Recessive Genetic Defects

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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.

Figure 4. Mating combinations possible with an autosomal recessive genetic condition. Genetic Condition Mating.jpg

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 that has the potential to create affected offspring under natural selection. 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

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
Beta (ß)-Mannosidosis Salers 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
Dwawrfism (D2) Angus Nonlethal 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 No
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)
Protoporphyria Limousin Nonlethal Yes
Pulmonary Hypoplasia and Anasarca (PHA) Dexter, Maine-Anjou and Shorthorn Lethal Yes
Tibial Hemimelia (TH) Shorthorn and Maine-Anjou Lethal Yes