Question on human polyploid reproduction (EXTREMELY CURIOUS)

On Fri, 26 Sep 2003 03:00:26 +0000 (UTC), [email hidden] (Bobby

McGee) said:

I was wondering if it is possible for a human being with a polyploidy condition to reproduce with a
"normal" member of the population. I

Quoted message said:

cells" it made no difference to offspring. To be more specific; can someone with down's syndrome
reproduce with a person with a normal chromosomal formation? If so how does the extra chromosome 21
distribute to the offspring?

Males who have down syndrome have greatly reduced fertility and are usually impotent. There are only
a few documented cases of a male Down Syndrome individual fathering a child. Females with down
syndrome are usually fertile, and when they produce children with a normal male, 40-50% of the
offspring have down syndrome. William L Hunt

William L Hunt said:

(Bobby McGee) said:

I was wondering if it is possible for a human being with a polyploidy condition to reproduce with
a "normal" member of the population. I

Quoted message said:

Quoted message said:

cells" it made no difference to offspring. To be more specific; can someone with down's syndrome
reproduce with a person with a normal chromosomal formation? If so how does the extra chromosome
21 distribute to the offspring?

Males who have down syndrome have greatly reduced fertility and are usually impotent. There are
only a few documented cases of a male Down Syndrome individual fathering a child. Females with
down syndrome are usually fertile, and when they produce children with a normal male, 40-50% of
the offspring have down syndrome. William L Hunt

As far as I know XYY males are not less fertile, but the Y chromosome has very few genes on it. For
some reason there are more XYY males in prison compared to their numbers in the general population.
Something for the statisticians to work out.

Downs is a special case. Most trisomies aren't even viable in humans. Plants don't seem to be
bothered as much by trisomy.

Bobby McGee said:

I was wondering if it is possible for a human being with a polyploidy condition to reproduce with
a "normal" member of the population. I know

Quoted message said:

difference to offspring. To be more specific; can someone with down's syndrome reproduce with a
person with a normal chromosomal formation? If so how does the extra chromosome 21 distribute to
the offspring?

What you are talking about is aneuploidy (more specifically trisomy), with individual
chromosomes being present in too many copies. True polyploidy has ALL of the chromosomes
being present in more than 2 copies. Polyploidy without aneuploidy is possible and common in
plants and certain animals, but not in mammals. According to one of my cytogenetics
textbooks from college (I think the title was _Cytogenetics_, appropriately enough),
triploidy in humans is lethal at birth or earlier, due to X inactivation shutting down 2 X
chromosomes (or actually the non-pseudo-autosomal parts of them) in each cell, thus causing
the ratio of active X chromosomes to autosomes to be 1/3 instead of 1/2. Higher polyploidy
should be lethal even earlier in embryonic development. Therefore, polyploid mammals are
ALMOST unknown. Nevertheless, some rodent in Argentina seems to have managed to become
tetraploid -- maybe the founding members of this species simultaneously acquired a mutation
in the X inactivation system (not impossible, but extremely low probability, and thus
amazing that we find even 1 example). Plants and most non-mammalian animals, as well as
fungi and microorganisms, do not have X

dosage balancing), so many of them are considerably more tolerant of polyploidy (although they still
have to contend with the meiotic mechanism for segregating homologous chromosomes potentially
getting confused due to seeing more than 2 copies of each chromosome, but apparently that is easier
to evolve workarounds for).

--
Lucius Chiaraviglio Approximate E-mail address: [email hidden] To get the exact address: ^^^
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in article [email hidden], Lucius Chiaraviglio
at [email hidden] wrote on 10/22/03 4:33 AM:

Quoted message said:

Quoted message said:

I was wondering if it is possible for a human being with a polyploidy condition to reproduce with
a "normal" member of the population. I know

Quoted message said:

Quoted message said:

difference to offspring. To be more specific; can someone with down's syndrome reproduce with a
person with a normal chromosomal formation? If so how does the extra chromosome 21 distribute to
the offspring?

My cytogenetics is a bit rusty. At meiosis normal disomic chromosomes form bivalent chromosome. The
spindle apparatus attaches to the centromeres of each chromosome and pulls each chromosome to to
opposite ends of the cell

-------0--------- -------0---------

Phillip Smith phills@(buggger).co.nz replace bugger with ihug applied-evolution.co.nzapplied-evolution.co.nzOpen ↗

"he who is smeared with blubber has the kindest heart" -- a Greenland Eskimo adage

Trisomic individuals produce trivalents or bivalent + a univalent

-----0--------- -----0--------- -----0---------

Or -----0------ + -------0-------- -----0------ The univalents can get stuck in the middle some ties
when other chromosome separate forming laggards. Sometimes the can break at the centromere. and the
fragments can go to each pole

-----0
------
Usually at least one gamete is produced with a correct haploid complement. I am pretty sure there
are cases where trisonic individuals have reproduced. I think this is why they used to sterilised
and in some cases the females may still be. They are probably more likely to have normal children
than trisomic because of loss of univalents at meiosis and because of the higher mortality of
trisomic fetuses

Phillip Smith phills@(buggger).co.nz replace bugger with ihug applied-evolution.co.nzapplied-evolution.co.nzOpen ↗