Genetic defects Flashcards
What are the types of genetic defects
- Lethal
- Detrimental
- Others
What is lethal genetic defects
– A lethal gene is one that causes death of the individual sometime between conception and old age.
– Frequently lethal genes cause death at birth or shortly
thereafter.
What is detrimental genetic defects
– A detrimental gene is one that is deleterious to the
organism, but does not cause death.
– Reduces vigor and vitality, but does not cause death.
Example – dwarf gene.
What are the other genetic defects
– Genes that do not cause death or affect performance; they just affect the aesthetics (appearance) of the animal.
– Example – hair whorls in swine
• Are like a cowlick
• Are merely aesthetic (do not affect performance), but pigs with hair whorls cannot be registered
What are the genetic defects in cattle
- CVM – Complex Vertebral Malformation
- Deficiency of Uridine Monophosphate Synthase (DUMPS) in Holsteins
- Bovine Leukocyte Adhesion Deficiency
(BLAD) - Pompe’s Disease
- Arthrogryposis Multiplex (AM) (Curly Calf Syndrome)
- Neuropathic hydrocephalus (NH), or “water head”
- Fawn Calf Syndrome
- Parrot Mouth
- Hairless Calf
What is CVM – Complex Vertebral Malformation
– Genetic defect in Holsteins that causes aborted fetuses and stillborn calves
• Affected calves are often stillborn, typically 1-2 wk prior to the expected calving date
• However, many fetuses are aborted earlier in the gestation period
– The most noticeable defects are malformed legs with flexed and rigid pasterns
• A shortened neck may also be noticed
What is Deficiency of Uridine Monophosphate Synthase (DUMPS) in Holsteins
• Recessive genetic defect that causes a failure in the synthesis of DNA
– Characterized by lowered blood activity of the enzyme uridine monophosphate synthase
– Embryos inheriting two copies of the gene are lost around day 40 of pregnancy
– DNA test available
What is Bovine Leukocyte Adhesion Deficiency (BLAD)
– Autosomal recessive congenital disease found in
Holsteins
• Characterized by recurrent bacterial infections, delayed wound healing and stunted growth, and is also associated with persistent marked neutrophilia
• Cattle with BLAD have severe ulcers on oral mucous
membranes, severe periodontitis, loss of teeth, chronic pneumonia and recurrent or chronic diarrhea.
• Affected cattle die at an early age due to the infectious complications
What is the Pompe’s Disease
• Lethal recessive genetic defect
– Calves typically die between 6 and 12 mo of age
– Found in Shorthorn and Brahman breeds
– Calves lack activity of the essential enzyme acidic α-glucosidase
• Excess glycogen builds up inside muscle and nerve cells, interfering with normal tissue function
• Suffer from progressive muscle weakness
What is Arthrogryposis Multiplex (AM) (Curly Calf Syndrome)
- Curly shape of the spine when the calf is born and other symptoms include small size and thin appearance, and rigid legs which may be hyperextended
- Recessive lethal condition found in Angus
- Mutation cause the failure of one of the two genes to produce a critical protein in development of nerve and muscle tissue
- DNA test available
What is Neuropathic hydrocephalus (NH), or “water head”
- The cranial cavity is filled with fluid and no recognizable brain tissue is evident.
- Calves are usually born dead or die shortly after birth
- A lethal recessive defect found in Angus
What is Fawn Calf Syndrome
• Thought to be a simple recessive trait found in Angus
• The clinical signs are similar to congenital contractural
arachnodactyly (‘Arachnodactyly’ refers to the abnormally long bones.)
• Nonlethal some die at or near birth
• Some survive and reproduce
• Muscle contractures of the legs
• Curvature of the spine
• Poor muscling
What is Parrot Mouth
- Cattle have a short lower jaw
* Inherited as a simple recessive trait
What is Hairless Calf
- Found in Herefords
- Nonlethal genetic defect
- Simple recessive
- Occasionally the hairless lesions may occur in multiple sites
How to Eliminate Genetic Defects?
• Commercial herd
– Cull the offspring with the defect, cull the sire of the offspring with the defect, and replace the sire with an unrelated sire.
How to Eliminate Genetic Defects in a Seedstock Herd
– Cull the offspring with the defect
– Cull the sires of the offspring with the defect
– Replace those sires with sires that have a “clean” pedigree
• Avoid buying a carrier sire, because some of the females in the population may be carriers and may produce progeny with the defect if bred to a carrier sire
Dd♂ x Dd♀
¼ DD : 2/4 Dd : ¼ dd
(3/4 normal : ¼ defective)
– Cull all females that have produced defective progeny
(they are carriers)
• Sell females or keep for progeny testing
– Cull other close relatives (such as brothers & sisters)
of affected animals, because they may be carriers
– Females with the defect may be used to progeny test
prospective breeding animals
– Progeny test prospective herd sires
What determines how many of these steps to take in a
seedstock herd
– Economic importance of the defect
– Frequency of the defect in the breed
– Importance other seedstock (elite) or commercial producers put on the defect
Genetic or Environmental Cause of a Defect?
• Indications defect is genetic
• Indications that defect has environmental
cause
It has both
Indications defect is genetic
– Defect occurs only in certain breeding groups
– Defect occurs in herds where inbreeding is practiced
– Defect occurs in more than one season when diets and environments are different
– Defect occurs at a low frequency
– Defect occurs more frequently in one breed
Indications that defect has environmental cause
– Defect occurred when the diet of the dam was deficient or when she was under other stress
– Defect did not occur again after diets or environments improved
– Defective offspring clustered in same year or season
– Defective offspring occur frequently
Progeny Tests for Recessive Genetic Defects
• Most genetic defects are due to a recessive allele at a single locus
• Several types of progeny tests are available to determine the genotype of a potential herd sire if the defect depends on a recessive allele at a single locus
• A normal appearing male
– He may be DD or Dd
– Breed him to a group of test females to determine his genotype
• Important to know if the male is a carrier (Dd) of the allele for the defect
• Particularly important if the male will be used in an AI program
DNA Tests for Genetic Defects
- DNA-based tests for carriers of recessive genes affecting color, polled vs. horned, genetic diseases, and other characteristics of interest are becoming available.
- When the exact location of the gene of interest is known, these DNA tests can detect carriers with 100% certainty.
- If the exact location of the gene of interest is not known, but the location of a closely linked gene is known, the other gene can be used as a marker.
What is Genotyping
- Genotyping is DNA testing
- A simple blood/tissue test is used to determine an animal’s genotype
- A animal’s genotype never changes so only one test should be needed
- Genotype can be determined at any age
What is the DNA Tests for Genetic Defects (PSS) in Pigs
PSS – Porcine Stress Syndrome
– Includes a group of conditions associated with a recessive gene:
- Acute stress
- Muscle tremors
- Rapid respiration
- Sudden death (usually within 15-20 min)
- Rigor mortis within 5 min after death
- Pale, soft, exudative (PSE) meat
