Parentage Verification using DNA

Parentage Verification

Because an animal’s genome is passed down from its parents, genetic analysis forms an extremely useful tool for determining that animal’s parentage. CombiBreed provides several different services for both establishing an animal’s genetic profile, and for comparing it to that of (possible) parents. This information can be used to verify pedigrees and is often a required part of the establishment of an animal’s position in an official breed registry.

Parentage analysis is done by measuring and comparing a number of so-called genetic markers. These markers are distinct pieces of genetic code which are passed down consistently over generations, but which can vary considerably between different individuals. An individual has two alleles of each marker: one from its mother and one from its father. (The exception lies with X-linked markers; see Different Inheritance Patterns). These two copies can be the same allele of a marker, or two different alleles. In the case of a correct parentage (the suspected parents are the offspring’s actual parents), half of the offspring’s marker alleles can be traced back to its father, and half to its mother.

The above table provides an example of correct parentage. In this table, the DNA is shown of three individuals: an offspring (left column), a potential mother (middle column), and a potential father (right columns). Each row gives the two alleles of a given marker in each individual. In this case all variants in the offspring are present in the parents; half in the mother, and half in the father. Therefore, the offspring can indeed be descended from these two parents.

This second table provides an example of incorrect parentage. As with the previous example, it compares the marker alleles of an offspring and its suspected parents. In this case, however, the offspring has several alleles which the father does not (highlighted in italics). Therefore, we must conclude that the suspected father cannot be the offspring’s actual father.

It is important to note that marker-based parentage analysis cannot determine correct parentage with 100% certainty; the only 100% certainty comes with a result of incorrect parentage. However, the more markers are tested, the higher the certainty of a correct parentage. Standardized panels for forming a genetic profile in certain animals therefore test for a wide array of markers.

STR (ISAG2006) vs. SNP (ISAG2020) parentage verification

CombiBreed provides two different forms of marker analysis for establishing a genetic profile: STR and SNP. STRs, or Short Tandem Repeats, are also known as microsatellites or ISAG2006. They consist of a certain fragment of genetic code, usually between one to six nucleotides (letters) long, which is repeated over and over. An STR in a given species is always located in the same position on the genome. The exact number of repeats, however, can vary considerably between individuals. This makes the length of these STRs a useful marker for genetic profiling. A typical STR profile consists of 20 to 40 different markers.

SNPs, or Single Nucleotide Polymorphisms, are the second main marker type. As the name implies, a SNP is one single nucleotide at a given position that can vary from allele to allele. A ‘G’ at the marker location on one allele may be a ‘T’, ‘A’ or ‘C’ on another allele. Because SNPs are far less complex than STRs, more are needed in order to form a reliable genetic profile. A typical SNP profile (ISAG2020) can consist of 200 to 400 different genetic markers.

It is important to remember that the SNP and STR markers used for genetic profiling do not have any effect on an animal’s characteristics, being largely confined to non-coding areas of DNA. Therefore, these panels cannot provide information on an animal’s genetic traits – only its ancestry.