Why is my brother different from me?

Discussion in 'Biology & Genetics' started by Magical Realist, Mar 25, 2015.

  1. Magical Realist Valued Senior Member

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    We come from the exact same DNA. So how is it that I am different from my brother? What causes this huge variability in how the two strands of my parent's DNA fuses together? Also, how much DNA is the same between me and my brother?
     
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  3. Fraggle Rocker Staff Member

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    The only way to determine how much DNA you and your brother share is to analyze it. This is quite possible and it's done every day. This is how they resolve paternity suits, for example.

    However, any two humans share the vast majority of their DNA. I'm not certain what the figure is, but I'm certain that if one person has less than, say, 95% of the same DNA that you have, then he is not actually a human person, but another species of ape. Even a banana tree has almost 50% of the same DNA that you have. All living things--animals, plants, fungi, algae, bacteria and archaea--are descended from the same ultra-simple living organisms that arose several billion years ago. The differences among the species are generally due to errors in reproduction, for example due to the effect of cosmic rays. We call these mutations. This is why all organisms share so much of their DNA. You can't toss the molecules around and reassemble them just any way you want, or you'll end up with something that is simply not alive.

    If it turns out that all humans share 98% of their DNA, then that only leaves 2% that you and your brother inherited specifically from your parents, differentiating you genetically from other family groups. In this case, probability indicates that, on the average, two brothers would share 99% of their DNA.

    Again, please bear in mind that my figures are all estimates based on things I vaguely remember. I could be way off, in which case all humans might share as much as 99.9% of their DNA, or as little as 97%.

    If a real biologist jumps into this discussion, you can believe his figures and ignore mine.

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  5. Daecon Kiwi fruit Valued Senior Member

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    You have half of your mother's chromosomes (23/46), and half of your father's chromosomes (23/46).

    So does your brother.

    They're probably not exactly the same 23 chromosomes from each parent, unless you were identical twins.
     
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  7. Kittamaru Now nearly 40 pounds lighter. Staff Member

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    Keep in mind, you have to separate the autosomal DNA (that which is NOT carried on the X and Y chromosomes) from the specific DNA that dictates how we look/gender/etc.

    http://freepages.genealogy.rootsweb.ancestry.com/~laetoli/degree.html

     
  8. Kittamaru Now nearly 40 pounds lighter. Staff Member

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    It is worth pointing out - you would only come from the exact same DNA if you are Maternal twins (that is, one egg fertilized by one sperm that split into two zygotes).

    Two different sperm can have two different DNA: When sperm or eggs are created, half the DNA of your body goes into it - however, it's like taking 46 cards (representing the 46 chromosomes) and shuffling them, then drawing 23 cards (the 23 chromosomes each reproductive cell, Egg or Sperm, carries) randomly to get a stack of cards (one reproductive cell)
     
  9. joepistole Deacon Blues Valued Senior Member

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    One word, milkman.
     
  10. Magical Realist Valued Senior Member

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    LOL! Maybe the vacuum cleaner salesman too..
     
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  11. Fraggle Rocker Staff Member

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    That's all done online now.

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