posted
The XY chromosome arrangement is universal among mammals (to the best of my knowledge), and some other groups have a similar method (some insects, for instance). However, other vertebrates use different methods. In birds, the reverse is true (and Z & W are used); a female bird has the ZW karyotype, a male ZZ. Among reptiles, amphibians, and fish the method varies widely. Some are chromosomally determined, some are determined by genes on normal paired chromosomes, and some are determined by environmental factors. Crocodilians, for instance, are at risk because their sex is determined by temperature before hatching. An environment that becomes too hot or too cold will result in all offspring being of the same sex.
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Oh, and something else: only two trisomies not involving the sex chromosomes are nonlethal (Down's syndrome and another very similiar condition; I don't recall the chromosome numbers), and every monosomy except Turner's Syndrome (XO) is also lethal. I do not have any research before me, but I would be surprised if the same was not true for most animal species.
So it would be very unlikely to produce a new species by this means, at least among animals. There are a few animal species that are polyploid (they have more than one entire set of chromosomes), such as parthenogenetic whiptail lizards. It might be worth taking note of that aside from the parthenogenesis, these species are virtually identical to other whiptail lizards. In fact, being essentially clones of each other, further evolution would have to be very very slow. There is no sexual recombination occurring, so all that is left is mutation.
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posted
I beleive it is Trisomy 18. When i worked for UCP, there was a little girl with T18. I remember that at the age of three, she had the size and developmental ability of a two moth old. Sadly, she died at 7.
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posted
Hmmm...my reading indicates that there are some children with other trisomies who live for some time. This site indicates that certain children also have trisomy 13 and 14, and possibly others. Still, these children tend to die very young; they certainly do not reach maturity and reproduce. I hate to discuss it so clinically--the death of children is very saddening--but that is the topic, and it is important.
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posted
The lower the number of the gene the trisomy occurs on, the greater the defectc and the shorter the lifespan. I think that Angelman's is caused by Trisomy 15.
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posted
The smaller the chromosome number, the larger the chromosome (and therefore the more DNA it contains). This means that the smaller the number of the chromosome with trisomy, the less likely of survival.
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posted
from most of his books his religion doesnt look like it has limitation over his writing. but there still good Posts: 12 | Registered: Mar 2004
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