Tabby refers to the pattern on a cat's coat and is not a breed. The name "tabby" is believed to have derived from Atabi, which is a type of striped taffeta (known as tabbi) that was manufactured in the Attabiah district of Baghdad.
The word tabby was derived from a kind of taffeta, or ribbed silk, which when calendered or what is now termed "watered", is by that process covered with wavy lines. This stuff, in bygone times was often called "tabby:" hence the cat with lines or markings on its fur was called a "tabby" cat. But it might also, one would suppose, with as much justice, be called a taffey cat, unless the calendering of "taffey" caused it to become "tabby". Certain it is that the word tabby only referred to the marking or stripes, not to the absolute colour.
Genetically all cats are tabby, however many possess "modifier" genes which inhibit this pattern from being expressed. The mackerel tabby (Mc) is the "default" (wild type) pattern, with the classic pattern being recessive (mc). Recessive genes require two copies (one from each parent) in order to be expressed. The spotted tabby is essentially a mackerel tabby with a modifier gene which breaks up the markings from stripes into spots. If cats were allowed to do their thing (so to speak), and no more selective breeding occurred, then they would eventually revert back to the default tabby pattern after a few generations. This is known as "revert to type".
The gene for the tabby pattern is known as agouti and is dominant, the "code" for this gene is A/a (a capital letter symbolises that the gene is dominant, a lower case letter means the gene is recessive). So, if a cat inherits two recessive "a" genes, then it will be a non tabby (solid) cat as the presence of the a/a masks the tabby pattern.
A/A = tabby
A/a = tabby
a/a = non tabby (solid)
The tabby comes in three main colours.
The brown tabby has darker spots and stripes on a lighter background such as black spots/stripes on a brown background.
The silver tabby has dark grey spots/stripes on a light grey background.
The red tabby has dark red spots and stripes on a light red/cream background.
Other colours include cream tabbies and blue tabbies.
There are four main tabby patterns:
Classic (also known as blotched or marbled)
Dark bold and clearly defined markings, on a lighter yellowish background. Lines, swirls and whorls which are unbroken on the top of the cat and swirled along the sides, with barring on the legs and rings around the tail.
Clearly defined, vertical stripes going around the cat's body. Mackerel stripes are narrower than those on the classic tabby. Legs have bracelets and the tail is barred.
Dark spots on a lighter background.
The ticked tabby has contrasting dark and light bands of colour on each hair.
The tabby pattern is dominant over almost all other coat patterns with exception for the white masking and white spotting genes.