From: pholland@iastate.edu (Paul J Hollander)
Subject: Re: Snake color morphs ?
Organization: Iowa State University, Ames, IA
Date: Tue, 21 Jul 1992 21:26:34 GMT

In article <119310005@hpfcso.FC.HP.COM> ruska@hpfcso.FC.HP.COM 
(Dave Ruska) writes:
>
>Anyone care to explain the following snake "color" terms? I've encountered
>these reading through various snake classifieds. 
>
>    Melanistic (king snake) ...           [ chocolate ? ]

I've never seen a chocolate.  My impression is a uniformly dark snake.
Corrections welcomed.
>
>    Amelanistic (corn snake) ...

The red color is present, the black pigment is not present.  Amelanistics have
a white edge around the dorsal blotches instead of a black edging.  They have
white mottling on the sides instead of black mottling.  Pink eyes and tongue.
The whole aspect is a little more orange than in the normal.
>
>    Anerythristic (boa) ...

All reds and yellows are gone, leaving the black pigments.  Generally 
various shades of gray.  Again, this is one I haven't seen.
>
>    Heterozygous (burm) ...

Albino, anerythristic, amelanistic and most other color and pattern mutants 
are caused by genes that are recessive to the gene for wild type (= normal 
= standard) at the same location.  Genes are paired because the chromosomes 
are paired.  Homozygous means that the pair of genes are the same.  
Heterozygous means the pair of genes are not the same.  A heterozygous 
albino Burese has one albino gene paired with a normal gene.  Because albino 
in Burmese is recessive to normal, a heterozygous albino looks normal.  You 
know it is carrying that one albino gene if 1) one parent was homozygous 
albino, or 2) it has been mated with either a heterozygous or homozygous 
albino, and one or more babies were albino.
>
>    Albino (burm) ...                      [ white ? ]

The black pigment is gone, leaving a pale yellow pattern on the snake.
>
>    Patternless Albino (burm) ...  

Sometimes called a banana Burmese.  Green (patternless) essentially produces 
a snake that's uniformly colored over the back and sides.  Albino removes
the black pigment.  The result is a uniform pale yellow snake.
>
>  Are these terms dependent on the particular (sub) species, or are they 
>  common terms for any snake ?

Homozygous and heterozygous apply to the gene arrangement in any plant or 
animal.  Albino can be applied to a particular gene (for example, *the* albino
gene in the laboratory mouse) or to any animal that looks more or less white.
There are two different types of albino in the black rat snake plus leucistic
in the Texas rat snake, a subspecies of the black rat.  All are inherited
independently, but each could be *loosely* termed albino.  The trick is to
know whether someone is speaking loosely or exactly when the same word can
be interpreted either way.  8^(

Not too many genes have been written up in the literature to nail down a
name for them.  Amelanistic and anerythristic in corns, striped in California
kings, and most of the black rat snake mutants are the exceptions.  To the
best of my knowledge, no one has written up green or albino in Burmese or most
of the California king mutants.
>
>And if you know what all those mean, then translate the following ad from NOAH:
>
> FOR SALE: Burmese pythons: Albino 50% probable hetero for green, albino,
>           hetero for albino 50% probable double hetero, hetero for albino,
>           hetero for green 50% probable double hetero. All available now....

This guy has been messing with both green (patternless) and albino.

The way to get a 50% probability for the green mutant is to mate a homozygous
normal to a heterozygous green.  Here's the Punnett square, where + means
the normal gene and gr means the green gene:

Parent 1 gametes:     |   +   |   gr  |
                    -------------------
Parent 2 gametes:   + |  ++   | +/gr  |
                    -------------------
                    + |  ++   | +/gr  |
                    -------------------

50% (allowing for experimental error) of the babies from this mating will be
homozygous normal, and the other 50% will be heterozygous for green.  But
you can't tell which is which by looking at them, only by breeding tests.
So the convention is to refer to these babies as "50% probability heterozygous
for green."  

IMHO, this ad could be garbled results from one mating of an albino that is 
homozygous for normal at the green locus with a snake that is heterozygous 
for albino and heterozygous for green (double heterozygous).  Offspring 
would in 4 categories:
1) albino and homozygous normal at the green locus.
2) albino and heterozygous for green.
3) heterozygous albino and homozygous normal at the green locus.
4) heterozygous albino and heterozygous for green.
Category 1 and 2 look identical, and category 3 and 4 look identical.

Alternatively, the baies listed in the ad are from several matings.

Paul Hollander    pholland@iastate.edu
Behold the tortoise: he makes no progress unless he sticks his neck out.