wijsman at max.u.washington.edu wijsman at max.u.washington.edu
Wed Oct 23 23:52:54 EST 1991

>From: stormo at boulder.Colorado.EDU (Gary Stormo)
>Subject:evolution and speciation
>Date: 23 Oct 91 20:37:31 GMT

>Some time ago there was a discussion about the definition of evolution.
>While a consensus did not emerge there was considerable support for any
>change in allelic frequencies.  There have also been discussions of the
>mechanisms of speciation and how that fits within evolution.  A common
>conception is to equate speciation with macro-evolution, arising when
>"sufficient" micro-evolutionary events (allelic changes) have occured 
>that two organisms can no longer mate productively.  While this may be
>the normal situation, it occured to me that it need not be that way.
>While daydreaming during a recent meeting the following experiment
>occured to me (perhaps this has been done, anyone know?).  
>Given the large number of chromosome translocations and inversions
>that exist in Drosphilia, one ought to be able to construct some flies
>whose offspring are competent to mate with each other (or at least a 
>subset of their sibs) but would have very low fertility in matings to
>any other strains, even the parental.  If so, these would represent a
>new species, by the usual definition, in which there has been no change
>in allelic frequencies (at the gene level, I'm not counting a rearranged
>chromosome as a new "allele").  

Yes, it is possible to construct such flies.  There are, for example,
strains of Drosophila with drastically rearranged chromosomes, such as
one chromosome with two chromosome 2 long arms on either side of the
centromere, and another chromosome with two chromosome 2 short arms
on either side of the centromere.  Such strains breed true and cannot
produce viable offspring in matings with "normal" Drosophila.

Ellen Wijsman
Div. Medical Genetics, RG-25
Univ. of Washington
Seattle, WA   98195
wijsman at saam.bioeng.washington.edu

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