Page 12 - The Complete Cat Breed Book (DK)

10 INTR ODUC TION T O C A T S

The founder effect A CAT WITH
Domestic cats spread around the world from Egypt, traveling MANY TOES
Cats with extra toes
with humans along trade routes on land and also aboard ships
are called polydactyl
sailing to newly discovered lands, such as the Americas. These cats. Polydactyl cats
cats soon established isolated populations in new locations. are common in
If any of the pioneer cats in an area possessed an unusual breeds and
populations along
trait, that characteristic stood a good chance of becoming
the East Coast.
common in future generations. In larger populations of
mixed cats, these traits would usually disappear, especially
if they caused disease or a disadvantage.
The genetic influence of these pioneering cats is known as a trait to appear, the gene is called “recessive“—the gene for
the founder effect, and it explains why certain unusual traits a longhaired coat is recessive. If a cat has both a dominant
still persist in some regions today. The best-known examples shorthair gene and a recessive longhair gene, the recessive
of the founder effect are the taillessness seen in the Manx longhair gene is masked. The cat will be a shorthair—there is
cats of the Isle of Man and the polydactylism (a genetic no intermediate effect (i.e., mid-length hair).
mutation producing extra toes) that is common in cats Sometimes genes mutate—their structure changes—and
along the East Coast of the US. they produce a different trait. Some of these mutations
can then be passed down to future generations. By using
cats with desirable genetic mutations, breeders can create
new breeds of cats—for example, with curly hair. However,
many serious diseases are also caused by genetic
mutation, and focusing on breeding within a very narrow
gene pool to promote specific traits can result in the
appearance of new diseases and disorders (pp.244–5).

DOMINANT AND RECESSIVE GENES
Cats with dark coats have at least one copy of the dominant
dense pigment gene “D,” which produces hair packed with pigment.
The recessive type of this pigment gene, “d,” reduces the level of
pigment, diluting the color of the cat’s fur. So, for example, if two
COAT LENGTH AND GENETICS black-coated cats (both with two copies of the black-coat gene “B”)
The length of a cat’s coat is controlled by a gene—the most common each have one copy of the dense (D) pigment gene and one of the
type produces a short coat. This is dominant over the type that diluted (d) pigment gene, there is a one-in-four chance that they
creates a long coat, so if a cat has a copy of each it will be shorthaired. could produce a kitten with blue (diluted black) fur.
MOTHER (BB Dd)
Cat genetics D d
Genes carry all the information necessary for life. They
control not only the chemical processes in a cat’s body,
but also the information that dictates the cat’s physical
characteristics, such as eye color and shape, coat color, and D
coat length. Genes are found on structures called
chromosomes, which are located in the nuclei of body cells.
Domestic cats have 38 chromosomes—two sets of 19 FATHER (BB Dd) BB DD BB Dd
corresponding pairs. One set of chromosomes is inherited
from the father, and the other set from the mother. Because
there are two sets of chromosomes, a cat has two copies
d
of every gene (one from each parent), and some genes have
variants that may produce different traits or characteristics.
If just one copy of a gene is needed for a trait to appear, that BB Dd BB dd
gene is called a “dominant” gene—for example, the gene for a
tabby coat is dominant. If two copies of a gene are needed for