Re: webbing

16 Jul 1995 20:27:03 GMT

Alex Duncan ( wrote:
: ---trimmed---
: Speaking of ANCIENT features -- any thoughts out there about the
: occassional occurence of polydactyly in humans? I've often thought that
: we all must have the genetic potential for more digits than we actually
: have. It is well known now that both Acanthostega and Icthyostega had
: more than 5 on both fore and hindlimbs. Perhaps the occassional
: appearance of extra digits in humans results from the faulty function of
: a regulatory gene.

Sure does. The fruitfly geneticists have been getting into this area for a
couple of decades, and their genes are starting to match up to those found
in vertebrates (homeobox genes in particular). For example, the vertebrate
brain seems to be segmented, with the segments matching those found in the
front end of arthropods. During development, regulatory protein gradients
are established that result in the emergence of periodic structures,
modulated by other gradients. These processes eventually set up a somatic
mapping that controls the gross positioning of cells and neuronal
connections. In the appendages, what results is a structure with five
major parallel components. In the intervening spaces, the cells initially
form a thin web, which is trimmed away in most mammals by programmed cell
death. If a given gradient is misprogrammed, you can get six or seven
components where five usually fit. Certain domestic cat breeds are
particularly prone to this.

One of my sons is working in this area. (I'm racing him to a PhD. So far,
I'm ahead.)

Harry Erwin
Home Page: (try a couple of times)
PhD student in comp neurosci: "Glitches happen" & "Meaning is emotional"