Genetics of male pattern baldness?

Discussion in 'Biology & Genetics' started by Dinosaur, Dec 24, 2006.

  1. Dinosaur Rational Skeptic Valued Senior Member

    The 24 December 2006 issue of the Philadelphia Inquirer has an article which says the following
    • Baldness can be inherited from either the mother's or the father's side of the family or from both sides. It may or may not skip a generation.
    It has always been my understanding that it is due to a recessive gene on the X-Chromosome. My understanding is as follows.
    • Women have a pair of X-Chromosomes, while men have an X & a Y.

    • Daughters get one X-Chromosome from the father & one from the mother. In order for the daughter to inherit baldness, she must have the gene on both X-Chromosomes.

    • If a bald father contributes a Y-Chromosome, the result is a boy, making it impossible for a son to inherit baldness from a bald father. The son could get an X-Chromosome with the gene from his mother causing him to become bald.

    • If the bald father contributes his X-Chromosome, the result is a girl. The girl will become bald if the X-Chromosome from her mother also carries the gene. Grandsons of the bald man via his bald daughter will inherit the gene and become bald (The gene could come from either side of the family). Granddaughters will be carriers of the recessive gene, but will only be bald if their father is bald.

    • If the bald father contributes his X-Chromosome and the mother contributes an X-Chromosome without the gene, the girl will not become bald (gene is recessive), but has a 50-50 chance of passing the gene to a son, making him bald.

    • A woman requires a bald father and a bald grandfather to have a 50-50 change of becoming bald.

    • A man requires only a bald grandfather to have a 50-50 chance of becoming bald (assuming that his mother is not bald).
    The above are the rules for sex-linked inheritance of recessive characteristics. If male pattern baldness is a sex linked characteristics, the above should be correct.

    Does the above describe the normal inheritance for male pattern baldness? It seems consistent with the rarity of female baldness compared to the frequency of male baldness.

    Is there some other type of inheritable baldness which does not follow the above rules?

    BTW: It is my understanding that hemophilia, left handedness, and some types of color blindness also follow the above rules.
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  3. ddovala Pi is exactly 3 Registered Senior Member

    An interesting theory.

    However, my understanding is that baldness is an autosomal trait. The dimorphism you find between men and women can be explained by "sex-influence". Sex influence affects the heterozygote of the gene. For example, if the baldness gene is denoted B, then it would show the following pattern:

    ..........Men ..........Women
    BB....not bald .......not bald
    Bb..... bald ...........not bald
    bb .....bald .............bald (rather -- thinned out hair)

    The chemical reasoning for this has to do, I believe, with testosterone levels. Higher levels in men, along with the defective gene, lead to hair falling out.

    You are correct about hemophilia and color blindness -- it is a classical example of an X-linked recessive trait. (There might be autosomally derived versions too -- I'm not sure. Clotting is a long pathway and only one gene in the pathway needs to be knocked out for hemophelia to occur. The vast majority of hemophilia cases though, as I have been told, are linked to the X chromosome)

    I have no idea about left handedness
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  5. The Devil Inside Banned Banned

    im ambidextrous.

    i do most things fairly equally with my left and right hands, with nearly equal proficiency.... it is because i trained myself to be that way, not because of genetics.

    im also balding.

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  7. francois Schwat? Registered Senior Member

    I've heard that apes are ambidextrous as well.

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  8. superluminal I am MalcomR Valued Senior Member

    Right handed and balding.

    The genetics of it goes like this:

    The dimorphic fu complex is autosomal dominant on the X chromosome at the GDIGB (god damnit i'm going bald) replication site. There is also a series of methylation sites that influence the whether you will be attractively bald (like captain piccard) or hideously bald (like me).
  9. The Devil Inside Banned Banned

    "be like those before you", i suppose.

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  10. S.A.M. uniquely dreadful Valued Senior Member

    Intriguing. I'm still waiting on the close up sans glasses.

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