Recessive Genetic Defects
Many genetic defects are recessive, and the reason for this is that mutant alleles often render the resulting protein nonfunctional. In many cases if an individual inherits a functioning allele of a gene from one parent, there is no phenotype associated with inheriting the nonfunctional mutant allele from the other parent. As such a heterozygous “Aa” animal, or carrier, appears normal. It is only when two carriers mate that they have the possibility of producing offspring that have by chance inherited both of the non-functional alleles from their parents. The example gene combinations that can occur with an autosomal recessive genetic condition are shown in Figure 4. Note that if this is a lethal genetic condition, then all of the animals that are represented as solid black would not be alive and so the only possible matings would be between unaffected (green) and carrier (green and red) individuals.
All animals are carriers of mutations somewhere in their DNA for one or many recessive traits. Because an animal must inherit two copies of a given recessive mutation to be affected, and with only a few animals typically sharing the same mutation in the whole population, there is rarely a mating cross between unrelated animals that has the potential to create affected offspring. It is when relatives are mated that there is an increased possibility that offspring will inherit the mutant allele on both sides of the family tree. The Online Mendelian Inheritance in Animals (OMIA) is a catalogue/compendium of inherited disorders, other (single-locus) traits, and genes in 244 animal including an extended list of breed-defining characteristics, such as coat color, polledness, double muscling and twinning. There are currently 523 total traits and disorders listed for cattle at this website. Table 1 lists the genetic conditions that are currently being monitored by U.S. breed associations.
For a more information on genetic conditions please visit: ("Managing Genetic Defects")
Table I. Recessive genetic conditions currently being monitored by U.S. breed associations.
|Genetic Abnormality||Primary Breed(s) of Incidence||Lethal or Nonlethal||DNA Test Available|
|Alpha (α)-Mannosidosis (MA)||Red Angus||Lethal||Yes|
|Arthrogryposis Multiplex (AM)||Angus||Lethal||Yes|
|Bovine Blood Coagulation Factor XIII Deficiency (F13)||Wagyu||Nonlethal||Yes|
|Chediak-Higashi Syndrome (CHS)||Wagyu||Nonlethal||Yes|
|Claudin 16 Deficiency (CL16)||Wagyu||Nonlethal||Yes|
|Contractural Arachnodactyly (CA)||Angus||Nonlethal||Yes|
|Developmental Duplication (DD)||Angus||Nonlethal||Yes|
|Digital Subluxation (DS)||Shorthorn||Nonlethal (influenced by PHA genotype)||Yes|
|Bulldog Dwarfism (BD)/ (Chondrodysplasia)||Dexter||Lethal||Yes|
|Erythrocyte Membrane Protein Band III Deficiency (Spherocytosis) (Band 3)||Wagyu||Often lethal||Yes|
|Hypotrichosis (hairless calf)||Hereford||Nonlethal||Yes|
|Factor XI Deficiency (F11)||Wagyu||Nonlethal||Yes|
|Freemartin (FM)||All||Sterile female||Yes|
|Idiopathic Epilepsy (IE)||Hereford||Nonlethal||Yes|
|Neuropathic Hydrocephalus (NH)||Angus||Lethal||Yes|
|Osteopetrosis (OS)||Angus and Red Angus||Lethal||Yes (Red Angus)|
|Pulmonary Hypoplasia and Anasarca (PHA)||Dexter, Maine-Anjou and Shorthorn||Lethal||Yes|
|Tibial Hemimelia (TH)||Shorthorn and Maine-Anjou||Lethal||Yes|