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Modes of Inheritance; Inherited Animal Genetic Diseases (definitions…
Modes of Inheritance; Inherited Animal Genetic Diseases
inherited genetic diseases
congenital
inherited cause
environmental cause in utero
inherited disorders that are not congenital
late onset
i.e. epilepsy onset at 1-3 years of age
t
o be congenital, must be born with it.
up to 10% of small animals have inherited Mendelian defect
up to 40% of SA have an inherited defect
definitions
locus
gene
allele
genotype
homozygote
heterozygote
phenotype
inheritance
breeds
stock of animals with distinctive phenotype
limited genetics
deliberate selection
breed registry
aka herdbook,
studbook
, register
closed - no outside blood
most dog breeds
some horse breeds
official list
of specific breed animals
Mendelian traits
"simple traits"
controlled by nature of the alleles present at one single locus
single locus allele segregation
homozygous
heterozygous
no environmental influence
patterns
autosomal dominant
doesn't skip generations
= #s Ms and Fs effected
ex.
polycystic kidney disease in cats
2/3 loss in both kidneys beofre dysfunction
most common inherited disease in cats
candidate gene approach
targeted sequencing of PKD1 gene
unique RFLP site mutation causing a stop codon
restriction enzymes
restriction fragment length polymorphisms (RFLP)
PCR
reduced amount of needed protein
in utero lethal for AA
50% offspring affect with clear mating
autosomal recessive
may skip generations
all offspring have 2 affected parents
equal #s of Ms and Fs affected
examples
poodle encephalopathy
bovine citrullinaemia
head pressing
seizures
symptoms very soon after birth
high citrulline concentrations in blood
don't produce citrulline breakdown enzymes
depressed
25% affected from two carriers
x-linked recessive
may skip generations
M to M trasnmission doesn't occur
lower incidence in F
examples
hemophilia
muscular dystrophy
50% M offspring affected
50% F carriers
human history of animal genetics
traits can be passed
trait = genotype + environment
traits can be present but not visible
parents can be "carriers"
planned breeding schemes
propagate deleterious conditions
propogate desirable traits
basic questions to veterinarians
"does it run in families?"
distinguishment between genetics and the environment?
clusters of disease within related individuals
poodle encephalopathy
seizures
congenital
recessive
common sire effect
overuse of popular sires
can simply be used more
females limited by birth amounts
in-vitro increases risk
clustering of recessive traits
is it more common within a single or related breeds?
usually no answer
complex (polygenic) trait
aka multifactoiral
aka quantitative traits
influenced by
number of genes
infleunced by environmental factors
time of day
nutritional state
infectious agent
examples
hip dysplasia
0.1-0.68 heritability
32-89% environmental influences
weight gain/loss
diet
Ca, P
OFA categories
okay to breed
3 - fair, minor degree of subluxation of femoral head
1 - excellent, deep seated femoral head
do not breed
5,6
7 - severe HD, significant subluxation and large amt of secondary arthritic bone changes
checked at 6mo and 2y
controlled by a # of genes which individually exert slight effect on phenotype
heritability calculations
1.0 no environmental effect
0.8 one gene with major effect, 20% environmental influence
0 no genetic influence
Inbreeding
inbreeding coefficients
work towards overall lowering the IC in a breed
possible to have healthy lines
% genes which both copies are identical
mates chosen based on
degree of relatedness
systemic choice
subdivision of population
close stud books
narrow choices
increases homozygosity
affects
all loci
loss of genetic variation
increased expression of hidden recessive alleles
reduce fitness i.e.
inbreeding depression
each human carries 4 lethal recessive alleles on average