Y Chromozome

Discussion in 'Health and medical' started by Rfoy H, Mar 5, 2004.

  1. Rfoy H

    Rfoy H Guest

    Recently I read an article about the Y Chromosome. It suggested that, though small compared to the
    x, it covers a lot of territory.

    It also said that it evolves rather rapidly. I haven't a clue what that really means.

    However, these statements made me wonder about the difference in genetic heritage of the male and
    female of the species.

    The male can only inherent his Y chromosome on his paternal line of ancestors, that is from, his
    father, his paternal grandfather, etc back to some dim distant ancestor. His brother will have the
    identical ancestry.

    However some other male will have a different ancestry back to some time where there is a common
    male parent, some of which will not occur in the ancestral tree until the evolution of speech.

    As a result of the rapid evolution of the Y chromosome, would it not be possible for males to have
    evolved to fill different niches within a small scale tribal social group?

    Is this reasonable?
     
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  2. Tim Tyler

    Tim Tyler Guest

    RFoy H <[email protected]> wrote or quoted:

    > As a result of the rapid evolution of the Y chromosome, would it not be
    > possible for males to have evolved to fill different niches within a small
    > scale tribal social group?
    >
    > Is this reasonable?

    I don't believe so.

    The Y chromosome evolves rapidly since:

    * it is a wasteland - with only a few dozen genes;

    The section entitled:

    ``Gene content of the human Y chromosome''

    - http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=138936

    ...says why there aren't many genes on the Y chromosome, and why most of the ones
    that are there are expressed in the testes.

    Whatever ability men have to fill different niches, it's probably got a lot more
    to do with the rest of the genome than it does with the Y chromosome.

    There is no reason for the relevant genes to be on the Y chromosome - since
    maleness is a signal that can switch the expression of genes throughout the rest
    of the genome on and off.
    --
    __________
    |im |yler http://timtyler.org/ [email protected] Remove lock to reply.
     
  3. Malcolm

    Malcolm Guest

    "RFoy H" <[email protected]> wrote in message
    > Recently I read an article about the Y Chromosome. It suggested that, though
    > small compared to the x, it covers a lot of territory.
    >
    The testis-determining factor, at the tip of the Y chromosome, has very far-
    reaching effects, changing a body from female to male. However it acts like a
    switch. The genes that build the penis, for example, probably are not on the Y
    chromosome at all.
    >
    > It also said that it evolves rather rapidly. I haven't a clue what that
    > really means.
    >
    What it means is that when you compare a Y chromosome with one from several
    hundred thousand years ago, there will be more differences than if you compare
    two autosomes. You could test this by comparing sequence homology in humans and
    chimpanzees.
    >
    > As a result of the rapid evolution of the Y chromosome, would it not be
    > possible for males to have evolved to fill different niches within a small
    > scale tribal social group?
    >
    > Is this reasonable?
    >
    Estimate the chimp-human split from Y-independent data. This then tells you how
    fast the Y-chromosome is evolving. If we assume a date of 5 million years, we can
    calibrate the Y clock. Looking at human sequences, this gives us a date for Y
    "Adam". By looking at other known human splits, for instance the colonisation of
    the Americas, we can get further calibration. What you will find is that Y Adam
    lived quite recently, and that many sub-populations also have one or maybe a
    handful of male founders. It is therefore not plausible that there is much
    maintenance of different Y chromosomes by frequency-dependent selection (i.e. one
    haplotype makes men good arrow-makers whilst another codes for witch-doctors. The
    only witch-doctor in a tribe is highly fit whilst if you have ten witch-doctors
    eight will starve, and the same for arrow-makers, so both are maintained.) This
    is not to say that this effect never happens, anywhere, but not on a large scale.
     
  4. Tim Tyler <[email protected]> writes:

    > RFoy H <[email protected]> wrote or quoted:
    >
    > > As a result of the rapid evolution of the Y chromosome,
    > > would it not be possible for males to have evolved to
    > > fill different niches within a small scale tribal social
    > > group?
    > >
    > > Is this reasonable?
    >
    > I don't believe so.
    >
    > The Y chromosome evolves rapidly since:
    >
    > * it is a wasteland - with only a few dozen genes;

    This shouldn't be a large effect, since very little of any
    of the nuclear chromosomes is subject to significant
    purifying selection (although this is one reason, among
    several, for doubting that different Y's could fill
    different niches within a single population).

    This seems like a good argument for why genes would leave
    the Y for other chromosomes, but I doubt it has much direct
    effect on the rate of evolution -- errors that matter are
    mostly removed by selection in any case. (I suppose one
    could imagine a scenario in which more mildly deleterious
    mutations persist on the Y, leading to more compensatory
    mutations. Doesn't sound like a large effect, however.)

