Population genetics: Companion Animals Flashcards
What are the 4 genetic forces?
- genetic drift (and inbreeding)
- selection
- migration (out-crossing)
- mutation
When does genetic drift occur?
when there is a small population size
When does a bottleneck occur?
usually because of the death of a large number of animals. exacerbates genetic drift
What term describes: ‘related individuals have a chance of sharing common alleles’
Coancestry/kinship
What is the inbreeding coefficient? How do you work this out?
A probability that the 2 copies of a gene are IBD for example (0.25 for offspring of a full sib mating or a parent/offspring mating; 0.125 for offspring of a half sibling mating; 0.0625 for offspring of 1st cousins).
To work out the inbreeding coefficient you need to add the probability of each allele occurring.
List some inherited recessive diseases 4
Primary lens luxation (PLL)
Progressive retinal atrophy (PRA)
Fucosidosis
Leucocyte adhesion deficiency (CLAD)
Which horses are prone to Foal Immunodeficiency Syndrome (FIS)?
Fell and Dales ponies
Clinical signs - foal immunodeficiency syndrome
Weight loss, failure to suckle, increased salivation, dull demeanour, opportunisitic infections (Diarrhoea - Cryptosporidium, Nasal discharge - adenovirus, glossal ulceration/hyperplasia - yeasts), anaemia, b-lymphocyte deficiency
What is inbreeding depression?
Inbreeding that results in very sick individuals and/or compromised fitness of the whole inbred lie/
What is the rate of inbreeding? (delta F)
Delta F = change in average inbreeding coefficient over time (or generations)
What is Ne? What is the formula for it?
= Effective population size.
The rate of inbreeding (delta F) is proportional to the effective population size:
Ne = 1/(2* delta F)
Ne can be thought of as the number of breeding individuals in a hypothetical random mating population that would have the same rate of inbreeding seen in a real population
In which breeds do population sub-structures exist?
More popular breeds such as Labradors
What does diversity loss increase the risk of?
emergence of new inherited disease.
How should inbreeding be controlled?
Control the rate of inbreeding (delta F) to no more than 0.5% per generation where this translates to Ne = 100 *at least). If below this, fitness of the population will steadily decrease and the population will become unviable in the long-term.
List 5 possible solutions to inbreeding
- minimizing coancestry (kinship) of matings
- increasing numbers of animals used for breeding
- equalising the use of males and females
- optimising genetic contributions
- out crossing
What is the Kennel Club Mate Select?
a way of finding a mate for your KC registered dog.
List 3 ways of performing genetic evaluation of individuals
- single locus genotyppes - DNA tests
- EBVs
- Genomic breeding values (GBVs)
What gives an indicator of genetic risk?
The spectrum of alleles that code for the different genes that underly a disease.
How can a complex disease (more than one gene) be assessed?
Phenotypic data (large and representative sample) and pedigree indicates genetic variation, heritability, genetic correlations and EBVs. These are processed using complex statistical techniques called residual estimate maximum likelihood (REML) and best linear unbiased prediction (BLUP).
Define heritability
The proportion of phenotypic variation made up of variation in the genes
Is disease heritability population specific? Examples?
Yes - e.g. hip dysplasia - labrador, GSD elbow dysplasia - GSD osteosarcome - scottish deerhound deafness - border collie syringomyelia
What are EBVs? Use?
The estimated genetic liabilities of disease. They are a good way of increasing the accuracy of your selection
What method is more accurate than EBVs?
DNA because a DNA sample can be taken before maturity and regions of the genome can be assessed for effects in specific ‘problem’ gene (s, areas) before the environment has much/any effect
How are GBVs different to EBVs?
GBVs also include genetic data in the analysis
Why does it matter that EBVs are continuous?
Most DISEASES aren’t continuous so EBVs are continuous which means that we can distinguish between clear dogs with a low and high genetic risk of disease.
What are EBVs good for assessing? Why?
Binary traits
What can help you determine if a trait improvement is selection or environmental?
EBVs
What is selection intensity (i) as a formula?
Selection intensity (i) = mean of selected individuals - population mean
(i.e. the difference between these)
How fast is the response if the selection intensity is small/narrow?
Slow
How fast is the response if the selection intensity is large/wide?
Fast (same response in less time as if a small selection intensity was used however inbreeding needs to be more carefully balanced in this instance).
What are the steps to success with breeding? 4
Population-wide breeding goals
Good data collection procedures
Appropriate genetic evaluation
sufficient selection pressure
