Home |
Search |
Today's Posts |
#1
|
|||
|
|||
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? |
#2
|
|||
|
|||
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 |
#3
|
|||
|
|||
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 |
#4
|
|||
|
|||
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 |
#5
|
|||
|
|||
Chromosome variants?
BTW...I found a great graphics and explanation of reciprocal and
Robertsonian translocations at http://dictionary.laborlawtalk.com/C..._translocation |
#6
|
|||
|
|||
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. |
#7
|
|||
|
|||
Chromosome variants?
|
#8
|
|||
|
|||
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. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Mericloning (and chromosome counting) | Orchids |