    The causes for rapid evolution of the Y that I know of are:
    1) it has a higher mutation rate than the rest of the
    nuclear genome;
    2) it has a much smaller effective population size than the
    rest of the nuclear genome, and therefore undergoes much
    more rapid drift.

    It wasn't clear to me what the original poster meant by more
    rapid evolution -- faster drift, more substitution, more
    phenotypic change? The second cause, for example, doesn't
    affect the substitution rate (at least not at equilibrium --
    but humans are hardly at equilibrium), but the first does.

    --
    Steve Schaffner [email protected] Immediate assurance is an
    excellent sign of probable lack of insight into the topic.
    Josiah Royce
     
  5. Tim Tyler

    Tim Tyler Guest

    Steve Schaffner <[email protected]> wrote or quoted:
    > Tim Tyler <[email protected]> writes:

    > > The Y chromosome evolves rapidly since:
    > >
    > > * it is a wasteland - with only a few dozen genes;
    >
    > This shouldn't be a large effect, since very little of any
    > of the nuclear chromosomes is subject to significant
    > purifying selection (although this is one reason, among
    > several, for doubting that different Y's could fill
    > different niches within a single population).
    >

    >
    > This seems like a good argument for why genes would leave
    > the Y for other chromosomes, but I doubt it has much
    > direct effect on the rate of evolution -- errors that
    > matter are mostly removed by selection in any case. (I
    > suppose one could imagine a scenario in which more mildly
    > deleterious mutations persist on the Y, leading to more
    > compensatory mutations. Doesn't sound like a large effect,
    > however.)
    >
    > The causes for rapid evolution of the Y that I know of
    > are:
    > 1) it has a higher mutation rate than the rest of the
    > nuclear genome;

    http://www.hhmi.org/news/page4.html reports on a male-female
    mutation rate ratio of about 1.7 - based on an analysis of

    Presumably, the X-Y difference is a bit smaller than this -
    since X chromosomes also spend about 1/3 of their time in
    male bodies.
    --
    __________
    |im |yler http://timtyler.org/ [email protected] Remove
    lock to reply.
     
  6. Tim Tyler <[email protected]> writes:

    > Steve Schaffner <[email protected]> wrote or quoted:

    > > The causes for rapid evolution of the Y that I know
    > > of are:
    > > 1) it has a higher mutation rate than the rest of the
    > > nuclear genome;
    >
    > http://www.hhmi.org/news/page4.html reports on a male-
    > female mutation rate ratio of about 1.7 - based on an
    > analysis of

    Estimates of the ratio vary. The Page study you cite is the
    lowest I'm aware of; it's been attacked by Li and Makova.
    Also low were the Human Genome Project genome paper (ratio =
    ~2) and a study from Svante Paabo's group (~3). Most studies
    put the ratio at around 5. If you are interested, there are
    a number of references in

    http://www.broad.mit.edu/personal/sfs/nrg_Xchrom.pdf

    (see p. 45).

    > Presumably, the X-Y difference is a bit smaller than this
    > - since X chromosomes also spend about 1/3 of their time
    > in male bodies.

    Yes.

    --
    Steve Schaffner [email protected] Immediate assurance is an
    excellent sign of probable lack of insight into the topic.
    Josiah Royce
     
  7. Irr

    Irr Guest

    > As a result of the rapid evolution of the Y chromosome,
    > would it not be possible for males to have evolved to fill
    > different niches within a small scale tribal social group?

    Didn't I read somewhere recently of a (modern?) variation on
    this theme where the Y chromosome is found to be more
    geographically localized than X because of this idea that
    men tend to live and work not far from their families, with
    their wives relocating to accommodate? I thought there was a
    fancy (but apparently not catchy!) name for this, but is
    there any truth to it?
     
  8. "IRR" <[email protected]> writes:

    > > As a result of the rapid evolution of the Y chromosome,
    > > would it not be possible for males to have evolved to
    > > fill different niches within a small scale tribal social
    > > group?
    >
    > Didn't I read somewhere recently of a (modern?) variation
    > on this theme where the Y chromosome is found to be more
    > geographically localized than X because of this idea that
    > men tend to live and work not far from their families,
    > with their wives relocating to accommodate? I thought
    > there was a fancy (but apparently not catchy!) name for
    > this, but is there any truth to it?

    There have been a number of studies that have compared
    genetic diversity on the Y chromosome with that of mtDNA
    (very little has been done on comparing the X and the Y).
    Most, but not all, show greater population structure (larger
    differences between populations) for the Y than for mtDNA.
    This could be due to the phenomenon you mention (known as
    "patrilocality"), or to a smaller effective population size
    for the Y caused by polygyny. Or both, of course.

    --
    Steve Schaffner [email protected] Immediate assurance is an
    excellent sign of probable lack of insight into the topic.
    Josiah Royce
     
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