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Sex Linked Genetic Traits

I am going to talk only about color inheritance here
since that is the major sex linked trait we are all interested in.


In cats, the allele for color (black or red),
is found on the sex chromosomes, specifically the X chromosome.

Female cats have 2
X chromosomes, one from each parent.
This is noted like this:
X X

Male cats have 1 X chromosome and 1 Y chromosome,
one from each parent.
This is noted like this:
X Y

{If you do a Google Image search,
you can find pictures of actual cat chromosomes and will see that
the Y chromosome is smaller than the X chromosome.}


Once upon a time, a long time ago, in a land very far from here...
I asked one of my college biology professors why color inheritance worked the way it did.  
He said the location (locus) of the color allele
was on the area of the chromosome that is missing on the Y chromosome.
I don't know if this is accurate,
but it is a plausible explanation as to why the color allele is only found on the X chromosomes.
How It Works

Remember, there are only two basic colors....black and red.
Tortoiseshell is a combination of black and red.
The dilute colors occur because the recessive dilute gene modifies these dense colors.


Mothers....control everything!

A black female offers black on both X chromosomes:  X  X
A red female offers red on both X chromosomes:  X  X
A tortoiseshell female offers black on one X chromosome and red on the other:  X  X

Mothers have a say in what the color is going to be in BOTH her sons and daughters.
This is why I always start with the mom's color.

Fathers....control some things.

A black male offers black on his X chromosome:  X
A red male offers red on his X chromosome:  X
All males also offer a Y chromosome.

Fathers determine the gender of the kittens.
Since mom is giving both sons & daughters an X chromosome, dad gives either the X or the Y.
The kittens who get the X from dad are the daughters.
The kittens who get the Y from the dad are the sons.

This is why we say the father determines the color of the daughters (along with mom!).
And the mother (only) determines the color of the sons.
Some Examples

When figuring colors,
I use a hypothetical litter of 4 kittens, 2 males and 2 females.
I have mom give one
X to Son A and the other X to Son B.
I also have her give one
X to Daughter A and the other X to Daughter B.
Then, I have dad give his
X to Daughter A and his Y to Son A.
Additionally, dad gives his
X to Daughter B and his Y to Son B.
This allows us to see all color combinations possible for sons and daughters.

Black Female
black X
black X




















Red Female
red X
red X




















Tortoiseshell Female
black X
red X




























NOTE:  If you have the dilute gene on both sides (mom & dad), either a dilute or a dense color that
carries dilute, you can add to your possibilities blue where ever there is black;
cream where ever there is red; and blue-cream where ever there is tortoiseshell.  
If both parents are dilute, you will not get dense colored kittens.
Bred to a Black Male
black X
Y











from this breeding,
sons will be black
daughters will be black
Son A
Son B

mom's
black X

dad's
Y
Daughter A
Daughter B

mom's
black X

dad's
black X
Bred to a Red Male
red X
Y











from this breeding,
sons will be black
daughters will be tortoiseshell
Son A
Son B

mom's
black X

dad's
Y
Daughter A
Daughter B

mom's
black X

dad's
red X
Bred to a Black Male
black X
Y











from this breeding,
sons will be red
daughters will be tortoiseshell
Bred to a Black Male
black X
Y


















from this breeding,
sons will be black or red
daughters will be black
or tortoiseshell
Son A
Son B

mom's
red X

dad's
Y
Son A

mom's
black X

dad's
Y

Son B

mom's
red X

dad's
Y
Daughter A
Daughter B

mom's
red X

dad's
Y
Daughter A

mom's
black X

dad's
black X

Daughter B

mom's
red X

dad's
black X
Bred to a Red Male
red X
Y











from this breeding,
sons will be red
daughters will be red
Bred to a Red Male
red X
Y


















from this breeding,
sons will be black or red
daughters will be red
or tortoiseshell
Son A
Son B

mom's
red X

dad's
Y
Son A

mom's
black X

dad's
Y

Son B

mom's
red X

dad's
Y
Daughter A
Daughter B

mom's
red X

dad's
Y
Daughter A

mom's
black X

dad's
red X

Daughter B

mom's
red X

dad's
red X
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