intro to genetics Flashcards
what is genetic counselling
communication of information and advice about inherited conditions and involves taking history and making pedigree trees
examination, diagnosis, counselling, and follow up
familial risks
what is the incidence of the disorder in relatives compared with the incidence in the general population
families share similar environments so familial aggregation does not prove genetic causation
twin studies
what is the incidence of the phenotype in monozygotic compared with dizygotic twins
if a disease is caused entirely by environmental factors, then identical and non-identical twins will have the same concordance rate
liability threshold model
shows the distribution of all risk factors in general population and the distribution and the distribution of family members of affected individuals in 2 separate curves
the shift towards higher risk means that more individuals will cross the liability threshold for having the trait
therefore there is family clustering for polygenic and multi-factorial traits
what is Huntington disease
a classic single gene disorder inherited as an autosomal dominant trait
mutation has a high penetrance and the mutation mechanism is associated with anticipation
what is penetrance
the chance that a genotype results in the associated phenotype
what is anticipation
signs and symptoms of the condition become more pronounced as the condition is passed from one generation to the next
what is haemochromatosis
autosomal recessive disease caused by the absorption of too much dietary iron which accumulates in the liver and heart
caused by single nucleotide polymorphisms resulting in a codon change for amino acids
most patients are homozygous for the variant
what is autosomal dominant inheritance
affected person has an affected parent
occurs in every generation
child of a carrier parent has a 50% chance of inheriting gene and therefore disorder
what is autosomal recessive inheritance
both parent of affected are carriers
not always in every generation
25% of inheriting the phenotype
50% chance of being carrier
what is x linked recessive inheritance
males more frequently affected
usually an affected male in each generation
if mother is a carrier - son has 50% chance of expressing phenotype whereas daughter will only be a carrier at worst
what is x linked dominant inheritance
females more frequently affected
can have affected males and females in each generation
daughter has 50% chance of inheriting chromosome from mother, 100% chance from father
son has 50% chance of inheriting mutation from mother, 0% from father
what is mitochondrial inheritance
affects males and females but only passed on by females
sperm mitochondria reduce in quality after fertilisation
can appear in every generation
25% of inheriting with carrier mother
polygenic inheritance definition
where a phenotype is determined by multiple genes at different loci
