Genetic Counseling Flashcards

1
Q

Where is the useful genetic variation in a breed?

A
  • In the dogs that founded that breed.

- Therefore, genetic diversity is finite.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What happens with each generation?

A
  • Each generation, alleles can be lost by chance (genetic drift)
  • Also through artificial selection by breeders who select for dogs with the traits they like and remove other dogs from the breeding population
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Can genes that are lost be replaced?

A
  • No, the stud book is closed.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

True/False: From the moment a breed is founded and stud book is closed, loss of genetic diversity over time is inevitable and relentless.

A

True.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

True/False: You can remove a single gene from a population.

A

False.

You cannot; you must remove an entire dog and all the genes it has.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why can’t you select for or against a single gene?

A
  • Genes tend to move in groups with other genes (called linkage)
  • If you select for or against one, you select for or against them all.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

True/False: You can breed for homozygosity of some traits without breeding for homozygosity of other traits?

A

FALSE.

Breeding for homozygosity of some traits breeds homozygosity of all traits.

It is the kiss of death to the immune system.

As genetic variability decreases, so does the ability of the breeder to improve a breed through selection, because selection requires variability.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are consequences of inbreeding?

A
  • Decreased fertility, difficulty whelping, smaller litters, higher puppy mortality, puppies that don’t thrive, shorter lifespan, etc.
  • Genetically healthy dogs should get pregnant if mated and have large litters of robust puppies with low mortality.
  • Animals that cannot produce viable offspring are removed by natural selection.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What happens to mutations of dominant genes if they reduce fitness?

A

-They are removed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

When do recessive mutations have an effect?

A
  • Only if they are homozygous.
  • If an animal is homozygous for a rare mutation, that mutation won’t be removed but will be inherited from one generation to the next
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What happens if you create a bunch of puppies from your favorite sire?

A
  • You are making dozens of copies of all the bad mutations in that dog (which may have never been a problem before because they were recessive
  • This will disperse those bad genes out into the population
  • Previously rare mutation will become common, frequency increases, and chances go up that a puppy will be produced that is homozygous (two copies of the bad allele)
  • Homozygous recessive alleles are no longer silent
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

True/False: genetic disorders caused by recessive alleles “suddenly appear”.

A
  • False

- Defective gene was probably there always, but if you make a zillion copies, you will have a disease

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

True/false: Using DNA test ing to try to remove disease genes from the breed will not make dogs healthier

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What will happen to the genes in a breed every generation?

A
  • They will be lost

- This will happen until the gene pool no longer has the genes necessary to build a healthy dog

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

If a breed looks wonderful now does that mean it’s healthy?

A
  • Not really as a whole.
  • It will suffer from the ill effects of genetic impoverishment with time (inbreeding depression, diseases caused by recessive alleles, increased risk for cancer, etc.)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Can you improve the health of individual dogs without improving the genetic health of the breed?

A
  • No, you must manage the health of the breed’s gene pool
17
Q

Population genetics and breeding

A
  • Population genetics provides tools for the genetic management of breeds or other groups of animals. Breeders CAN improve the health of the dogs they breed if they understand and use them.
18
Q

How did breed diversity happen so quickly?

A
  • Genetic mutation is relatively rare and not the only explanation
  • Single trait selection effect
  • Like with silver fox domestication research; they became more silver along with the genes for domestication I guess
19
Q

Tameness and neuroendocrine function

A
  • Delayed development of adult characteristics
  • HPA function
  • Melanin stimulating hormone receptors in hippocampus and hypothalamus
  • Huge impact on phenotype by selecting the genotype
20
Q

Caveats of pedigree analysis

A
  • While helpful if you have the data, many times animals that have problems don’t have this data
21
Q

Some genetic caveats to recessive and dominant

A
  • Sex linked or associated genes
  • Genes with multiple configurations or alleles
  • Polygenetic characteristic
  • Incomplete or partial dominance
  • Variable expressivity
  • Co-dominant gene
  • Lethal gene (homozygous offspring may not reproduce)
  • Epistasis (one gene affects characteristics displayed by another gene
  • Delayed onset - breeding may occur before disease is seen
  • Modes of inheritance of any particular disease may vary from one breed to another
22
Q

Progeny testing

A
  • Requires large #s of offspring, some of which are affected
  • Progeny must be followed until disease can be expressed
  • Most attention is given to males since they can produce many more offspring than females
  • Breed to unrelated phenotypically similar females
  • Not common for companion animals
23
Q

Test mating unknown to homozygous recessive

A
  • As number of normal offspring increases, your probability of being a carrier drops down significantly
  • Starts at 50%
24
Q

Test mating unknown to heterozygous carrier

A
  • ame deal
  • But if normal offspring is only 1, still a 75% chance of being a carrier
  • doesn’t really drop down until 16
25
Q

What is the rate of genome loss per year in some breeds?

A

Around 1% in some breeds

26
Q

Inbreeding coefficient

A
  • Probability that the two alleles at a locus descend from the same ancestor
27
Q

How much does inbreeding coefficient increase?

A

1% per generation ~

28
Q

Breeding basics

A
  • breeding to reinforce phenotype requires close breeding
  • Other unknown good and bad traits are reinforced at the same time
  • Attention to characteristics and excluding health concerns leads to an increase in genetic disease
  • It is possible to breed for health, structure, and performance
29
Q

What should selection of breeding animals be based on?

A
  • Several factors including goals, health, conformation, performance, and behavior
  • A single minded focus on eliminating one genetic defect will probably result in diminished genetic diversity and increased occurrence of other defects
30
Q

Planning for breeding (we skipped in class)

A
  1. Determine goals of breeding program (health, conformation, temperament, performance)
  2. Determine genetically based health issues in a breed
  3. Outline health clearances and genetic testing
  4. Collect known phenotype and genotype for relatives of the breeding pair
  5. determine if heritability estimates exist for important traits
  6. Identify and evaluate both desired and undesired traits in a breeding pair, parents, and progeny
  7. Check for estimated breeding value calculations
  8. Compare risks of genetic defects with likelihood of superior puppies
  9. Plan for offspring with undesired phenotype and genotype
31
Q

How to maintain genetic diversity with known genetic mutation?

A
  • Test for mutation at a reliable lab
  • Current commercial testing labs vary widely in quality
  • Breed only heterozygous or homozygous normal
  • With direct mutation test, the genetic defect can in the best circumstance be eliminated from line within 6 generations
  • Frozen semen banks are important source of genetic diversity
  • Outcrossing to similar breed then back crossing can be used for extremely limited genetic pools, but it will break the purity of the registry
32
Q

Direct DNA mutation test

A
  • High specificity
  • Same clinical syndrome may be the result of different defects in different breeds
  • Can help you identify true models of human disease
33
Q

Indirect linkage based test (skipped)

A

Proximity of genetic defect to known micro satellites

  • Indirect assessment with inherent error based on the distance between the gene and the micro satellite