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Old 13-11-2006, 10:19 PM posted to sci.bio.botany
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Default Chromosome variants?

While Homo sapiens usually have 46 chromosomes there are individuals
with 45 chromosomes (Turner's syndrome), 47 chromosomes (Down,
Klinefelter's, XYY and XXY syndromes) and even 48 chromosomes (XXYY
syndrome). Most of these variants are fertile and able - with
individuals with the "normal" complement of 46 chromosomes - to produce
children.

Are there other species also with a variant chromosome count? Or do we
know? Homo sapiens is, no doubt, the species we know most about and
maybe such variation has eluded detection in other species?

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Old 13-11-2006, 11:47 PM posted to sci.bio.botany
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Default Chromosome variants?

"Raphanus" wrote in message
ups.com...
While Homo sapiens usually have 46 chromosomes there are individuals
with 45 chromosomes (Turner's syndrome), 47 chromosomes (Down,
Klinefelter's, XYY and XXY syndromes) and even 48 chromosomes (XXYY
syndrome). Most of these variants are fertile and able - with
individuals with the "normal" complement of 46 chromosomes - to produce
children.


These above are cases with an extra one [or a shortage of one] of the
usual set chromosomes; the term is "trisomy". There have also been
human examples where two of the usual chomosome complement have
essentially fused to become one, or one has split to become two.

http://groups.google.com/group/talk....3decba44c19721

These latter types of changes are more relevant to the chromosomal
changes seen in evolving lineages than trisomies. A fusion of two
ancestral chromosomes that are still separate in the other great apes
is recognized to have occurred within the human lineage at some point
since our last common ancestor with chimpanzees.

http://www.gate.net/~rwms/hum_ape_chrom.html

Are there other species also with a variant chromosome count? Or do we
know? Homo sapiens is, no doubt, the species we know most about and
maybe such variation has eluded detection in other species?


There are different kinds of chromosome changes and chromosomal
variants, and they are well known in many species, including plants
and animals. There are numerous species known with chromosomal
polymorphisms and two or a whole range of different chromosome
numbers known within a single biological species.

http://groups.google.com/group/talk....98937b7a3161fb
http://groups.google.com/group/talk....c6e6cf5b4c9ceb
http://groups.google.com/group/talk....7bb981b4a5e2ac
http://groups.google.com/group/talk....ef84ad8e77ed77

Individuals "heterozygous" for different chromosomal configurations
may still be highly fertile, if two chromosomes of one set can still
pair up at meiosis with the corresponding one chromosome of the other
set.

Yet another form of chromosomal change that is especially important
in plants is polyploidy, where whole sets of ancestral chromosomes
are duplicated. It is one form of rapid new-species formation.
Many examples are well-known. Often, a new polyploid species was
derived from a hybrid between two ancestral species; the term for
this is "allopolyploidy".

cheers


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Old 14-11-2006, 12:01 AM posted to sci.bio.botany
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Default Chromosome variants?

In message . com,
Raphanus writes
While Homo sapiens usually have 46 chromosomes there are individuals
with 45 chromosomes (Turner's syndrome), 47 chromosomes (Down,
Klinefelter's, XYY and XXY syndromes) and even 48 chromosomes (XXYY
syndrome). Most of these variants are fertile and able - with
individuals with the "normal" complement of 46 chromosomes - to produce
children.

Are there other species also with a variant chromosome count? Or do we
know? Homo sapiens is, no doubt, the species we know most about and
maybe such variation has eluded detection in other species?


Yes. Google for "chromosomal races". Rodents and shrews have a tendency
to throw up species with varying chromosome numbers. (But these tend to
be chromosomal fusions or fissions, rather than deletions or
duplications.)

For plants Google for "supplementary chromosomes" or "B chromosomes",
which refers to the case where plants have a variable number of small
chromosomes in addition to the main set. Also "cytotypes", which refers
to different chromosomal conditions - typically ploidy level. (I expect
that in most cases populations with different ploidy levels represent
different species, but plant taxonomists often treat them as elements of
a single species.)

Well known plants with diploid and tetraploid cytotypes include the
lesser celandine (Ranunculus ficaria) and the yellow archangel (Lamium
galeobdolon).


--
Stewart Robert Hinsley
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Old 14-11-2006, 03:00 AM posted to sci.bio.botany
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Default Chromosome variants?

Mel and Stewart...Thanks again for educating me. You've given me much
to study. I appreciate your patience. I'm having a
"letters-to-the-editor" duel with a local "creationist" - plus a
"new-found" retirement hobby of (amateur) botany. They seemed to
merge. I'm a Ph.D. physicist and if you have a question about "strange
quarks" .... :-)


Stewart Robert Hinsley wrote:
In message . com,
Raphanus writes
While Homo sapiens usually have 46 chromosomes there are individuals
with 45 chromosomes (Turner's syndrome), 47 chromosomes (Down,
Klinefelter's, XYY and XXY syndromes) and even 48 chromosomes (XXYY
syndrome). Most of these variants are fertile and able - with
individuals with the "normal" complement of 46 chromosomes - to produce
children.

