Population genetics: Companion Animals

Question 1

What are the 4 genetic forces?

Answer 1

• genetic drift (and inbreeding)
• selection
• migration (out-crossing)
• mutation

Question 2

When does genetic drift occur?

Answer 2

when there is a small population size

Question 3

When does a bottleneck occur?

Answer 3

usually because of the death of a large number of animals. exacerbates genetic drift

Question 4

What term describes: ‘related individuals have a chance of sharing common alleles’

Answer 4

Coancestry/kinship

Question 5

What is the inbreeding coefficient? How do you work this out?

Answer 5

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.

Question 6

List some inherited recessive diseases 4

Answer 6

Primary lens luxation (PLL)
Progressive retinal atrophy (PRA)
Fucosidosis
Leucocyte adhesion deficiency (CLAD)

Question 7

Which horses are prone to Foal Immunodeficiency Syndrome (FIS)?

Answer 7

Fell and Dales ponies

Question 8

Clinical signs - foal immunodeficiency syndrome

Answer 8

Weight loss, failure to suckle, increased salivation, dull demeanour, opportunisitic infections (Diarrhoea - Cryptosporidium, Nasal discharge - adenovirus, glossal ulceration/hyperplasia - yeasts), anaemia, b-lymphocyte deficiency

Question 9

What is inbreeding depression?

Answer 9

Inbreeding that results in very sick individuals and/or compromised fitness of the whole inbred lie/

Question 10

What is the rate of inbreeding? (delta F)

Answer 10

Delta F = change in average inbreeding coefficient over time (or generations)

Question 11

What is Ne? What is the formula for it?

Answer 11

= 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

Question 12

In which breeds do population sub-structures exist?

Answer 12

More popular breeds such as Labradors

Question 13

What does diversity loss increase the risk of?

Answer 13

emergence of new inherited disease.

Question 14

How should inbreeding be controlled?

Answer 14

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.

Question 15

List 5 possible solutions to inbreeding

Answer 15

• minimizing coancestry (kinship) of matings
• increasing numbers of animals used for breeding
• equalising the use of males and females
• optimising genetic contributions
• out crossing

Question 16

What is the Kennel Club Mate Select?

Answer 16

a way of finding a mate for your KC registered dog.

Question 17

List 3 ways of performing genetic evaluation of individuals

Answer 17

• single locus genotyppes - DNA tests
• EBVs
• Genomic breeding values (GBVs)

Question 18

What gives an indicator of genetic risk?

Answer 18

The spectrum of alleles that code for the different genes that underly a disease.

Question 19

How can a complex disease (more than one gene) be assessed?

Answer 19

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).

Question 20

Define heritability

Answer 20

The proportion of phenotypic variation made up of variation in the genes

Question 21

Is disease heritability population specific? Examples?

Answer 21

Yes - e.g.
hip dysplasia - labrador, GSD
elbow dysplasia - GSD
osteosarcome - scottish deerhound
deafness - border collie
syringomyelia

Question 22

What are EBVs? Use?

Answer 22

The estimated genetic liabilities of disease. They are a good way of increasing the accuracy of your selection

Question 23

What method is more accurate than EBVs?

Answer 23

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

Question 24

How are GBVs different to EBVs?

Answer 24

GBVs also include genetic data in the analysis

Question 25

Why does it matter that EBVs are continuous?

Answer 25

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.

Question 26

What are EBVs good for assessing? Why?

Answer 26

Binary traits

Question 27

What can help you determine if a trait improvement is selection or environmental?

Answer 27

EBVs

Question 28

What is selection intensity (i) as a formula?

Answer 28

Selection intensity (i) = mean of selected individuals - population mean

(i.e. the difference between these)

Question 29

How fast is the response if the selection intensity is small/narrow?

Answer 29

Slow

Question 30

How fast is the response if the selection intensity is large/wide?

Answer 30

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).

Question 31

What are the steps to success with breeding? 4

Answer 31

Population-wide breeding goals
Good data collection procedures
Appropriate genetic evaluation
sufficient selection pressure