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
What is the DNA Tests for Genetic Defects (HYPP) in Horses
• HYPP – Hyperkalemic periodic paralysis
– Disrupts sodium ion channel protein in the membrane of muscle cells.
• The genetic defect disrupts the channel’s normal opening and closing, such that uncontrolled sodium influxes occur.
• These influxes in turn change the voltage current of muscle cells, causing uncontrolled twitching or profound muscle weakness.
• Horses with HYPP can experience unpredictable attacks of paralysis, which in severe cases, can lead to collapse and sudden death.
What is the DNA Tests for Genetic Defects (Scrapie) in Sheep
• Scrapie susceptibility
– Scrapie, along with BSE and CJD, is a member of the TSE (transmissible spongiform encephalopathy) group of diseases.
• Degenerative disease of the sheep’s nervous system.
• Cause is a prion that alters normal host proteins in the
brain and spinal cord– A sheep’s natural resistance to
scrapie can be determined by performing a DNA test.
• Variation at three positions (called codons) within the prion protein (PrP) gene determines the animal’s level of resistance.
What is the use of Hereditary Disease Tests in Dogs
• Hereditary disease testing can allow for accurate
diagnosis of disease status of a dog (clear, carrier or affected).
• Testing for hereditary diseases helps to create a clearer picture for the future health of animals.
• Market pedigree dogs as “disease free”
what is DNA Tests in Dogs for
• Clear By Parentage
• Allows breeders to certify any offspring as clear of a
hereditary disease where the dam and sire have been
DNA tested and cleared of that disease
• To confirm and/or establish pedigree relationships
• To measure the level of genetic variation and inbreeding
• To identify genetically distinct lineages within the population and establish which individual belongs to which lineage
