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23 Cards in this Set

  • Front
  • Back
Preventive Medicine

Selective Breeding
a. cull decisions, few genetic diseases are treatable i.e. diabetes
b. breed best to the best i.e. fastest horse, highest milk
Improve growth, performance, etc.
Majority of clients will be purebred breeders and their primary product is genes-selling genetics of the animal
Reputation of clients is based on genetics-confidentiality
Client seek genetic counseling
Non-directive or at least non-dictatorial advice
What does genetic mean?
-not equal to congenital(present at birth)
-is equal to inherited and similar to familial
Genetic Syndromes
Group of anomalies which present together (often chromosomal, can be congenital)
Incidence of Congenital defects
Minor 6% Major 2%
Minor 7% Major ?

~50% are lost before birth
Patterns of Inheritance
single gene
Family History
-age of parents
-number of previous offspring normal and abnormal (large animal producers forget abnormal)
-sex of all affecteds
-number of miscarriages and still births (difficult to determine)
Single gene inheritance
dominant or recessive
dominant or recessive
Autosomal Dominant Generalizations
-Most non-enzyme protein disorders
-variable expressivity (degree)
i.e. Bob tail dogs, manx->can have dribble problems, stumpy is more healthy
-Reduced penetrance (present or not)
-Full all individuals w/ allele express the phenotype
-Reduced not all individuals i.e. 70% penetrance= 70% w/ allele express the phenotype
Malignant Hyperthermia in pigs and dogs
Parrot Mouth in horses
-Many are the result of a new mutation
i.e. Dwarfism is age related but 50% chance of being passed on in a bull, old> 5yrs.
Homozygous Dominant Lethals
-Manx cats and sheep
-Mexican Hairless Dogs
-Roan Horses and sheep
-Overo Horses
White spots don't pass over the back
-Heterozygous for 2 adjacent base pair changes in EDNRB
-Homozygous normal horses have no white spots
-Homozygous white foals die in utero lack enterio ganglia-no innervation to the gut
Halothane- Malignant Hyperthermia (PSS)
Dogs may die on surgical table (can plug into ice decrease metabolism)

Can dominance be excluded?
clinical exam of parents must be thorough since reduced penetrance and variable expressivity are common
Codominant traits
Heterozygote has a different phenotype than earlier homozygote
i.e. Merle in dogs-Australian Sheep dogs
Mostly white MM (problems w/ hearing/seeing), white/black spots Mm, Collie look mm
i.e. chestnut or sorrel CC, palamino Ccr, creamello crcr only guarantee of palamino is mixing to 2 other ones
-both alleles contribute to the phenotype
Autosomal recessive generalizations
-most enzyme deficiencies (inborn errors of metabolism)
-phenotype is consistent
-symptoms often severe
-consanguinity common (related,share blood)
Many diseases are called autosomal recessive b/c neither parent looks affected but better proof recessivexrecessive = 100% recessive offspring

enzyme deficiencies i.e.
pyruvate kinase-abyssinian cat, Westies
phosphofructokinase-springer spaniel

Black Hair Follicular Dysplasia
-black hair comes in grey, blue eyes
-gray hair falls out
-skin beneath becomes wrinkled, pustulent
-melanophilin defect
Implications of Autosomal Recessive
-cull the homozygote affected
-both parents are obligate carriers cull??
-2/3 of siblings are carriers cull??
Carrier Detection
-Breed test=test cross
-to determine if ? carries or recessive:
mate it w/ either known carriers or known affecteds
1. Mate w/Carriers
-spider syndrome in sheep
(dna test available since 1998)
16 offspring all ok=99% chance sire SS
if Ss X ?
1/4 lambs affected
then ?=Ss
2. Does ? carry horned in cattle
-mate ? bull w/ homozygous pp horned cows
-polled in cattle is dominant to horned
7 offspring all ok= 99% (chance to sire)
(1/2)^7=0.0078 therefore <1%

test #offspring prob.detect
dams aa 5 97
1/2^n 6/7 98/99
dams Aa 11 95
1/4^n 16 99
Direct tests
i.e. gene is known
-Biochemical Assay
Niemann-Pick Disease in cats
--enlarged spleen and liver
--CNS damage
Sphingomyelinase is measured
DNA test
-most tests now based on PCR which is a method to amplify small amounts of DNA
i.e. Periodic paralysis in quarter horses
-autosomal dominant
-a.a. change in sodium channel gene

multiple mutations can lead to some disease
alpha-mannosidosis in cattle
angus and galloway 1 point mutation
murray grey-alternative point mutation
cystinuria in dogs
Indirect tests
-used when the causative gene is not yet known
-location of gene, or biochemical pathway, etc is known
-less accurate than direct tests
i.e. depends on distance to gene
Linkage tests
-use a marker (variable piece) linked to causative gene
-gene mapping is a current research focus
-allele that segregates w/ the gene is pedigree specific
-therefore must sample family
-generally DNA variation w/i an intron (non-coding) or other non-coding segments
-microsatellites are repeat of CT or TA or ...
-do not effect any phenotype so have accumulated in animals
-single nucleotide polymorphisms (Snps)
--can be found in coding region
--may or may not affect gene