Estimating risk of inherited genetic disease Flashcards
Fitness =
relative ability of organisms to survive (long enough) to pass on their genes.
what can affect fitness
alleles:
- not at all in most cases (neutral allele)
- sometimes decrease (deleterious allele)
- rarely increase (advantageous allele)
Few notable common recessive diseases
- Sickle cell disease
- Thalassaemia
Mutation in recessive genes rarely affects
carriers
Mutation in dominant and X-linked genes can be
inherited or de novo
De novo mutation common in
dominant disorders esp. where disease reduces reproductive fitness
- Recently recognised as a common cause of many severe learning disability syndromes
Up to 1/3 of lethal X-Linked cases are due to
a de novo mutation
Dominant conditions (alleles) do not
become more common at the expense of recessive ones!
Relative frequencies remain
constant
Allele frequencies remain
constant generation to generation.
Relative proportion of genotype frequencies remain
constant generation to generation.
Hardy-Weinberg equilibrium (HWE) calculates
expected genotypes
Assumptions underlying 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
60% of men in northwest Scotland have
Norwegian DNA
Introduction of new alleles as a result of
migration or intermarriage leads to new gene frequency in hybrid population.
