KaDoKits Exotics Genetics Punnet Square

KaDoKits Exotics presents the Punnet Square...

"A Punnet Square

is a diagram designed by Reginald Punnet and used by biologists to determine
the probability of an offspring having a particular geneotype.
It is made by comparing all possible combinations of alleles from the mother
with those from the father."
(source: Punnett square. (2007, July 23). In Wikipedia, The Free Encyclopedia. Retrieved 06:16, July 27, 2007,
from http://en.wikipedia.org/w/index.php?title=Punnett_square&oldid=146515139 )

I am going to try to offer a simple explanation of how to use the Punnet squares
in your breeding program.

Important....

In its simplest form, a Punnet Square is used for just ONE trait at a time.
It can be used for more than one trait,
as long as those traits are not dependent on each other being present.
This method is quicker, but only for those very fluent in their genetics.

Another point is that the Punnet Square is only useful for dominant/recessive traits.
It is not used for determining color inheritance because that is sex-linked.

Remember.....

The female sex cell is the ova (ovum plural).
The male sex cell is the spermatozoa (sperm plural).
These are collectively called "gametes".

When the sex cell is formed, 1/2 of the cat's DNA....1/2 of its chromosomes,
is inserted into each ova and each spermatozoa.
So, in the Punnet square below,
each colored cell, the pink A & B for the mother and the blue C & D for the father,
represents one trait that is in one sex cell.

Imagine, for every set of dominant and recessive traits, you might have strings of Punnet
Squares right along with your strings of DNA!

Conventional Notations

Dominant alleles are noted with an upper case letter, ABC.
Recessive alleles are noted with a lower case letter, abc.

People fluent in their genetics,
use the correct letter designations for each trait set up by the scientific community.
These can be found by going to one of the genetics web sites
or consulting a cat breeding genetics text.

The inner four yellow squares represent the probability or chances
the offspring from this particular mating will end up with
a particular set of genes (called genotype).

It is properly referred to as a % chance of the offspring inheriting whatever
gene combination results.
Each yellow cell equals a 25% chance.
If the same gene combination is in more than one yellow cell,
then simply add the % for each square.

Cat breeders often refer to the results in terms of a hypothetical litter of 4 kittens.
one yellow cell = 25% chance = one kitten
two yellow cells = 50% chance = two kittens
three yellow cells = 75% chance = three kittens
four yellow cells = 100% chance = four kittens

Remember, this is all hypothetical.
To get a really accurate idea of a thing's chance of occurring, you'd have to do it 100 times.
Take a penny, for example.
When you flip a penny, you have a 50% chance of having it land on heads,
and a 50% chance of it landing on tails.
Try it out for yourself....flip a penny 100 times and record your results.

That's how it is with breeding cats and trying to get a certain characteristic.
If you want to see the Punnet Square probability results actually happen,
you would have to do the same breeding enough times to produce 100 kittens!

So, don't be surprised if your breedings result in ALL of the kittens having the same characteristic,
even though your Punnet Square results say the characteristic has a 25% chance of happening!

Last thing....
Punnet Squares are not usually colored.
I just like using color to help me organize my thoughts and it is an easy way to cue different points
I'm talking about.

A Real Catty Example

I am going to use the dilute allele, a recessive trait.
It modifies dense colors, a dominant trait.

Let's say you only have dominant colored cats.
They are all out of dominant colored parents. Some of them, your male and a few queens, do have
dilute ancestors in their pedigrees.
How do we get a dilute kitten out of two dense colored cats?

Keeping it simple, lets say both mother and father are black (a "dense" color).
{red or tortie could be used as well, both dense colors}
They each carry one copy of the dilute gene, a recessive trait.
d will represent the dilute allele
D will represent dense color or non-dilute

Each parent's gene pair is Dd.
For the father, place D in the left blue cell and d in the right blue cell.
For the mother, place D in the top pink cell and d in the bottom pink cell.

The results:
25% chance of DD, or dense color with no dilute gene;
50% chance of Dd, or dense color carrying one dilute gene;
and 25% chance of dd, or dilute colored kitten(s)!!!!!!

Viola!
I love using Punnet Squares.
They're a great tool for breaking down a complicated genetic package into smaller pieces.
Besides, it's fun!

mother

father

25%

father-black, Dd

mother-
black
Dd

Figuring the offspring
Notice the yellow cells in the square to the left
are lettered w, x, y, and z.

Start with the mother.
Place the D from the top pink cell in yellow cells w & x.
Place the d from the bottom pink cell in yellow cells y & z.
Next, the father.
Place the D from the left blue cell in yellow cells w & y.
Place the d from the right blue cell in yellow cells x & z.

The Punnet square below shows the correct results.