The LaPerm Gene
The symbol for the LaPerm gene is Lp. Dominant genes are always written with a capital letter and recessive genes with a small letter. So the straight hair gene that pairs with the LaPerm gene is written as lp.
A normal cat would have a pair of genes for straight hair, so it’s genotype would be lplp. Although we cannot see the difference we do have two different types of LaPerm: the homozygous and the heterozygous LaPerm. The homozygous LaPerm’s gene pair consists of two LaPerm genes (LpLp), while the heterozygous LaPerm’s gene pair consists of a LaPerm gene and a straight hair gene (Lplp).
When a cat breeds it is a bit like tossing a coin. Just as a coin has two sides so does a gene pair have two genes and either one could be passed on. One parent randomly donates just one gene from its pair and the other parent donates another to make a new pair.
If one parent is a homozygous LaPerm (LpLp), then it only has LaPerm genes to offer and can only produce curly coated kittens. This makes breeding with homozygous LaPerms nicely predictable. However many LaPerms are heterozygous (Lplp) so they could either pass on a Lp (curly) or lp (straight) gene. When both parents are heterozygous then there is a chance that both could pass on the straight gene and a Variant would result.
If we go back to the coin then take two coins and imagine that heads in the LaPerm gene and tails is the straight hair gene. Toss both the coins and most of the time you will get at least one heads, sometimes two. These would all the LaPerm kittens. But sometimes you would throw a pair of tails and this would be like a straight coated Variant. Toss them enough times to get an average and you will see that there is a 25% chance of a Variant. That means one in the average litter if both parents carry straight hair.
Because a homozygous cat is like a coin with heads on both sides you will always get curly coated kittens, even when bred to a straight coated cat.
If that straight coated cat is paired with a heterozygous LaPerm (Lplp) then the kittens’ coats depend purely on that 50/50 chance of whether the kittens inherit the LaPerm parent’s curly (Lp) or straight (lp) gene.
It is a random process so the numbers do not always behave! So it is always exciting waiting to see what a mum-to-be will produce.
The LaPerm gene is unique and is the only rex gene which acts in this way to produce curly coats. Devon and Cornish Rex genes are recessive, and the dominant rex gene of the Selkirk Rex behaves in a slightly different way as it has an additive effect when the cats have a homozygous pair. What we have in our cats is something extraordinary and exceptional which we all take joy in preserving.
The special gene which makes the LaPerm unique first reared its head with the appearance of the mother of all LaPerms; Linda Koehl’s cat Curly. Curly’s mother Speedy was a normal straight coated Domestic Shorthair so we know that Curly did not inherit the gene from her mother. Although it’s possible that Curly’s unknown father was a curly coated cat, Linda and Dick never saw one on their farm before Curly and there were no other reports of curly coated kittens being sired, so it is more likely that the original spontaneous mutation happened with Curly.
Every time a new life is created the DNA, or building code, is copied, and every once in a while a little error is made as it is copied causing a spontaneous mutation. This had a happy outcome in Curly’s case altering one of her normal genes for straight hair into a gene for curly hair. With all rex breeds the hair follicles in the skin are altered to an oval shape instead of a round shape so that when the hair grows it does not grow in a straight line. It is a subtle difference which has a very obvious and noticeable effect.
The LaPerm gene is different from the rex genes which had appeared before it because it is a dominant gene. All genes come in pairs and like a game of “Scissors, Paper, Stone” if the pair does not match then one will win over the other. With the LaPerm gene curly hair wins over straight hair.