Genetics 101
A gene contains two alleles, in this case it can contain A1 as one allele and A1 as another allele. Similarly, the other combinations would be one allele A1 and the other A2 or one allele A2 and the other A2. Obviously, we are looking for cows that have two A2 alleles as they are the ones that produce A2 milk with nonbcm7 reactions.
We want to make it clear, there are cows that already exist which have two A2 alleles. The other side of the equation would be what genetic makeup the sire (or bull) is which the cows are bred with and whether offspring will also have two A2 alleles as their genetic makeup. By breeding for and selecting only those cows that have two A2 allele makeup we can ensure milk is produced which will only be nonbcm7. Confirmation can be done through simple genetic testing.
Now, a very basic genetics lesson and examples. In order to calculate the probabilities of what will be produced in breeding, genetic make up must first be determined via genetic testing. Then, by taking the bull and cow alleles into account you can determine the chances of producing off spring with specific genetic makeup. Consider the example of a bull which has an A1 and an A2 allele breeding with a cow that also has an A1 and an A2 allele. Each parent contributes one allele to the offspring so there are possibilities of: A1/A1, A1/A2, A2/A1, and A2/A2. Reminder: Only cows with A2/A2 produce milk that is nonbcm7.
To expand this out to show all possibilities for all combinations, please see the chart below which utilizes Punnett Square methodology. This shows that it is likely approximately 25% of the cows which already exist would be A2/A2. Please keep in mind that this is meant to provide a very easy to understand model and percentages may vary slightly if more complex genetics calculations such as the Hardy-Weinberg equation were used.
As illustrated, the cows needed to produce A2 milk exist today and through thoughtful breeding practices the number of these cows available could be greatly increased.
