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Flashcards in Estimating risk of inherited genetic disease Deck (15):

Fitness of alleles

- Means the relative ability of organisms to survive and pass on genes


3 alleles fitness types

- Neutral allele: most common, not effect
- Deleterious allele: less common, sometimes decrease
- Advantageous allele: rarely increased


Population genetics definition

- Frequency of alleles in the whole population affects health of the population


Generation genotype frequency

AA:Aa:aa = p^2: 2pq: q^2


Generation allele frequency

A:a = p : q


Hardy-Weinberg Equilibrium

- Allele frequencies remain constant generation to generation
- p+q = 1
- p+q+r=1


Assumptions for an 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


Gene flow

- Mutations increase the proportion of new alleles
- Introduction of new alleles as a result of migration leads to new gene frequency in hybrid population


Non-random mating

- Leads to increase mutant alleles which leads to an increased proportion of homozygotes
- Assortative mating (partners with shared characteristics)
- Consanguinity (marriage between close blood relatives)


Natural selection

- Gradual process by which biological traits become more or less common in a population
- Negative selection
- Positive selection


Negative selection

- Reduces reproductive fitness
- Decreases the prevalence of traits
- Leads to a gradual reduction of mutant allele


Positive selection

- Increases reproductive fitness
- Increases prevalance of adaptive traits
- Heterozygote advantage
- Actively maintained in gene pool at frequencies longer than expected from genetic drift alone


Genetic drift

- Random fluctuation of one allele transmitted to high proportion of offspring by change
- Happens due to random events, not natural selection


Founder effect

- Reduction in genetic variation when a small subset establishes a new colony
- If a new colony is started by a small group with reduced genetic diversity then there will be limited genetic variation
- e.g. Amish -> Ellis-van Creveld syndrome has assortative mating so they have natal teeth and extra finger


Clinical application of HWE

- Calculating risk in genetic counselling
- Planning population based carrier screening programmes