Understanding GeneProb results2011
The GeneProb analysis interrogates the pedigree of each animal and calculates the probability that the animal is a carrier for each genetic condition from the known DNA information of their ancestors. For example, if an animal’s dam had been tested free of the genetic condition but the sire was a known carrier, the animal would be reported as having a 50% chance of being a carrier.
The gene probability analysis includes all known DNA information for animals recorded on the Murray Grey Beef Cattle Society database, plus DNA information recorded with several other Breed Societies, including Angus Australia and the Red Angus Society. Genetic test results are based on samples provided by breeders.
Disclaimer: The Murray Grey Beef Cattle Society of Australia makes no statements, representations or warranties about the accuracy or completeness of any information relating to the status of a particular animal: and disclaims all responsibility for information and all liability (including without limitation, liability in negligence) for all expenses, losses, damages, and costs you may incur as a result of information being inaccurate or incomplete in any way for any reason.
(First two characters vary with the genetic condition – ie. AM, NH,CA or MA)
_ _ F indicates that the sample submitted for this animal has been tested and found to be free of the causative mutation responsible for the indicated genetic condition. This animal is homozygous free, meaning that it has two copies of the normal variant (or allele) of the gene.
_ _ C indicates that the sample submitted for this animal has been tested and found to be a carrier of the causative mutation responsible for the indicated genetic condition. This animal is heterozygous for the mutation, meaning that it has one mutant allele and one normal allele. This animal could pass the mutation to approximately half of its progeny.
_ _ _ % indicates that, based on pedigree information supplied by the breeder of the animal, the animal has a chance to be a carrier of the mutation responsible for the indicated genetic condition but has not been tested. The higher the indicated percentage, the larger the chance the animal may be a carrier. Breeders are recommended to test this animal for the genetic condition prior to using this animal in a breeding program.
_ _ FU indicates that, based on pedigree information supplied by the breeder of the animal, the animal is expected to be free of the mutation responsible for the indicated genetic condition but has not been tested. However, this animal has not been tested for the causative mutation and the Murray Grey Beef Cattle Society gives no guarantee as to the animal’s “free” status.
_ _ A indicates that the sample submitted for this animal has been tested and found to be affected by the genetic condition. This animal is homozygous for the mutation responsible for the genetic condition and has two copies of the mutant variant of the gene.
It is important to note that the GeneProb results are only current at the date of publishing and are limited by the DNA test result and pedigree information available. The results may change as further DNA testing is performed, particularly when the level of testing that has been conducted is relatively low. The MGBCS Animal Search facility will consequently become the best source of data on an animal’s status, with the GeneProb results being routinely updated in the future.
Putting Undesirable Genetic Recessive Conditions in Perspective
All breeds of cattle, in fact all mammals including humans, have undesirable genetic conditions. Fortunately, advances in molecular genetics have facilitated the development of DNA tests for their management. Breed Societies are at the forefront of development of strategies to manage undesirable genetic conditions and seedstock members are leading the industry with their uptake of this technology.
How are the conditions inherited?
Research in the U.S. and Australia indicates that AM, NH and CA are simply inherited recessive conditions. This means that a single pair of genes controls each condition. For this mode of inheritance two copies of the undesirable gene need to be present before the condition is seen; in which case you may get a calf with AM, NH or CA.
Animals with only one copy of the undesirable gene (and one copy of the normal form of the gene), that appear normal, are known as “carriers”.
What happens when carriers are mated to other animals?
A carrier will, on average, pass the undesirable gene form to a random half (50 %) of their progeny.
When a carrier bull and carrier cow are mated:
- There is a 25% chance that the progeny produced will have two normal genes and so will never pass on the undesirable gene.
- There is a 50% chance that the mating will produce a carrier.
- There is a 25% chance that the progeny will inherit two copies of the undesirable gene and hence be affected by the genetic condition.
When a carrier animal is mated to an animal tested free of the genetic condition:
- All progeny will appear normal and will be unaffected by the condition.
- There is a 50% chance that the mating will produce a carrier.
- There is a 50% chance that the progeny produced will have two normal genes and so will never pass on the undesirable gene.
Note that an animal that is tested free by DNA test of the genetic condition will not pass the genetic condition to its descendants, even if it has carriers in its own ancestry. Therefore, DNA-tested free animals can be used in your breeding program with confidence that they are not transmitting the unfavourable gene to subsequent generations.
How should genetic conditions be managed?
An interesting presentation on the management of genetic conditions was recently delivered as part of the “Know Your Genes” webinar course conducted by Southern Beef Technology Services (SBTS).
Further details regarding each genetic condition are provided below.
Arthrogryposis Multiplex (AM) – Calves affected by AM (also known as curly calf syndrome) are born dead or die shortly after birth. The spine and legs appear crooked or twisted and the joints of the legs are often fixed in position. Front legs are contracted and rear limbs may be contracted or extended. Calves are small and appear thin due to limited muscle development. There may be a cleft affecting the nose or palate. Additional unique features are recognized during laboratory examination.
Neuropathic Hydrocephalus (NH) – Calves affected by NH are born near full term and may have 10 – 15 kg birth weights. Some evidence also points towards early abortions due to the condition. The cranium is markedly enlarged (volleyball to basketball sized). The bones of the skull are malformed and appear as loosely organized bony plates that fall apart when the cavity if opened. The cranial cavity is filled with fluid and no recognizable brain tissue is evident. The spinal canal is also dilated and no observable spinal tissue is found.
Contractural Arachnodactyly (CA) – Calves affected by CA (also known as “fawn calf”) are normally born alive, with normal birth weight and most can walk, suckle and survive. The expression of CA is subtle and hence CA may not initially be recognized as a genetic defect. Contractures which reduce the range of angular movement of the upper limb joints are present at birth but are much less severe, without rigid joint contractures. CA calves assume an abnormal crouched position, resembling an elk or deer fawn, with the feet placed more to the rear than normal, hocks pulled up and back and the spine slightly arched. In their first days of life, CA calves are also flat down on their pasterns. Although there is a reduced range of movement (ie. contracture) in the upper limb joints, particularly the hip, stifle and hock, there is an increased extensibility in the lower limb joints, particularly the pasterns. CA affected calves are reported as taller and more slender, than their unaffected siblings. Affected calves can show significant recovery and usually appear relatively normal by 4 to 6 months of age. As yearlings, the CA calves appear lighter framed and lighter muscled, particularly in the hind quarters. Most perform poorly and remain, tall, slender animals with poor foot conformation.
Mannosidosis (MA) – Affected Angus and Murray Grey calves either fail to survive the immediate postnatal period, or if they do, they show severe, progressive neurological disease characterised by tremors of the head, ataxia, and aggression. The phenotype in Galloways is more severe, with most affected cases aborted or stillborn.