Courtesy of Dr Jenny Cahill
The use of DNA technology is something most of us are familiar with - due to its uses in human forensics. But it also has applications in the equine world, including DNA profiling for parentage, colour and some inherited diseases.
It has been standard in New Zealand for some years that all thoroughbred and standardbred foals undergo DNA parentage verification before registration, and is becoming a common prerequisite to register a foal with other breed societies.
Here are some basic genetic concepts to help you understand the following information on DNA genotyping:
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Chromosomes - long double-stranded molecules of DNA, present in the nucleus of every cell in the body, containing all of the information of inheritance. Chromosomes come in pairs - one from each parent.
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DNA - molecules made up of millions of the four basic repeating units A (adenine), T (thymine), G (guanine) and C (cytosine). Only 10% of DNA sequence actually codes for genes.
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Genes - specific sites on the DNA, containing the information for inherited traits, coded by the specific order of the four bases. Genes and gene markers also come in pairs - known as loci.
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Microsatellites - DNA markers which are present in the 90% of noncoding DNA.
- Allele - form of a gene at its specific locus. There are two alleles at each locus - one from each parent.
DNA is extracted from the hair follicles from plucked mane or tail hair and parentage is verified by comparing specific microsatellites markers in the foal's DNA (the DNA fingerprint) to those of the parents. This uses the principle that one of each pair of microsatellite markers for the foal has come from the dam and one from the sire.
Sometimes the results are unexpected - there will always be surprises when dealing with horses. The expected sire or dam does not match on DNA - mares will swap foals in the paddock, and stallions will use many devious and sometimes seemingly impossible means to reach a mare.
A scientifically-based method for verifying parentage is crucial to any breeding programme, to ensure that pedigree information is absolutely accurate. Reliance on observation, manual identification and record-keeping produces a surprisingly high level of errors. Even in the ‘gold standard' of pedigrees, the Thoroughbred Stud Book, genetic studies showed that up to 50% of maternal/dam lines contained DNA they could not possess if the pedigrees were accurate.
If you would like more information on parentage verification or colour testing in New Zealand, please contact
Dr Jenny Cahill BVSc PhD
Director
Equine Parentage and Animal Genetic Services Centre
Massey University
Palmerston North
J.I.Cahill@massey.ac.nz
