How DNA parentage testing works for you

This article was originally printed in the October / November 2000 issue of Tracking The Industry. . .

As the Canadian deer farming industry develops there is an increasing emphasis on high quality genetics. The profitability of any game farm will depend on producing reliable lines of big bucks for sale or for the next generation of breeding stock. This will depend on the ability to keep track of pedigrees on both sides over several generations. Breeding stock development also depends on careful choices when bringing outside genetics into your farm. The DNA test not only shows the correct parentage, but provides independent certification of animal identity and parentage for the buyer and seller.

In this article I will briefly describe how DNA parentage testing works. The test report should be clear and straightforward and the user should have no trouble understanding it. I also want to point out how the breed associations can work together to use the DNA tests as a registration system and ensure value and quality control.

The parentage test starts with three genetic profiles from three animals: the prospective sire, the dam and the calf. The genetic profile (or genotype) consists of several groups of two numbers. Each group is called a "locus" or "marker", which is usually named by an obscure name such as XL123. This is just a name, (which could just as well be "Bob") and it represents a unique part the total genetic makeup of any animal. All test labs use the same names for genetic loci and they have to be the same for test results to be comparable between different labs. For each locus, there are two numbers, usually somewhere between 100 and 300. These numbers represent the two forms of that locus present in each animal and they are called "alleles". Deer, humans and all other animals (and even plants) have two copies of each gene. There are usually lots of different alleles present in a given group of animals, but each individual has a selection of two.

As an example; the buck "Buddy", may have the following genetic profile (or genotype) at locus X21: 121 / 123. A complete genetic profile usually includes a list of several different genes or loci, such as the list of five loci for Buddy in Table 1 below. The fawn and the mother are examples of two other genetic profiles.

How is this used for parentage testing? DNA testing lets you look for both of the parental genes in the offspring. Gregor Mendel discovered over 100 years ago (and it is still known to be true) that each offspring gets one allele from each parent. For example if a fawn were of the following genotype: locus BC1, alleles 177 / 173 ; then the sire and dam could be 175 / 177 and 171 / 173. There are several different combinations that would work, but the test works because there are many more that would not work. The chance of a random error is greatly reduced by looking at several different loci at once. For a positive match, they must all agree.

Table 1: The following is an example set of three genotypes where sire "Buddy" and dam "Janey" qualify to calf "Mikey".

In this case both the sire and dam match the calf. Because of Mendel's law, we know that one allele came from the dam and we can check for the other one in the prospective sire. For example at gene X21, allele 125 must have come from the dam, so the sire must have allele 123 in him. For a match, each of the tested loci must agree, and usually 11 to 15 (or more) different loci are used.

The test can be done with just the sire and calf (or just the dam and calf). In that case the test is done by checking that at least one of the calf's two loci is present in the sire. The sire-calf test is not as reliable because it is much easier for the sire to qualify; you are looking for either one of two alleles. If the other parent is known then there is only one possibility left over. When you receive a report which qualifies a given sire you should check whether the dam's genotype has been used in the test, even if you are only interested in confirming the sire.

The above example lists five different genetic loci. In most animal parentage tests 9 to 15 different loci are used. They all have to agree for the test to indicate a match. The reasoning is that the harder it is to get the match, the stronger the test.

One weakness of the DNA test is that full siblings of the true parents may erroneously qualify as true parents. This is even more difficult in a line-bred herd where the siblings may have very similar genetic profiles. At NBS we have had experiences with elk herds where a given calf will DNA qualify to two or three cows, even when we use 15 different genetic loci and when both parents are tested. This problem should be less common with Mule and White Tail Deer because they tend to have more genetic diversity, which means that there are more different alleles to chose from at each genetic locus.

One useful aspect of the parentage test is that your signed report provides an independent certification of parentage. This will ensure the buyer and seller that the animal brings in the high-quality pedigrees desired for the breeding program. To be sure that your test report meets that need, you should check that the report is from a reputable laboratory and be sure that the report has been signed by the laboratory director. Check that both the sire and dam are tested, even if you are only interested in one of the two parents. Also, check that the report includes proper tracing back to the original samples; for example, was the original blood sample taken by a veterinarian? Ask the laboratory director if the genetic loci could be re-tested by an independent laboratory - in some labs they use their own proprietary set of loci and these may not be available to other laboratories. You would be faced with the need to re-test your entire herd if you wanted to use a different lab.

Another way to make it easier to share test results with other producers is to do some background work with other members of your producers association. A good administrator can set up a registration database using a spreadsheet program such as Microsoft Excel or Microsoft Access, and the data can be transferred by e-mail. The producer's organization can ask test labs to submit descriptions of their quality assurance systems. The producers can also submit split-samples every now and then to ensure that the test results are consistent and reliable. With a given set of loci the results should be the same every time, even between different test labs. In these ways, you can be sure that DNA testing can increase your competitive advantage by helping you produce higher quality deer stocks.

Odd Bres

Northern Bioidentification Service Ltd.

- Back to Library -

Please report any technical problems with this site to the webmaster