Week 3 Flashcards
why are family studies important
determines if a disorder is hereditary
shows the method of transmission
allows genetic counselling for future chances
can sometimes provide a diagnosis
what is the law of segregation
observation that each individual has two genes for each characteristic
and only one is passed down
this logic is explained to families
what is mendelian diseases
single gene disorders
medical conditions caused by change in one or both copies of genes
what is autosomal inheritance
trait or disorder
determined by gene on an autosome
what is a sex linked inheritance
trait or disorder
determined by a gene on a sex chromosome
what is pleiotropy
where a mutation is in a single gene
can cause two or more apparently unrelated effects
often in autosomal dominant diseases
what is the autosomal dominant pattern of inheritance
50% chance of being affected
an affected individual has at least one affected parent
vertical transmission
variable penetrance
proportion of individuals with the same genetic mutation who show symptoms of that disorder
variable expressivity
range of signs and symptoms from genetic background and environment
what is anticipation
where a disorder becomes more severe with each generation
caused by a triplet repeat expansion
what is the autosomal recessive pattern of inheritance
homozygotes - needs two copies of the gene to be affected
transmission is normally in one generations siblings
horizontal transmission
what is pseudodominance
where a single recessive gene is inherited
but is still expressed
this is the result of a deletion of a masking dominant gene
what are genocopies
mutants at a different gene loci
have the same phenotype
double heterozygotes - where both parents are affected but the children are not
what is an x linked recessive disease
one altered gene on the x chromosome
as males only have one chromosome - they are always affected
x linked recessive disease chances
males always affected
mother is normally an unaffected carrier
daughters can be carriers
no male to male transmission
carrier females have a 25% chance of having an affected child
where father is affected - daughters will be carriers
x linked dominant
dominant gene carried on the x chromosome
so males and females affected equally
x linked dominant inheritance
depends on whether mother or father is the carrier
mother - 50% offspring
father - 100% daughters
what is reduced or incomplete penetrance
autosomal dominant disorders with few or no abnormal clinical features
variable expression
range of features indifferent individuals
new mutations / de novo
trait appears without any family history
homozygosity for autosomal dominant traits
usually in heterozygous state, rarely homozygous
can have different phenotypic effects
compound heterozygosity
presence of two mutated alleles at a particular gene locus
co dominance
where two alleles are expressed in the heterozygous state
