Population Genetics In Companion Animals Flashcards
How many chromosomes do dogs have?
78
How many chromosomes do cats have?
38
How many chromosomes do rabbits have?
44
How does the number of genes relate to the number of chromosomes as chromosome number varies between species?
Roughly the same number of genes
What does the founder effect mean?
New colony started by a few members of original population
Not all genes from original population present for repopulation:
- reduced genetic variation
- non-random sample of genes from original population
What is a genetic bottleneck?
Occur when a populations size is reduced for at least one generation
Reduced genetic diversity
What are the types of simple/Mendelian inheritance?
Autosomal dominant
Autosomal recessive
X-linked dominant
X-linked recessive
What are the broad categories of inheritance?
Simple
Complex
Selection:natural or artificial
What is the difference between simple and complex inheritance?
Genes interact with each other
Can interact in different ways in each individual to create huge variations in phenotype
What is the definition of reproductive success?
Survival of the form that will leave the most copies of itself in successive generations
What are the ‘genetic forces’ acting on breeds/populations?
Selection (natural or artificial)
Loss of genetic diversity (inbreeding or genetic drift)
Immigration
Mutation
When does genetic drift occur?
In a SMALL population
What is genetic drift
Variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce
What can occur secondary to planned selection?
Give an example
Unplanned selection
Deafness with the extreme piebald gene in Dalmatians, english setters, collies, Aussies, white boxers and white bull terriers
When is molecular genotyping in dogs useful?
Simple inherited disorders - conditions caused by a mutation in just one gene
How are samples obtained for DNA testing in dogs?
Blood or mouth swabs
What is the goal of molecular genotyping in dogs?
Identify clear, carrier and affected dogs
Effectively reduce or eliminate undesirable disease genes
What animals should you breed together (based on clinical presentation and genotype)?
Clinically normal animals
for autosomal recessive, breed clear and carriers etc,
Why shouldn’t you just breed clear to clear?
Reduces genetic variation as cuts out half the population
— will result in more diseases
What animals could you breed with an affected dog?
Why?
Clear dogs
Will get all carriers as offspring
Give examples of some simple genetic conditions.
PRA - progressive retinal atrophy
PLL - primary lens luxation
CLAD
copper toxicosis
Give examples of diseases caused by complex genetics
Hip dysplasia
Elbow dysplasia
Epilepsy
Bloat
Which are more common, simple or complex genetic conditions?
COMPLEX
What can cause differences between genotype and phenotype?
in utero environment Neo natal environment Feed intake Diet Exercise
What is meant by the term heritability?
The proportion of the phenotypic variation made up of variation in the genes
What does a higher heritability indicate?
We can drive away from the condition by breeding
What is the EBV?
Estimated breeding value
Tendency of an animal to pass on or develop a disease
Used for complex disease
What is the difference between the true and estimated breeding value?
True - relevant genotype
Estimated - relevant phenotype
What can EBVs be used for?
Select towards a positive trait
- milk yield in cows
Select away from a negative trait
- hip dysplasia in dogs
When might an individual with bad hips still be used for breeding?
If previous generations have good hips, the implication is that good genes are still present
What is the difference between binary disease traits and EBVs?
Why might this be beneficial
EBVs are continuous
Allow discrimination between ‘healthier’ animals
What is the selection intensity?
The difference between the mean of selected individuals and the population mean
What does an increased selection intensity risk?
Decreased genetic diversity
inadvertently be selecting for other diseases
INCREASED RISK OF INBREEDING
Why does selection increase risk of inbreeding?
Relatives resemble eachother
Selection will result in mating more closely related individuals
What is IBD?
Identical by descent
Have exact same copy of a gene - same alleles
REDUCED HETEROZYGOCITY
What is the COI?
Coefficient of Inbreeding
Probability that two copies of a gene at a locus are IBD
0.5 x relationship between parents
How can inbreeding lead to specific inherited disease?
Reduced number of heterozygotes which ‘hide’ harmful recessive genes
What is inbreeding depression?
Reduction in beneficial traits as a result of inbreeding
What loci does inbreeding depression affect most?
Any locus where heterozygous performance is better than homozygote performance
What is hybrid vigour?
Superior average performance of crossbred progeny compared with the average of their purebreds parent species
How long does heterosis / hybrid vigour last for?
Deteriorates after first generation
What is the effective population size?
The number of breeding individuals in a random mating population that would have the same rate of inbreeding as seen in the real population
How can the effective population size be calculated?
1/ (2x the rate of inbreeding)
What is the ideal rate of inbreeding?
Less than 0.05%
What happens if the effective population size is less than 50?
Population fitness steadily declines and becomes UNVIABLE in the long term
How can you control the rate of inbreeding?
Minimise kinship (coancestry) of matings
Increase number of animals used for breeding
Equalise use of males and females
Monitor genetic contributions
Outcrossing
What is outcrossing?
Breeding animals in the same breed but with completely separate families
What is the ideal effective population size to conserve genetic diversity?
> 500
