Are bicolor cats rare, friendly, hypoallergenic?

Tuxedo cats are bicolor cats. This is my darling deceased female. Image: MikeB

Bicolor cats are cats with a coat of two (as in 'bi') colors: white and another colour such as black or ginger. And the 'other colour' can have tabby markings. 

They can be moggies (random-bred cats) or purebred, pedigree cats. It does not matter which. They are common and therefore not rare. Neither are they hypoallergenic but they are friendly if they've been socialised properly and treated well.

No domestic cat is hypoallergenic as the Fel D1 allergen is produced by all domestic cats. Purina LiveClear works pretty well to make a cat acceptable to a person allergic to cats.

'Hypoallergenic' means not producing an allergic reaction in people. About 10% of people are allergic to cats.

The white fur in bicolor cats is caused by the presence of the piebald aka white spotting gene, which affects the migration of pigment producing cells (melanocytes) in the skin during the development of the embryo. 

Where there are no melanocytes there is no melanin in the hair strands. White fur does not contain pigment namely melanin.

It is white because the light from sun or room light passes through it. White light is a mixture of all the colours of the rainbow.

Melanin is a brown/black. If it is diluted, black becomes blue grey and red becomes cream and so on.

The experts rate bicolor cats from 1 to 10 depending on the amount of white fur. Level 1 is black and no white fur while level 10 is all-white. The cat in the picture is about level 4.

If you have a question, ask in a comment and I'll be pleased to respond. I always check comments as I get so few! :)

Level 9 bicolor Cornish Rex. Image in the public domain.

Cat develops a dead straight blonde fur line on her black fur overnight. Why?

This is the question on Reddit.com: Binx has (overnight) developed a dead straight line of blonde on her back. Any ideas?

Black cat with blonde stripe on her back which developed rapidly. Image: u/FyldeCoast on Reddit.com

There is obviously no certainty that I am correct. It is a kind of guess based on little to go on. If you have a better idea please comment. It would be great if you did 😃.

RELATED: 2 examples of feline vitiligo (leukoderma).

This is my answer

It looks like it could be vitiligo. It is harmless. Antibodies attack the melanocytes (pigment producing cells in the skin in the hair follicle bulb). The melanocytes are destroyed and no longer produce melanin, a dark pigment producing black fur. This leads to fur without pigment in a localised area. The hair strands in that are just keratin and therefore semi-transparent having the appearance of being off-white. The white area may expand. Sometimes cats with vitiligo turn from black to white! Studies indicate that changes in the immune system are responsible for the condition and that both underlying genetics and environmental triggers are involved. Now you'll tell me some bleach dripped onto her back 😊.

What wild cats are black?

No wild cat species (as a species) is black. Sometimes individual wild cats of some species are black or dark charcoal because of a genetic mutation resulting in melanism. The classic melanistic wild cat is the black jaguar called the black panther. The puma can be black too and so can the bobcat, the serval, the leopard and Geoffroy's cat. These names come out of my head. I have probably forgotten some.

Black leopard (melanistic). Pic: Pixabay.

But the point is that the answer is NONE. It is just that some individuals do end up black against the usual colour of the species concerned because of this genetic mutation.

SEE SOME BLACK PANTHER PICTURES.

Melanism affects many animals of many species, not just some wild cats. For instance melanistic leopards are quite common. They are sometimes bred in zoos. Black leopards are caused by a recessive gene. They are less fertile than normal leopards according to Sarah Hartwell, a cat genetics expert.

Black leopards in captivity may be more highly strung than normal leopards because they are bred to entertain the public and in doing that they become inbred. This affects their mental health. 

As leopards are nocturnal being black does not impede hunting but probably has the opposite effect. Melanistic leopards are also called black panthers.

Are hairless cats really hairless?

No, so-called "hairless cats" are not truly hairless because various parts of their bodies maybe nude but the remainder e.g. the muzzle and the feet (often) are covered by fine down, fuzzy hair. Sometimes hairlessness progresses with age. There is a fine covering in the young adult cat which gradually disappears leaving a bare, wrinkled skin over much of the body of the full-grown adults.

Bicolor Sphynx. The fine down hair strands in the hind legs are
pigmented I believe, which is why there is a dark patch and the tail
 is dark too. This is melanin in the down hair strands.

There is a bit of discussion about whether hairless cats can have a pattern on their skin. You do see 'bicolour' Sphynx cats with the two colours being the skin colour and the other colour being an inky darker colour. 

I had thought that the darker coloration was due to the pigment producing cells, the melanocytes, colouring the skin but I now believe that this is due to fine down hairs having the coloration that the cat's genetics gives it. The melanin in the hair strands being produced by the melanocytes.

To be clear, if you see a bicolour Sphynx or any other hairless cat what you are seeing is hair strand coloration. The point is that you can barely see the hairs because they are very fine and short, being the down or undercoat.