Estimating Risk of Inherited Disease Flashcards
The frequency of alleles in the whole population affects the health of the population.
population genetics
relative ability of organisms to survive and pass on genes.
“Fitness”
Alleles can affect fitness
Do not affect fitness in most cases
Neutral Allele
Allele that decrease fitness (sometimes)
deleterious allele
Allele that increase fitness (rarely)
advantageous allele
Relative frequencies remain ….
constant
Dominant conditions (alleles) do not become more common at the expense of recessive ones!
Hardy-Weinberg equilibrium (HWE)
Allele frequencies remain constant generation to generation.
Relative proportion of genotype frequencies remain constant generation to generation.
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
Assumptions underlying HWE
Ideal Population
Mutations …… the proportion of new alleles.
increase
Introduction of new alleles as a result of …. or ……….. leads to new gene frequency in hybrid population.
migration
intermarriage
…. increase mutant alleles, thereby increasing proportion of affected homozygotes.
Non-random mating
Choosing of partners due to shared characteristics.
Assortative mating -
Marriage between close blood relatives
Consanguinity
A gradual process by which biological traits become either more or less common in a population
Natural selection
Reduces reproductive fitness. - decreases the prevalence of traits. - leads to gradual reduction of mutant allele.
Negative selection
Increases reproductive fitness. - Increases the prevalence of adaptive traits. - Heterozygote advantage.
Positive selection
Sickle Cell Anaemia, Thalassaemia and G6PD def have a ….. advantage and are resistant to..
Heterozygote advantage
Malaria
Cystis Fibrosis have a … advantage and is resistant to …..
Cholera/Typhoid
Large populations can balance out ….. , but small populations can exhibit “” and cause “”.
fluctuations
genetic drift
founder effect
Random fluctuation of one allele transmitted to high proportion of offspring by chance
Genetic drift
bottleneck effect
Mutations (alleles) 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.
The reduction in genetic variation that results when a small subset of a large population is used to establish a new colony.
founder effect
Ellis-van Creveld syndrome
Assortative mating
The syndrome is more concentrated among the Amish because they marry within their own community.
Amish of Pennsylvania (a small number of German immigrants)
Polydactyly - extra fingers
Application of HWE
calculating risk in genetic counselling
planning population based carrier screening programmes
