Quote:
Punnett squares ( named after Reginald Punnett) is used to make predictions concerning how alleles come together to make the offspring from two parents. The Punnett square also predicts the probability of a specific phenotype ( color, ect.) being produced when an allele from the mother combines with the allele from the father.
For simplicity, lets say the extended black allele ( E) produces a black chicken; so the father will have two E alleles for extended black and be E/E. He will only give one E allele to each of his children. He has two alleles: when he makes sperm one E will go in one kind of sperm and the other E allele will go into the other kind of sperm.
If the mother has an extended black allele E and a wild type allele e+ ( she is E/e+)she can make eggs that have an extended black allele and eggs that have the wild type allele. Like the sperm, the eggs can only contain one allele either an E or an e+.
So you make a square. Fathers sperm goes on top and the mothers eggs go on the side.
E E
E | EE | EE |
e+| Ee+ | Ee+|
The sperm and egg come together in the square so half of the offspring or 1 in 2 of the offspring will be solid black or E/E the other offspring will be or 1 in 2 of the offspring will be pseudo birchen similar to a birchen bird (black with some red or white in the hackles).
Now watch what happens if you cross a male who is E/e+ with an E/e+ female. The probabilities will be different.
E e+
E | EE | Ee+ |
e+| Ee+ | e+e+|
Now the offspring are different, you get one in four that are black (E/E) , 2 in 4 that are pseudobirchen (E/e+) and 1 in 4 that are wild type (e+/e+) or recessive for a trait. You get three different colors from this cross. So if you hatch 20 birds 5 should be black , 10 will be pseudobirchen and 5 will be wild type. The numbers are probabilities which means the numbers of colors will most likely not be exactly 5 to 10 to 5. If you hatched 1000 birds then the numbers will be close to the 5 to 10 to 5 ratio or 1 to 2 to 1.
Remember when you are doing Punnett squares always use a capital letter to represent the dominant gene (E) and a lower case letter (e+) to represent the recessive gene. The plus sign indicates the gene is a wild type gene or would be found in a wild population.
The genes are actually represented in a different manner now; this is the older style of writing genes and it works best for people learning genetics. The new way of writing genes is different.
Extended black is E*E and wild type is E*N. Work on the E locus is on going so the way the genes are written may change. There is another scientific way of writing genes which is more complicated so I will not go into the newest way because you would have to have a back ground in biochemistry to really grasp the concepts.
Once you understand how to make punnett squares use the punnett monkey.
http://web.archive.org/web/20060316...tripod.com/geneticspages/Punnett_Monkey3.html
Henk,
I corrected the typo.
Tim
