 |
 Cat Breeds - There are a variety of different cat breeds. Read about the many domestic cat breeds, including the Maine Coon and Siamese cats. And view the many cat breeds pictures to see how each breed differs dramatically in coat length and overall look.
 Cat Pictures Breeds - Looking for cat pictures? Breeds pictures on every imaginable different purebred cat and kitten breed. You'll find cat and kitten breed photos in this cat pictures breeds gallery.
|
|
|
|
|
Calico Cats. Calico persian cats are almost always female. Learn why there are so few male calico cats and look at some of the beautiful calico cats pictures.
|
CAILICO CATS
Calico cats, with their orange, black and white colouration, are
almost always female. So are black and orange tortoiseshells. Why?
The answer has to do with genetics. Every cat has 38 pairs of
chromosomes; half of the pairs are from the mother, the other half
is from the father. Within every chromosome there are thousands of
different genes.
Every female cat receives one X chromosome from her mother and one X
chromosome from her father, while a male receives one X chromosome
from his mother and one Y chromosome from his father. Within the X
chromosome is a gene for coat color.
In calicos and tortoiseshells, one X has the black gene; the other X
has the orange gene. White coat color is associated with a
completely separate gene.
It's Difficult to Breed Calicos
It is difficult to breed specifically for calico or tortoiseshell
cats. Breeding an orange cat to a black cat may increase the
chances, but it all depends on whether the kitten is female and at
what stage during development the X-chromosome becomes inactive.
There is no way to predict or force an X chromosome to inactivate at
a certain point in development.
At conception, the kitten is a one-celled organism, which divides
until there are millions of cells that make up the final kitten.
Each time a cell divides, it passes on its genetic material.
|
|
|
|
|
|
Gene Inactivation
For the sex chromosomes, there is a battle for power. This is
especially true for the X chromosome.
If two X chromosomes are
present, which determines female sex, one X chromosome will become
inactivated at some point in fetal development. When this happens,
all the cells descended from the activated X chromosome will have
the same characteristics, including coat color.
In calicos, if the X-chromosome that is left functioning carries the
orange gene, then all the cells descended from it will result in an
orange color.
The same is true if the functioning X chromosome has
the black gene. If both X-chromosomes carry the same color gene,
then the calico pattern will not appear.
Since X chromosomes inactivate at various times in each individual
cat, color patches vary.
The story is different for male cats. Males have only one X
chromosome, and it is never inactivated. Whatever color gene is
present on this X chromosome will determine the color of the cat.
Males can be calico or tortoiseshell only if they are born with 2
X-chromosomes and a Y (XXY), allowing one X to be inactivated. This
genetic defect (XXY) is very rare.
|
|
Cat Homepage
Back
Site Contents Map
Page Index A-Z