Are there other species also with a variant chromosome count? Or do we
know? Homo sapiens is, no doubt, the species we know most about and
maybe such variation has eluded detection in other species?


Yes. Google for "chromosomal races". Rodents and shrews have a tendency
to throw up species with varying chromosome numbers. (But these tend to
be chromosomal fusions or fissions, rather than deletions or
duplications.)

For plants Google for "supplementary chromosomes" or "B chromosomes",
which refers to the case where plants have a variable number of small
chromosomes in addition to the main set. Also "cytotypes", which refers
to different chromosomal conditions - typically ploidy level. (I expect
that in most cases populations with different ploidy levels represent
different species, but plant taxonomists often treat them as elements of
a single species.)

Well known plants with diploid and tetraploid cytotypes include the
lesser celandine (Ranunculus ficaria) and the yellow archangel (Lamium
galeobdolon).


--
Stewart Robert Hinsley


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Old 14-11-2006, 03:38 AM posted to sci.bio.botany
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Default Chromosome variants?

BTW...I found a great graphics and explanation of reciprocal and
Robertsonian translocations at

http://dictionary.laborlawtalk.com/C..._translocation



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Old 14-11-2006, 04:27 AM posted to sci.bio.botany
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Default Chromosome variants?

In article . com,
Raphanus wrote:
While Homo sapiens usually have 46 chromosomes there are individuals
with 45 chromosomes (Turner's syndrome), 47 chromosomes (Down,
Klinefelter's, XYY and XXY syndromes) and even 48 chromosomes (XXYY
syndrome). Most of these variants are fertile and able - with
individuals with the "normal" complement of 46 chromosomes - to produce
children.


Actually, with the exception of XYY, most of these variants are infertile,
usually due to defective development of the reproductive system, among
other physical defects. Trisomies of other chromosomes are known in
humans, but they are invariably fatal either before birth or shortly
after. In general mammals seem to be too finely tuned to work as
aneuploids or polyploids, although some amphibians have complicated
systems of interbreeding between species that result in fertile
polyploids.

Polyploid plants are often more robust than the originals, and seem
to be fertile as long as it's an even numbered ploidy. Many domestic
plants are polyploids -- selected for that robustness over millenia
of domestication. Polyploidy is a well known method of speciation
in plants.

Are there other species also with a variant chromosome count? Or do we
know? Homo sapiens is, no doubt, the species we know most about and
maybe such variation has eluded detection in other species?


Ah, the mystery of the male calico cat, very rare and usually infertile,
These animals are XXY (or mosaics) -- they have Klinefelter's syndrome.
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Old 14-11-2006, 03:25 PM posted to sci.bio.botany
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Default Chromosome variants?

My web source said that Down syndrome and XXX were also fertile. Not
true?

wrote:
In article . com,
Raphanus wrote:
While Homo sapiens usually have 46 chromosomes there are individuals
with 45 chromosomes (Turner's syndrome), 47 chromosomes (Down,
Klinefelter's, XYY and XXY syndromes) and even 48 chromosomes (XXYY
syndrome). Most of these variants are fertile and able - with
individuals with the "normal" complement of 46 chromosomes - to produce
children.


Actually, with the exception of XYY, most of these variants are infertile,
usually due to defective development of the reproductive system, among
other physical defects. Trisomies of other chromosomes are known in
humans, but they are invariably fatal either before birth or shortly
after. In general mammals seem to be too finely tuned to work as
aneuploids or polyploids, although some amphibians have complicated
systems of interbreeding between species that result in fertile
polyploids.

Polyploid plants are often more robust than the originals, and seem
to be fertile as long as it's an even numbered ploidy. Many domestic
plants are polyploids -- selected for that robustness over millenia
of domestication. Polyploidy is a well known method of speciation
in plants.

Are there other species also with a variant chromosome count? Or do we
know? Homo sapiens is, no doubt, the species we know most about and
maybe such variation has eluded detection in other species?


Ah, the mystery of the male calico cat, very rare and usually infertile,
These animals are XXY (or mosaics) -- they have Klinefelter's syndrome.


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Old 28-11-2006, 06:28 PM posted to sci.bio.botany
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Default Chromosome variants?


Raphanus wrote:

X-No-Archive
My web source said that Down syndrome and XXX were also fertile. Not
true?


One of the X chromosomes only is usually switched on in a female cell.
You see the effect in tortoiseshell cats where two of the colours are X
encoded. You get patches of colour.

Down Syndrome women have been known to give birth.

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