DEAR PROFESSOR STRAIN... del1)

From: eiriasverchjanis@hotmail.com
To: strain@lsu.edu
Subject: RE: question on merle gene
Date: Mon, 17 Oct 2011 20:20:38 +0200
Dear Prof. Strain,
Thanks for your kind reply. The merle gene and its effects baffle me and I keep feeling that there is something here which I haven´t grasped. To begin with - I´m not a breeder, am not particularly a fan of conformation breeding or showing, and I´m not out to defend or denounce a gene or a coat colour. I own Rough Collies and take an interest in the various Collie breeds. In order to look at related dogs, I went to Wales some ten years ago and was delighted with the Welsh Sheepdogs - extremely intelligent working herding dogs, never bred for looks but always for practical function, many working half-wild sheep in rough country... and some of them were merles. To me, it would seem that there cannot be a loss of visual acuity or hearing of any importance in them. Also, I´ve seen skilled agility Collies here, and the same applies: unilateral loss of hearing possible, bilateral deafness not, and loss of vision not possible.
I have read claims from Catahoula breeders that merles and even double merles in their breed function and that some double merles are "heavily pigmented". My question is basically - How is it possible to be a double merle and heavily pigmented? How is it possible for double (homozygotous) merles NOT to be impaired in retinal and cochlear cell function?

I am aware of the 2006 finding of the SINE affecting the SILV (or PMel17)gene and the loss of the polyA tail in a number of melanoblasts/melanocytes migrating from the neural crest, resulting in an unpredictable "splotchiness" of dark pigment. In your opinion, is the presence or absence of hearing and/or vision explainable by this knowledge alone?
Or is it possible that there is some other factor at work here, which somehow modifies the effects of the SINE - possibly by causing a very substantial fraction of the polyA tails to drop off and so making the SILV gene  revert to functional pigment production? Would this be how some merles (and, if statements are accurate) even some double merles come to be visibly "heavily pigmented" or at least intact in retina and cochlea? Or the presence or absence of alleles on the S locus for whiteness?

I do understand that the SINE is a sinister and potentially devastating change in the SILV gene. What I don´t understand is why it is not more so, not always so, or more predicatbly so. Can you help?

Regards,
Bodil Carlsson

George Strain är professor i neurovetenskap vid Louisina State University och har sysslat i många år med bl a dövhet hos hundar. Prof Strain är en av författarna till studien av 153 hundar och sambandet mellan deras färg och deras hörsel som nämnts tidigare. Mejldiskussionen publiceras här med hans medgivande.