Overview of Winter White Genetics
The genetics in the Winter Whites is quite easy.  There are only three genes.  The color gene is recessive and the two pattern genes are dominant (same as in the Campbells).  So sapphire is recessive while both pearl and imperial are dominant.  There is of course also the normal agouti color which is just referred to as the normal and is the color of the animal in the wild.

In many ways, the dominant genes are easier to work with than the recessive genes.  You only need one parent to have that gene present to produce babies with that pattern.  Let's take an example.  Suppose you have a pearl dwarf.  You want to mate her to a sapphire even though no other hamster in his line has been pearl.  Since pearl is dominant, you will still get approximately one half pearl babies from this pairing.

Because sapphire is recessive, though, the opposite is not true.  If you have a sapphire who you want to mate to a pearl with no sapphire in her line (i.e. none of her ancestors were sapphire), you will not get any sapphire babies.  All babies will carry sapphire but will not themselves have the sapphire coat color.  If you then breed two of these babies which carry sapphire, approximately 25% of your babies will be sapphire.  You can raise your chances by breeding a sapphire daughter back to her father.  In this circumstance, approximately one half of their babies will be sapphire.  So getting babies who show the gene with a dominant gene will usually happen in the first pairing while getting babies who show a recessive gene usually requires two pairings if you do not have two hamsters of that color.

There are a couple of other things to mention with the winter whites.  First, many pearl males are sterile.  Lately some lines with fertile males have shown up so this is not always true anymore.  As shown above, having infertile males is not a problem since pearl is dominant.  Even if only the female is pearl, you can still get about half pearl babies out of a pearl to non-pearl pairing.

Also, the imperial gene is homozygous lethal.  No defective babies are actually born, though.  Any babies which would have received two imperial genes (one from each parent or about 25% of the litter) will die in the womb and not be born.  This is not generally considered a problem since it is believed that this may actually aid the mother both by decreasing the litter size and by giving her added protein and nutrition during pregnancy.  Update:  The imperial winter white gene mutation is now believed extinct.

The winter whites can interbreed with the Campbells, and the resulting pups are called "hybrids."  Please never do this.  Also never breed known hybrids.  This will endanger both species.  There are actually countries and regions now where there are virtually no known pure winter whites.  All have been crossed into the Campbells lines sometimes out of ignorance and sometimes to get the Campbells colors into the winter whites.  These will never be pure.  There are fewer winter white colors than Campbells colors although more mutations will occur with time.  If the mutations occur within a hybrid line, though, they will never be recognized by show breeders.  So always house and breed the two species separately. 
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