Sunday 29 January 2012

Cat White Spotting Gene

The cat white spotting gene is also called the piebald gene and it is not limited to cats i.e. it is the "white spotting gene". The piebald horse or painted horse is perhaps the classic example of its effect. These are bicolor horses and the bicolor cat is a very well known cat. The calico cat also carries the white spotting gene.

The white spotting gene works with any color so you will see black and white cats, tuxedo cats, calico cats (white, orange and black), tabby and white cats, grey and white cats etc. All of then carry the white spotting gene. Solid and white cats are bicolor.

The amount of white fur is very variable. The tuxedo black and white cat has a limited amount of white fur on the chest and lower limbs, while the Turkish Van is almost all white with the classic inverted "V" on the forehead and around the ears and a pigmented tail.

Sarah Hartwell kindly licensed her diagram of the various levels of expression of the piebald white spotting gene:

The "grading" of the degree of white is as follows: the more white the higher the grading. So the Turkish Van has high grade spotting. The tuxedo cat has low grade spotting.

Medium grade spotting refers to a body that is 40-60% white.

The genetic symbol for the white spotting gene is S. It is semi-dominant in its operation.
  • Ss - one dominant and one recessive allele -  white spotted cats that are heterozygotes. These are low grade and some medium grade white spotted cats.
  • All high grade spotted cats are homozygotes SS.
It is thought that the gene causes a defect in the migration of the embryonic cells called melanocytes. These cells produce the melanin pigmentation that colors hair strands. The cells fail to migrate properly to their usual positions during embryonic development and so the pigmentation for the hair strands is not formed resulting in white fur at these positions.

Top picture (copyright Helmi Flick) shows a Turkish Van high grade white spotting and the lower picture shows a low grade white spotting black and white random bred cat (a pretty and healthy looking cat). See also the piebald gene - the same gene.

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