Punnett Squares
Punnett squares are used to determine the probable outcome of a cross. In english, they help to figure out what could happen when you breed two rabbits (or anything else). For example, if I have a chocolate doe that I want to breed with a black buck, what colors could I get? That's when punnett squares come in handy. The differance in black and chocolate colored rabbits is the 'b' gene. In this cross, they will both be homozygous, meaning that they have the same two genes (example: bb) Here's how it's set up:
(chocolate) bb x BB (black) -each rabbit can pass on 1 gene.
b or bxB or B
B B
b Bb Bb
b Bb Bb
All the babies are heterozygous black. Heterozygous means that they have two different genes. Black is totaly dominant, so they will all be black. They will all carry the chocolate gene. If I cross two heterozygous chocolates, one out of four will be chocolate. I'll set it up:
Bb x Bb
B or bXB or b
B b
B BB Bb
b Bb bb
There is one homozygous black, two heterozygous black, and one homozygous chocolate. Keep in mind that there might be more chocolates, or no chocolates all together! Punnett squares only determine probablility, not frecuency. They can be done with as many genes as you want! Just 'cancel' out all the homozygous pairs that are the same, and do the cross with the rest!
chocolate: aa bb CC Dd EE All the a's, c's, and e's are the same, so cancel them.
black: aa BB CC Dd EE
The cross is: bbDd x BBDd Figure out all the possible combinations, then do it!
BD BD Bd Bd
bD BbDD BbDD BbDd BbDd
bD BbDD BbDD BbDd BbDd
bd BbDd BbDd Bbdd Bbdd
bd BbDd BbDd Bbdd Bbdd 75% are black, 25% are blue.
A tip for doing punnet squares is to allways write the dominant gene first in the square, and the reccesive after it. Keep the genes in order though (ABCDE...). In this last cross, I didn't cancel the 'Dd'. That is because they arn't homozygous. If I would have canceled them out, then I wouldn't have realized that I could get blue rabbits.
Punnett squares can get a whole lot more complicated. I tried a cross once for fun that I was only able to cancel one gene pair out! It took a very long time to do. Most of the time, the more diversity in the genes, the more possible colors. The problem with this is that the colors might not be recongnized in the particular breed. That can be good or bad, depending on the goals of the breeder.
NICE WORK! You just learned the basics of color genetics! |
