Genetics Or Animal Breeding 1

Front 1

Preventive Medicine

Selective Breeding

Back 1

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.

Front 2

Remember

Back 2

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

Front 3

Client seek genetic counseling

Back 3

Non-directive or at least non-dictatorial advice

Front 4

What does genetic mean?

Back 4

-not equal to congenital(present at birth)
-is equal to inherited and similar to familial

Front 5

Genetic Syndromes

Back 5

Group of anomalies which present together (often chromosomal, can be congenital)

Front 6

Incidence of Congenital defects

Back 6

Humans
Minor 6% Major 2%
Cattle
Minor 7% Major ?

~50% are lost before birth

Front 7

Patterns of Inheritance

Back 7

single gene
chromosomal
multifactorial
teratogenic

Front 8

Family History

Back 8

-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)
-breeds

Front 9

Single gene inheritance

Back 9

autosomal
dominant or recessive
sex-linked
dominant or recessive

Front 10

Autosomal Dominant Generalizations

Back 10

-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.

Front 11

Homozygous Dominant Lethals

Back 11

-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

Front 12

Anaesthetics

Back 12

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

Front 13

Codominant traits

Back 13

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

Front 14

Autosomal recessive generalizations

Back 14

-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.
alpha-mannosidase-persian
pyruvate kinase-abyssinian cat, Westies
phosphofructokinase-springer spaniel
cystinuria-newfie

Black Hair Follicular Dysplasia
-black hair comes in grey, blue eyes
-gray hair falls out
-skin beneath becomes wrinkled, pustulent
-melanophilin defect

Front 15

Implications of Autosomal Recessive

Back 15

-cull the homozygote affected
-both parents are obligate carriers cull??
-2/3 of siblings are carriers cull??

Front 16

Carrier Detection

Back 16

-Breed test=test cross
-to determine if ? carries or recessive:
mate it w/ either known carriers or known affecteds

Front 17

1. Mate w/Carriers

Back 17

-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
(1/4)^16=<1%

Front 18

2. Does ? carry horned in cattle

Back 18

-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

Front 19

Direct tests

Back 19

i.e. gene is known
-Biochemical Assay
Niemann-Pick Disease in cats
--enlarged spleen and liver
--CNS damage
Sphingomyelinase is measured

Front 20

DNA test

Back 20

-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

Front 21

Indirect tests

Back 21

-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

Front 22

Linkage tests

Back 22

-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
ONLY A MARKER NOT THE MUTATION
-therefore must sample family

Front 23

Markers

Back 23

-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