apes. So chimpanzees have 24. Indeed, if you look at our chromosome 2, you can see where the former telomeres were. Am I the only one who thinks that's totally cool?
     
  10. phospho

    phospho SDN Lifetime Donor
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  11. mvenus929

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