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    Sorry but I don't study biology at all, im more of a physics person tbh, but can someone help with these questions?:
    (This isn't my homework i'm making you to do or anything... just confused.)


    Firstly,
    Why do genetic diseases exist if evolution would make carriers of these people less evolutionarily fit?

    Secondly,
    In the selfish gene it says that the chances of my brother having a gene that I have is 50%, no matter how prevalent a gene is in the popluation?

    Thirdly,
    What is a gene?

    Fourthly, probably related to 2;
    In psychology a level the twin method assumes that if a trait is fully genetic, then a DZ twin would have a 50% chance of having the trait and a MZ twin would have 100% of having that twin. However there isn't a 50% chance that my brother has two legs, or eyes, or arms. Hmm...

    If anyone knows a good book on genetics to reccomend that would be helpful thanks
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    (Original post by Jacke02)
    Firstly,
    Why do genetic diseases exist if evolution would make carriers of these people less evolutionarily fit?
    Evolution doesn't cause genetic disease, it's the other way round...mutations cause genetic conditions which then affect the evolution of a species. That said mutation is often a good thing as it allows a species to survive in a hostile environment which we see a lot with bacteria.

    Secondly,
    In the selfish gene it says that the chances of my brother having a gene that I have is 50%, no matter how prevalent a gene is in the popluation?
    I haven't read the book, but this sounds a bit vague but I imagine it's referring to how you inherit half of your chromosomes (where the DNA is) from your mother and half from your father.

    Thirdly,
    What is a gene?
    Simply: a section of DNA which codes for the production of a protein.

    e.g. the dystrophin gene codes for the production of the dystrophin protein. When this gene is faulty and mutated, dystrophin protein is deficient or not produced leading to muscular dystrophy (as an example of a genetic condition).

    Fourthly, probably related to 2;
    In psychology a level the twin method assumes that if a trait is fully genetic, then a DZ twin would have a 50% chance of having the trait and a MZ twin would have 100% of having that twin. However there isn't a 50% chance that my brother has two legs, or eyes, or arms. Hmm..
    I'm a bit unsure of what you're getting at over here, but like I said above there's no such thing as a "leg" gene...gene's code for proteins. But if we're talking about normal Mendelian inheritance, then yes, traits e.g. wrinkled vs round peas can be dominant/recessive and heterozygous/homozygous.

    http://www.experiment-resources.com/...gregation.html

    If anyone knows a good book on genetics to reccomend that would be helpful thanks
    What level are you at right now? A level? Undergrad?
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    (Original post by Democracy)
    Evolution doesn't cause genetic disease, it's the other way round...mutations cause genetic conditions which then affect the evolution of a species. That said mutation is often a good thing as it allows a species to survive in a hostile environment which we see a lot with bacteria.
    Well surely wouldn't evolution select those without these diseases? I guess if they are quite rare it dm...

    And the second point was that If a gene was very common in a population, surely there would be a greater than 50% chance that it would be in a brother?
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    Oh and a book at an introductory level i mean...... not too simple though. I'm at A Level and i want to do some pre-reading for a possible bio anthropology option for a psych degree.
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    (Original post by Jacke02)
    Oh and a book at an introductory level i mean...... not too simple though. I'm at A Level and i want to do some pre-reading for a possible bio anthropology option for a psych degree.
    I can recommend 'Language of the Genes' by Steve Jones. I've almost finished it, it is good for people who are interested in genetics. It shows you genetics for beginners and gives an interesting background of humans. I'm doing Biology A2, it covers a few things in class and a lot more advanced stuff as well.
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    heya on the issue of genetic diseases you are correct genetic diseases are selected against. However many are recessive so are present in the population as carriers people with a "normal" dominant gene and the "abnormal" gene can pass on the disease causing gene to offspring and produce more carriers.

    You also have to remember evolution can only act on a reproductively active population, so genetic diseases that act on the older non-reproducing parts of the lifecycle dont get selected against, for example age related diseases and late onset diseases like huntingtons. So some genetic diseases exist just because there is no selection pressure.

    Thirdly we have genetic diseases with adaptive benefits, for example sickle cell anemia. to put it simply a carrier (someone with one copy of the disease causing gene) is more resistant to malaria if they mate with another carrier 50% of children will be resistant 25% will be normal and 25% will suffer from the disease often terminally so. But having the gene in the population increases reproductive success or average fitness (normally defined as the measure of reproductive success) so is selected for.

    hope this clears up the disease issue the other stuff will be in any entry level textbook.
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    (Original post by Jacke02)
    Well surely wouldn't evolution select those without these diseases? I guess if they are quite rare it dm...

    And the second point was that If a gene was very common in a population, surely there would be a greater than 50% chance that it would be in a brother?
    what about if that genetic disorder had some other benefit, like Sickle-cell disease and the benefit it gives to malaria, more tolerant of infection

    of genetic disorders that show late like Huntington's disease, by the time you are showing symptoms you could have already father children then comes the question of genetic screening, i wrote a whole essay on the ethics off that :p:


    (Original post by archonhades)

    Thirdly we have genetic diseases with adaptive benefits, for example sickle cell anemia. to put it simply a carrier (someone with one copy of the disease causing gene) is more resistant to malaria if they mate with another carrier 50% of children will be resistant 25% will be normal and 25% will suffer from the disease often terminally so. But having the gene in the population increases reproductive success or average fitness (normally defined as the measure of reproductive success) so is selected for.
    not more resistant more tolerant of infection :p:
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    Cheers everyone, I'll try and find the confusing passage in Selfish Gene which I was asking about too All i remember is that he said that the probability of a brother having the same gene as you is the same, no matter how prevalent that gene in the population is.


    (Original post by Eloades11)
    I can recommend 'Language of the Genes' by Steve Jones. I've almost finished it, it is good for people who are interested in genetics. It shows you genetics for beginners and gives an interesting background of humans. I'm doing Biology A2, it covers a few things in class and a lot more advanced stuff as well.
    Oh I'll look this up. Is the book just prose or has it got pictures and stuff in to? I'll lose attention without pictures
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    (Original post by Jacke02)
    Oh I'll look this up. Is the book just prose or has it got pictures and stuff in to? I'll lose attention without pictures
    Haven't managed to spot any pictures in it, sorry
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    (Original post by Jacke02)
    Well surely wouldn't evolution select those without these diseases? I guess if they are quite rare it dm...

    And the second point was that If a gene was very common in a population, surely there would be a greater than 50% chance that it would be in a brother?
    Most of these diseases are caused by recessive genes - people can carry one copy of the gene without having any real harmful effects, and pass that gene on.

    Also in some cases it's more complicated. Example - sickle cell anaemia. Having two copies of the gene means you have the disease. Having one copy provides some measure of protection against malaria.

    EDIT the first: As I read down this thread I find someone beat me to this one. A-level biology win .
 
 
 
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