Corn Snake Genetics & Colour Morphs
The standard wild corn snake is classed as a "normal", of which there are several different shades of colour, based on the locality origin of the snake. Due to breeding projects over the last twenty years, corn snake genetics have been altered to give the snake consumer a wide variety of different colours. Through careful breeding across generations, we have breeding stock which can produce over 50 different varieties that change in value as much as looks. A famous corn snake breeder in the states retails high end morphs at as much as $1000-1500 for a hatchling that no one else is producing.
The Very Basics
There are two forms of "albino" corn snake, one lacking in black pigment - amelanistic - and the other lacking in red pigment - anerythistic. The first is often a bright orange in colour, whilst the second is black/steel grey. Hypomelanistic is when the black pigmentation is reduced, resulting in a brighter snake.
If we delve deeper into the genetics of these first two branches, you move onto the "snow" a combination of amelanistic and anerythistic, lacking in red completely, giving a very pale yellow / white snake, and the "ghost", a combination of anerythistic and hypomelanistic, which is very similar to the anerythistic, but is a slightly more shiny "silver" colour, and lacks the complete black blocks that you can find in the anerythistic variety.
The above five are the most common varieties after the normal phase.
Building Blocks
If we call the basic single gene colours building blocks (so far covered, amel, anery and hypo), then we can also add bloodred, caramel, and lavender - 2 more single gene colours that can be combined with others.
Not only do we see double gene snakes (such as snow, ghost, butter, opal, and more) but it is even possible to get triple, or quadruple trait corn snakes. These are rare, and very hard to produce.
In addition to the colour genes, you now also have pattern genetics. Corn snakes are available in standard saddles, motley pattern (rounded saddles, brighter colours, and lack of chequers on the belly) and a striped pattern. Selectively breeding striped patterns have resulted in the addition of the Cube corn snake.
If you imagine all of the colour combinations, and all of the pattern combinations - the possibilities are endless.
Visual and Hidden
All of the above morphs refer to the main colour of the corn snake, but in reality, corn snakes are far more complicated than that. There are two strings in which the colour genetics are held. One is stronger than the other, and the stronger gene dictates the colour of the snakes scales. This is called the homozygous gene, and is considered the dominant gene. When buying a corn snake from a breeder, you may see references to heterozygous colours. The heterzygous genetics refers to the "hidden" gene passed down from the parentage of the snake. For example, if you combined a normal corn snake, with an amelenistic (albino) corn snake, your offspring would be a normal heterzygous (or het for short) for amelenistic. This is because normal is the dominant colour. If you bred two "normal het amel" snakes, despite them both looking normal, 25% of the offspring would receive the amelenistic genes from both parents. In these 25% amel would then become the homozygous and the snakes would look like an albino! If you do not want to breed your corn snake ever, ignore the heterzygous nature, as it will never become relevant to you.
We have only covered some basics here of genetics.
For a fully comprehensive genetic guide including full colour photographs of all the current morphs, please visit Ians Vivarium - an excellent resource!
The corn snake manual by Kathy Love is a good instructive piece of reading material and can be bought at reptile shops, or book shops.