by Gabriella Nanci
Markers: The genetic markers used for parentage testing are based on a designated set of microsatellites found in the cattle’s DNA. Microsattelites are the same thing as VNTR’s (Variable Number of Tandem Repeats). They are repeated segments of DNA that are apparently “junk,” i.e. do not actually code for a trait. At a given marker, an animal will be assigned a set of two numbers, which is the number of times the sequence is repeated in that animal on each chromosome, for example 121/134. The number of repeats can be compared to the number of repeats in the animal’s offspring at each marker, to confirm paternity or maternity. If large number of tests were performed on Dexter’s, a database could be formed that would give the parameters of the variation within the entire breed. This would theoretically allow a single questionable animal to be tested and compared to the Dexter population, thus determining likelihood that the animal is in fact a Dexter. This is not available at this time, and in this country, most of the animals being tested are from a limited group of breeders, meaning the database is not representative of the entire breed. Markers can also be used to track certain genes when the exact location of the gene is not known, but its neighboring markers have been identified. This requires several generations of testing on both affected and non-affected animals within the pedigree.
