Y Chromozome



R

Rfoy H

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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?
 
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.
 
"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.
 
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
 
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.
 
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
 
> 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?
 
"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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