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Thread: relationship clarification

  1. #1 relationship clarification 
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    The problem with interbreeding is the lack of genetic diversity in DNA right? So the only problem with inter family is the resemblance in DNA, if this is the case then a distant cousin may be ok (not talking morals or ethics here) and people who have a lot in common may even be worse as they may have similar DNA codes.I posed this question to my teacher but he told me it had to do with blood as well. How can this be if blood is all created according to the DNA anyway? How can blood be different in similar DNA?


    just wondering
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  3. #2 Re: relationship clarification 
    Moderator Moderator TheBiologista's Avatar
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    Quote Originally Posted by zendra
    The problem with interbreeding is the lack of genetic diversity in DNA right? So the only problem with inter family is the resemblance in DNA, if this is the case then a distant cousin may be ok (not talking morals or ethics here) and people who have a lot in common may even be worse as they may have similar DNA codes.I posed this question to my teacher but he told me it had to do with blood as well. How can this be if blood is all created according to the DNA anyway? How can blood be different in similar DNA?
    Nothing to do with blood, or at least no more so than any other part of us. The problem with inbreeding is this. Every human has two copies of each gene, one inherited from their father and the other from their mother. We call different versions of a gene "alleles". Alleles are mutated versions of the original gene but are generally not harmful if they are common in the population. You have for example two alleles that code for eye colour. So which one determines your actual eye colour? Alleles may be dominant, co-dominant or recessive relative to each other. So for eye colour, blue may be dominant to green and brown may be dominant to blue and green, which is to say that blue and green are recessive relative to brown (the actual real world relationships may not be so simple but lets just accept this for now). So, if you inherit a blue allele and a brown allele, your eyes will be brown. Similarly, if you get a blue allele and a green allele, your eyes will be blue. How do you get green eyes? Only if you inherit two green alleles. When we have inherited two different alleles, we say that we are heterozygous for that gene. When we get two of the same allele, we are homozygous.

    Most people are born with a few dangerous mutations but most mutations to a gene are recessive relative to the ones that currently exist. So although we might inherit a detrimental allele from one of our parents, the odds are very good that we'll inherit a dominant fully functional allele from the other parent and so the detrimental allele will not be expressed. But imagine what would happen if our parents were related- they share a certain percentage of identical alleles, including some detrimental ones. Now the odds are much higher that we will inherit two copies of a detrimental allele. Just like the example where a person homozygous for the green eye allele expresses that rare phenotype, so too would we express the detrimental gene.

    Indeed, because siblings and cousins share so many alleles, there's a very good chance that they'll inherit multiple different pairs of such alleles. Some such mutations may have to do with blood, but as I said, this is no more likely than any other organ. What your teacher may have been referring to is one of the more famous such mutations- haemophilia, a set of disorders whereby the sufferer has trouble making blood clots. This disorder was inherited into one of the royal families of Europe and, because the various royal families of Europe tended to inbreed closely to maintain alliances and heal feuds, inbreeding-related problems were common, including the blood disorder haemophilia.

    Hope this has been helpful. Some extra reading, of you're interested:

    http://en.wikipedia.org/wiki/Genetic_dominance
    http://en.wikipedia.org/wiki/Inbreeding
    http://en.wikipedia.org/wiki/Hemophilia


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    cool thanks
    just wondering
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