Estimating Risk of Inherited Genetic Disease COPY Flashcards
What is meant by fitness?
The relative ability of organisms to survive and pass on genes
What is an allele that increases fitness?
Advantageous allele
What is a neutral allele?
Doesn’t effect fitness
What is a deleterios allele?
A decrease in fitness - causes disease
What affects the health of the population?
The frequency of alleles
Do dominant alleles become more common from generation to generation?
No, relative frequencies remain constant
genotype frequencies also remain constant
dominant alleles dont become more common at the expense of recessive ones
What are the assumptions underlying the HWE?
IDEAL POPULATION
- Mutation can be ignored
- Migration is negligible (No gene flow)
- Mating is random
- No selective pressure
- Population size is large
- Allele frequencies are equal in the sexes
What does the introduction of new alleles as a result of migration or intermarriage leads to?
New gene frequency in hybrid population.
What is the result of non-random mating?
Leads to increase mutant alleles, thereby increasing proportion of affected homozygotes
What is the choosing of partners due to shared characteristics?
Assortative Mating
What is Consanguinity
Marriage between close blood relatives.
What is natural selection?
A gradual process by which biological traits become either more or less common in a population.
What is Negative selection?
- Reduces reproductive fitness.
- decreases the prevalence of traits.
- leads to gradual reduction of mutant allele
What is positive selection?
- Increases reproductive fitness.
- Increases the prevalence of adaptive traits.
- Heterozygote advantage.
What is the effect of small population?
Can exhibit “genetic drift” and cause “founder effect”.
What is meant by genetic drift?
Random fluctuation of one allele transmitted to high proportion of offspring by chance.
mutations are widespread and neutral, statistical drift of gene frequencies due to chance or random events rather than natural selection in the formation of successive generations
What is the founder effect?
The reduction in genetic variation that results when a small subset of a large population is used to establish a new colony.
What is the bottleneck effect?
Catastrophe results in a population with a high expression of a certain phenotype, regardless of wether or not it is advantageous to the population
recessive mutation and disease
- mutation in recessive genes rarely affects carriers
- where it does it is often associated with a selective pressure
- de novo recessive mutation is uncommon as a cause of disease
dominant mutation
de novo mutation is common in dominant disorders
up to 1/3 of lethal X-L cases are due to a de novo mutation
applications of HWE
- calculating risk in genetic counselling
- planning population based carrier screening programmes
