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Reproduction and
Genetics
Cats are seasonally polyestrous, which means they
may have many heat periods over the course of a
year. A heat period lasts about 4 to 7 days if the
female is bred; if she is not, the heat period
lasts longer and recurs at regular intervals.
The male cat's penis has spines which point
backwards. Upon removal of the penis, the spines
rake the walls of the female's vagina. The female
needs this stimulation for ovulation to begin.
Because of this, females are rarely impregnated by
the first male with which they mate. Furthermore,
cats are super fecund; that is, a female may mate
with more than one male when she is in heat,
meaning different kittens in a litter may have
different fathers.
The gestation period for cats is approximately 60
days. The size of a litter averages three to five
kittens. Kittens are weaned at between six and
seven weeks, and cats normally reach sexual
maturity at six months (females) to seven months
(males).
Blue-eyed cats with white fur have a higher
genetic incidence of deafness.
Completely white cats (not due to albinism, but
white because of the dominant epistatic white (W)
gene) with two blue eyes have a forty percent
probability of being born deaf.
The deafness is an effect of the W gene. This gene
produces a white coat because it completely masks
any other color or pattern the cat has. Blue
irises can result, and they are linked to
deafness. [16] Any cat that receives even one W
from one parent may exhibit this. Blue eyes can
also result from the form of albinism
characteristic of the Siamese breed; white cats
from this genetic background, sometimes called
Foreign whites or Oriental Shorthairs may not have
a problem with deafness, but it can happen if the
cat inherits the W gene. This also occurs with
dogs if they have white coat and blue eyes, and in
the case of dogs, it can be equally common for
them to be born blind. [17] However, blindness in
cats has not found to be associated with the W
gene. [18] Often, blue eyes will lack a tapetum
lucidum and thus will not reflect like colored cat
eyes. This may diminish the cats' visual acuity,
but the extent is not known. Humans with common
albinism, white skin and blue eyes generally
suffer from visual problems, but in Tietz syndrome
they suffer from deafness.
Around 5% of all cats are completely white, of
which 10%–20% are deaf. Very few survive in the
wild because of all the hazards that they cannot
avoid as easily as other cats would in the same
situation. Many people believe that deaf white
cats should not be used for breeding as it is not
ethical to propagate such a disability, and
instead deaf cats should be spayed or neutered to
avoid passing the trait to their offspring. [19]
Some breeds however, such as the Turkish Angora
are based on all white cats and produce a higher
percentage of deaf cats as a results. It was not
until recently that colored Turkish Angoras were
allowed to be shown, making deafness an issue in
that breed. |
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