HOW TO WORK OUT THE RESULTS OF A BREEDING
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This section assumes basic knowledge of the meaning of the terms 'Phenotype' and 'Genotype', 'Homozygous' and 'Heterozygous', 'Dominant and 'Recessive'. It also assumes some basic knowledge of how genes are passed from parent to child, so if you are a complete beginner, please at least read 'The Basics' section first. A knowledge of the dominant/recessive relationships and abbreviations of the different genes is also necessary, so these examples are designed to be used in conjunction with the 'Overview of the different genes used' section.
The easiest way to calculate the results of matings is to use a 'Punnet Square' (P-square) (follow this link for more information). The basic P-square looks like a window:
Given enough information about two cats to be bred, we can use this square to work out the genotypes and phenotypes (see 'The Basics' section) of the resulting offspring.
The Steps to follow:-
Step 1: Determine the genotypes of the cats to be bred.
Step 2: Write down those of interest.
Step 3: Draw an appropriate P-Square.
Step 4: 'Split' the letters of the genotype for each cat and put them on the 'outside' of the P-Square.
Step 5: Fill in the P-Square to determine the possible genotypes of the offspring.
Step 6: Summarise the results as required.
Using the process:-
For this example I will use a mating between a Longhaired male and a Shorthaired female whose Sire was Longhaired. I will assume that the only thing we are interested in is the hair length of the offspring.
Step1: Determine the genotypes of the parents
The longhaired gene is recessive, so a cat with a longhair phenotype must be heterozygous for longhair. This means that we know that the male is 'll'. The phenotype of the female could either be 'LL' (homozygous shorthair) or 'Ll' (heterozygous shorthair). However, her Sire must have been 'll' (he was longhaired), so she must have received a 'l' gene from him. This means that she must be carrying longhair, so is heterozygous for shorthair 'Ll'.
Step 2: Write the genes in the correct form
Step 3: Draw an appropriate P-Square
Step 4: 'Split' the genotype and write the letters on the outside of the P-Square
Take the first parent (in this case the male), and put his letters against the top of the P-Square. He is an 'll' so we put an 'l' against the first column and an 'l' against the second column:
Take the second parent (in this case the female), and put her letters against the left side of the P-Square. She is an 'Ll' so we put an 'L' against the first row and an 'l' against the second row:
l l L l
You are now ready to calculate the potential genotypes of the offspring!
Step 5: Fill in the P-Square
To calculate the genotypes of the offspring, you draw down the letter from above each column, and the letter from beside each row (always putting the dominant letter first), to fill in each box in the P-Square. In this case, for the first box, we have an 'l' from the top of the column and an 'L' from beside the row. The 'L' is dominant so we put it first:
l l L Ll l
For the second box in the first row, we take the 'l' from above the column and the 'L' from beside the row. Again, the 'L' is dominant so we put it first:
l l L Ll Ll l
Follow the same procedure to fill in the second row ('l' from above and 'l' from beside in both cases):
l l L Ll Ll l ll ll
This gives us our completed genotype profile for the results of the mating.
Step 6: Summarise the results as required
Row 1, Column 1: Ll
Row 1, Column 2: Ll
Row 2, Column 1: ll
Row 2, Column 2: ll
Looking at the P-Square we can see that two of the four squares give Ll, while the other two give ll. This means two in every four kittens from this mating would be shorthair carrying longhair (Ll), and the other two in every four would be longhair. This can also be thought of as statistically ½ or 50% of the kittens from this pair.
It is always worth remembering that pf runs on computer, and therefore on statistics. If you were to do 100 matings with these same two cats, you should get roughly 50 longhair and 50 shorthair (carrying longhair) kittens. However, in any one mating you could get all longhair or all shorthair (carrying longhair), and a second mating of the same pair could produce the opposite.
A More Complex Problem:-
When completing a more complicated problem (i.e. when looking at more than one gene), we use the same principle but have more letters in each row/column. For example, assume that the male in the problem above is Dominant White whose Sire was non-white (Therefore the male is Ww), while the female is a non-white (ww). This gives us the following total genotypes:
Male: ll Ww
Female: Ll ww
For each cat, there are four possible combinations:
1st gene from the 1st pair with the 1st gene from the 2nd pair
1st gene from the 1st pair with the 2nd gene from the 2nd pair
2nd gene from the 1st pair with the 1st gene from the 2nd pair
2nd gene from the 1st pair with the 2nd gene from the 2nd pair.
For the male in this case this would be:
lW (The 1st 'l' in the pair with the 'W')
lw (The 1st 'l' in the pair with the 'w')
lW (The 2nd 'l' in the pair with the 'W')
lw (The 2nd 'l' in the pair with the 'w')
For the female in this case we have:
Lw (The 'L' with the 1st 'w' in the pair)
Lw (The 'L' with the 2nd 'w' in the pair)
lw (The 'l' with the 1st 'w' in the pair)
lw (The 'l' with the 2nd 'w' in the pair)
However, because the first pair of genes are the same for the male (both 'l'), and the second pair are the same for the female (both 'w') we have two repeats in each case. We have both lW and lw twice (once with each 'l') for the male, and both Lw and lw twice (once with each 'w') for the female. In the P-Square, each of these need only be entered once, because the results will be the same. So, in this case, starting with the 'L' in the first row:
(In more complex problems, some people prefer to colour the letter changing in each column, for ease of checking - you check that there is the correct number of coloured letter in each box. In this case, the changing letter is in red)
We move each item across in its pair, so we move the first letter in each row/colum across/down first, and then the second. Moving the hair length gene first gives us:
(Note this is the same as the previous problem where we only looked at hair length)
We then move the White gene across/down, and this gives us:
|Lw||Ll Ww||Ll ww|
|lw||ll Ww||ll ww|
Row 1, Column 1: Ll Ww
Row 1, Column 2: Ll ww
Row 2, Column 1: ll Ww
Row 2, Column 2: ll ww
25% (¼) of the litter would be Shorthair (carrying longhair) and Dominant White
25% (¼) of the litter would be Shorthair (carrying longhair) and non-white
25% (¼) of the litter would be Longhair and Dominant White
25% (¼) of the litter would be Longhair and non-white
Are you still following? If not, go back and read through this again. You could also try looking at the first three examples in the 'Some Examples' section. If you still don't understand, post a message on the help forum (note: you must be a member of Pure Felinity to access this resource) with your problem and someone should be able to help you understand.
Genetics Help Home
Overview of the different genes used
Explanations of the genes
How to work out the results of a breeding (current page)
Some examples of breeding calculations