I'm no expert, but it seems to me ...

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Posted by patricia sherman on August 10, 2002 at 01:02:11:

In Reply to: Are you sure about the bug-eyed thing?..... posted by chrish on August 09, 2002 at 12:59:34:

If it isn't a simple mendelian recessive, then it shouldn't be expressed as an "all or nothing" trait. When a defect is of polymorphic genetic composition, it is usually seen in varying degrees among the individuals within a population. If your theory is correct, then one should expect every leucistic to be a carrier, and to produce a percentage of defective progeny in every clutch. This isn't what we see happening. Dwight's example may be only of a limited number of foundation animals, but I do believe the conclusions he's drawn from what has appeared in this year's hatch are valid.

The association of bug-eyedness with leucism, may simply be coincidental. The first leucistic may have been (probably was) a carrier. Hence, 50% of the progeny of that ancestor would have been carriers. By outbreeding the descendants, we perpetuate the hidden passage of the gene through several generations, and it may be done without it appearing in any of the progeny provided each of those offspring is mated to a non-carrier; however, it will show up in 25% of the progeny of a clutch derived from two carriers. One sure way of proving whether or not this is so, would be to take a pair snakes that express normal-coloured phenotype, but are known to be of leucistic genotype, and that the leucy parent is bug-eyed. By mating these two, one should theoretically produce 25% bug-eyed offspring, and that trait should show up independent of the colour of the baby. This probably hasn't been done, and probably won't be done, for the simple reason that there's very limited demand for normal-coloured Texas rat snakes.

It may be that it does occur in normal-coloured specimens, but isn't noticed simply because the eyes are a less outstanding feature of the normals. With the leucies, the eye stands out like a beacon. If it is too large, we can't fail to see it. But a too-large eye on a blackish or dark brown or dark grey background, simply blends in, and we don't perceive it because we aren't looking for it.

Tricia

Follow Ups:

a few more notes... Dwight Good 08/10/02 (2)
- Re: a few more notes... patricia sherman 08/10/02 (1)
  - Another thought ... patricia sherman 08/10/02 (0)