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.

Figure 1. Mating combinations possible with an autosomal recessive genetic condition.

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 catalog/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". For a comprehensive list of genetic defects in cattle please visits OMIA's cattle defects page

Table 1. Selected recessive genetic conditions currently being monitored by U.S. breed associations. For a more complete discussion see Online Mendelian Inheritance in Animals (OMIA)

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
Delayed Blindness (DB)	Hereford	Nonlethal	Yes
Developmental Duplication (DD)	Angus	Nonlethal	Yes
Digital Subluxation (DS)	Shorthorn	Nonlethal (influenced by PHA genotype)	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	Yes
Factor XI Deficiency (F11)	Wagyu	Nonlethal	Yes
Freemartin (FM)	All	Sterile female	Yes
Idiopathic Epilepsy (IE)	Hereford	Nonlethal	Yes
Mandibulofacial Dysostosis (MD)	Hereford	Lethal	Yes
Maple Syrup Urine Disease (MSUD)	Hereford	Lethal	Yes
Neuropathic Hydrocephalus (NH)	Angus	Lethal	Yes
Osteopetrosis (OS)	Angus and Red Angus	Lethal	Yes (Red Angus)
Progressive Ataxia (PA)	Charolais	Lethal	Yes
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