Genetic Counseling Flashcards
(33 cards)
Where is the useful genetic variation in a breed?
- In the dogs that founded that breed.
- Therefore, genetic diversity is finite.
What happens with each generation?
- 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
Can genes that are lost be replaced?
- No, the stud book is closed.
True/False: From the moment a breed is founded and stud book is closed, loss of genetic diversity over time is inevitable and relentless.
True.
True/False: You can remove a single gene from a population.
False.
You cannot; you must remove an entire dog and all the genes it has.
Why can’t you select for or against a single gene?
- 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.
True/False: You can breed for homozygosity of some traits without breeding for homozygosity of other traits?
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.
What are consequences of inbreeding?
- 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.
What happens to mutations of dominant genes if they reduce fitness?
-They are removed
When do recessive mutations have an effect?
- 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
What happens if you create a bunch of puppies from your favorite sire?
- 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
True/False: genetic disorders caused by recessive alleles “suddenly appear”.
- False
- Defective gene was probably there always, but if you make a zillion copies, you will have a disease
True/false: Using DNA test ing to try to remove disease genes from the breed will not make dogs healthier
True
What will happen to the genes in a breed every generation?
- They will be lost
- This will happen until the gene pool no longer has the genes necessary to build a healthy dog
If a breed looks wonderful now does that mean it’s healthy?
- 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.)
Can you improve the health of individual dogs without improving the genetic health of the breed?
- No, you must manage the health of the breed’s gene pool
Population genetics and breeding
- 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.
How did breed diversity happen so quickly?
- 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
Tameness and neuroendocrine function
- Delayed development of adult characteristics
- HPA function
- Melanin stimulating hormone receptors in hippocampus and hypothalamus
- Huge impact on phenotype by selecting the genotype
Caveats of pedigree analysis
- While helpful if you have the data, many times animals that have problems don’t have this data
Some genetic caveats to recessive and dominant
- 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
Progeny testing
- 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
Test mating unknown to homozygous recessive
- As number of normal offspring increases, your probability of being a carrier drops down significantly
- Starts at 50%
Test mating unknown to heterozygous carrier
- ame deal
- But if normal offspring is only 1, still a 75% chance of being a carrier
- doesn’t really drop down until 16
