KaDoKits Exotics presents...
Heterozygous vs. Homozygous

The terms Heterozygous and Homozygous are related to the inheritance of
dominant genes and recessive genes.

{The following Wikipedia link gives a pretty technical description:
Try it out if you're brave!}

Here's my simplified version:

Hetero means different.
Homo means same.

{zygous has to do with the fertilized egg and the DNA package it contains....
for the purpose of trying to learn these terms in relation to cat breeding....
don't worry about it!}

I'm ONLY going to talk about dominant and recessive genes in relation to color and
pattern inheritance involved in Silver Tabby Exotic breeding.

means the cat has two different alleles for a gene,
one from mom and one from dad.
Shorthand notation for heterozygous is
Let's think of Fluffy again, your black Exotic girl.

Fluffy got one black allele from her mother and one black allele from her father,
making her color gene black.

IF one of her parents carries a dilute gene, and passes it on to Fluffy,
She will have one dilute gene (
d) and one non-dilute, or dense (D).
Under this circumstance,
Fluffy (
Dd) can pass on a dilute allele to her kittens and produce a dilute kitten if bred to a
male who has one or two dilute alleles.
{Remember your blue-cream kitten?}
We would say that Fluffy is heterozygous for dense color.
Her alleles for color dilution are

You'll more commonly hear people talking about an Exotic being
heterozygous for short hair, a dominant gene.
IF Fluffy has one allele for short hair from one parent and one allele for long hair (a
recessive trait) from the other parent, she is said to be
heterozygous for short hair.
Her alleles for hair length are
This means she can produce both short hair and long hair kittens,
depending on the genetic make up of her mates.


means a cat has two alleles for a gene that are the same,
one from mom and one from dad.
Shorthand notation for homozygous is
Back to Fluffy's pedigree.  

Remember, the chances of Fluffy having a dilute gene are pretty slim, since the dilute
colored cats in her pedigree appear in the 4th generation with her great-grandparents.

IF Fluffy did not receive a dilute gene from either parent,
she only has dense color to pass on to her kittens and
there will be no dilute colored kittens in her future.
We would say that Fluffy is
homozygous for dense color.
Her alleles for color dilution are the

Exotic breeders also longingly talk about an Exotic being
homozygous for short hair...a dream!
IF Fluffy received only short hair alleles from her mother and her father,
{which has a 50% possibility since both parents are shorthairs and
assuming they both could carry the longhair gene},
she is said to be
homozygous for short hair.
Both of her alleles for hair length are the
This means she will only produce shorthair kittens, no matter the hair length of her mates.

It is important to remember
that ANY trait that is a result of dominant and/or recessive genes
can be talked about as heterozygous or homozygous for that trait.
 GC, Hot Diggety!, red PER
CH, Hot Dang!, red ESH
|    |
|    Blue Belles N Roses,
blue-cream ESH
GC, Cinderfella, black ESH
|    |
|    |    Burnt Offering, black ELH
|    |    |
|    GC, Fire N Ashes, tortoiseshell ESH
|         |
|         GC, Flash Dance, tortoiseshell ESH
F, GC, Fluffy, black ESH
|         GC, RW, Sir Luv-Lee-Purrz, red PER
|         |
|    GC, GP, Burnin' Luv, red PER
|    |    |
|    |    CH, Flamin' Heart, red PER
|    |
GC, Painted Lady, tortoiseshell ESH
|    GC, Blue Moon,
blue PER
|    |
CH, Midnight Kiss, black ESH
 Total Eclipse, black ESH
Copyright: Pedigrees2020© 1991-2005;//,
KaDoKits Exotics