Y Chromozome

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

Quoted message said:

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''

- pubmedcentral.nih.govarticlerender.fcgiOpen ↗

...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 timtyler.orgtimtyler.orgOpen ↗ [email hidden] Remove lock to reply.

"RFoy H" <[email hidden]> wrote in message

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

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 said:

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

Quoted message said:

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 hidden] Immediate assurance is an
excellent sign of probable lack of insight into the topic.
Josiah Royce

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

Quoted message said:

Tim Tyler <[email hidden]> writes:

Quoted message said:

Quoted message said:

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).

Quoted message said:

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;

hhmi.orgpage4.htmlOpen ↗ 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 timtyler.orgtimtyler.orgOpen ↗ [email hidden] Remove
lock to reply.

Tim Tyler said:

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

Quoted message said:

Quoted message said:

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;

hhmi.orgpage4.htmlOpen ↗ 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

broad.mit.edunrg Xchrom.pdfOpen ↗

(see p. 45).

Quoted message said:

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 hidden] Immediate assurance is an
excellent sign of probable lack of insight into the topic.
Josiah Royce

Quoted message said:

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 said:

Quoted message said:

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 hidden] Immediate assurance is an
excellent sign of probable lack of insight into the topic.
Josiah Royce