DNA (Genetic) Testing – Genotyping
The following is an attempt to simplify a very interesting and important, but complex science. Terminology has been reduced significantly for the sake of simplicity. For a more in depth explanation about this topic please go to https://www.vgl.ucdavis.edu/services/dnatyping.php
What is DNA?
We all know that elephants only give birth to little elephants, giraffes to giraffes, dogs to dogs and so on for every type of living creature. But why is this so?
The answer lies in a molecule called deoxyribonucleic acid (DNA), which contains the biological instructions that make each species, and individual animal unique. DNA, along with the instructions it contains, is passed from adult organisms to their offspring during reproduction, and determines everything about that offspring from nose to tail, inside and out, including invisible traits like behavior, metabolics, fertility, ect., ect., ect.
With just a few tail hairs pulled from the switch of our cows tail, genetic testing laboratories can take the DNA that is found in the hair follicle (not the hair itself) and tell us many things about our animals that might otherwise be unknown.
Genetic testing can
- Determine if our animal carries PHA or Chondro, two deadly genes in the Dexter breed
- Tell us which of the 3 coat colors, black, red or dun, our animal might produce in its offspring, or in the case of red or dun, clarify what color an animal actually is.
- Tell us if the polled gene is present
- Determine beta casein type in milk also known as A2
- Provide genotyping, which can be used as identification for an individual animal.
- Can confirm paternity or maternity
What is Genotyping?
Genotyping is the unique DNA sequence (signature) of an individual animal. Its purpose is to aid in the determination of identification or parentage. That’s it. Genotyping does not identify and report inherent traits that might be hiding in the DNA of an animal. Example: a black animal can carry a red or dun gene in addition to black. A genetic test, not genotyping, could validate that.
A Genetic Marker Report is synonymous with genotyping.
By comparing the Genetic Marker Report of a sire and/or dam to an offsprings, paternity and/or maternity can be somewhat determined (aka “Parentage Verified” or “certified”.) Why only “somewhat”? DNA can only prove that a sire or dam is a parent candidate, or is not a parent candidate, not actually prove that a sire or dam is 100% the parent, but it comes very close – close enough.
When is testing required?
Uncertain Paternity or Maternity
When unsure of who the sire of a calf is, or maybe even the dam, if time has lapsed, then a “Parentage Verification” report can ensure accuracy. A “Genetic Marker Report” from the sire and/or dam, is compared to the offsprings.
If your animal is red, genetic testing for RED is required by the PDCA unless it comes from a red sire or a red dam.
If you are not sure if an animal is red or dun – test for red. If no red is present it is by default dun.
If a horned sire and a horned dam produce a polled offspring – It is the policy of the PDCA to disqualify the animal for registration. Parentage testing is recommended to resolve the discrepancy.
PDCA must have a copy of the animal’s genotype (including the 9 internationally recognized markers) on file, before calves resulting from artificial insemination will be registered
When is testing unnecessary?
PDCA does not require any genetic testing except for the above instances. Although there is value in knowing just what traits might be hidden (or not) in your animals DNA, there are some situations where testing is just unnecessary.
A Genetic Marker Report is not necessary except to verify parentage, or for identification. Specific DNA tests do not require genotyping or a Genetic Marker Report.
PHA and Chondro
If a sire and dam have been DNA tested and are proven to be “non-carriers” of PHA or Chondro genes; their offspring will not inherit the gene either. No need to test their offspring.
If both a sire and dam have been tested and both are proven to carry two sets of A/2 Beta Casein genes (aka A2/A2 or A/2 homozygous) – No need to test their offspring.
For breeders who see added value in genetic testing their stock, PDCA has long offered a registration option called “Certified Registration”. To be “Certified”, proof of genotyping and genetic testing for PHA and Chondro must be provided with the Registration Application. (PDCA does not make judgement between “carriers” or “non-carriers” of PHA or Chondro.)