Deborah Harrell wrote: > >>> A chromosomal mutation like Down's (trisomy 21), >> >> It's not a mutation. Trisomy means that the 21 >> chromosome gets a third _copy_. Mutation >> means that a gene is alterered. > ><nitpick> >Well, mutation in biology means "heritable alteration >of the genes or chromosomes" (unless they've gone and >changed the definition since I last looked - which is >actually possible; names of bacteria certainly are >changed with distressing frequency!). > >And while about 94% of Down's Syndrome patients do >have 47 chromosomes (the third copy of #21), in some >the genetic material of chromosome 21 is >'translocated' (attached) to another chromosome, like >#14, so technically the affected person has the >correct complement of 46 - even though one of the 14s >will be much bigger than it's supposed to be. Still >others are "mosaics," having partial trisomy - some >cells have 46, others 47 chromosomes; some mosaics >will have little outward sign of disease, having >average intelligence and height and nearly normal >facial features. ><nitpick> > Whom are you preaching to? Besides the list-resident trickster, spaceship pilot, timeline maniac, and a honoured member of Brin's Legions of Terror, I spare some time to raise a daughter with Down Syndrome :-)
BTW, the difference between mosaics and non-downs is much bigger than the difference between mosaics and 100% trisomies. The reason is not clear, but _maybe_ the mosaics are handicapped for not being recognized in earlier stages. The key point is that babies with Down Syndrome must undergo an _Early Intervention_ as young as possible. >I have a friend who is a mosaic Turner's Syndrome, who >has completed post-doctoral work and is quite >successful (full Turner's patients have only 1 X >chromosome, with various physical and mental >deficits). > IIRC, Turner Syndrome has a little impact on intelligence Alberto Monteiro _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
