AVIAN GENETICS
PREDICTION METHODS
There are three standard methods for predicting the offspring of a particular breeding cross. These methods are the Punnett square, the Branching system and the FOIL method. The Bird Tracker Genetic Prediction Screen will perform genetic prediction tasks for you. The information on these three methods is provided merely to show how genetic crosses can be performed on paper.
The Punnett square method simply involves lining up the gametes of one parent along the top of a checkerboard and the gametes of the other parent along the side, then showing the combinations within the cross-blocks. See Figure 3 below.
The Punnett square can be expanded to solve for more than a single trait (see Figure 15) however, this method becomes very cumbersome when dealing with more than two different traits.
The Branching System method involves taking one set of parental genes and combining each of these genes with both genes of the other parental set. Figure 4 shows how the Branching system is applied to a genetic cross.
This method is very versatile (see Figure 17) and the method of choice for solving and displaying the more complex breeding crosses.
The FOIL method comes from the algebraic expression (a + b) (c + d) = ac + ad + bc + bd. This method, when applied to genetics, involves four steps as follows:
1. Combine the (F)-first of each pair.
2. Combine the (O)-outer of each pair.
3. Combine the (I)-inner of each pair.
4. Combine the (L)-last of each pair.
Figure 5 shows how the FOIL method is applied to a genetic cross.
The FOIL method is easy to use, but from a presentation standpoint does not lend itself very well to showing the sequence for how the outcome was derived. This method is pretty much done in your head. It can only be applied to a cross involving a single pair of alleles. If this method is used for crosses involving more than one trait then the individual gene pairs of the first cross need to be combined with the individual gene pairs of the second cross to show all possible outcomes. See Figure 6.
You can also derive the offspring probability by multiplying the first cross fraction with the second cross fraction as you combine the gene pairs. See Figure 7.
