Estimating risk of inherited genetic disease Flashcards
Fitness
Relative ability of organisms to survive and pass on genes
What does fitness depend on?
Types of alleles eg neutral, deleterious or advantageous
Do deleterious mutations sometimes or rarely decrease fitness?
Sometimes
Do advantageous mutations sometimes or rarely increase fitness
Rarely
Frequency of alleles affect healthy population
Population genetics
1 gene with 2 alleles what are p and q
p = dominant q = recessive
Genotype frequency
GG/total
Allele frequency
Gt/ total alleles ( NB double the number as alleles separate)
Do dominant conditions become more common at the expense or recessive alleles?
NO
Hardy-Weinberg principle
Use quadratics
What are constant generation to generation?
Allele frequency and relative proportion of genotype frequency
p squared = q squared = 2pq=
1
What can HWE allow?
Calculate risk in genetic counselling
Plan population based carrier screening programmes
p squared
Homozygous dominant
q squared
Homozygous recessive
pq
Heterozygous
When is HWE not always achieved?
Blood type
Name some characteristics of an ideal population
- Mutation can be ignored and migration is negligible
- Mating is random and there are no selective pressure
- Allele frequency equal in sexes in large population
Do mutations increase or decrease proportion of new alleles?
Increase
What else increases the proportion of new alleles?
Migration and intermarriage
Give an example of migration and proportion of alleles
60% of men in NW Scotland have Scandinavian DNA and leads to a hybrid population
What does non random mating do?
- Increase mutant alleles
- Increase affected homozygotes
Assorative
Shared characteristic
Consanguinity
Close blood relatives
Natural selection
Gradual process where traits become more or less common in a population
Negative natural selection
Reduces reproductive fitness
Decrease prevalence of traits
Gradual reduction of mutant allele
Positive natural selection
Increases reproductive fitness
Increase prevalence of adaptive traits
Heterozygote advantage
Give some examples of heterozygote advantage
Cholera/ typhoid with CF
Sickle cell anaemia for malaria
G6PD for malaria
What do large populations do to fluctuations?
Balance them out
Genetic drift
Random fluctuation of one allele to high proportion of offspring - mutations widespread and neutral after a fire or ploughing etc
Founder effect
Genetic drift causes this reduction in genetic variation when a small subset of large population establish new colony with limited variation eg Amish founded from a small number of German immigrants
Bottleneck effect
Reduce genetic diversity
Assortative mating
Polydactyl common in Amish due to intermating
