DEFINITIONS Flashcards
Define “modifier genes”.
Other, unrelated genes which have a small effect on phenotype (i.e. affecting disease severity or penetrance)
Define “variable expression” or “variable expressivity”.
Autosomal dominant disorders in which affected individuals within the same family are affected by a disease to different extents
Define “incomplete penetrance”.
When there is a less than 100% chance an individual will have the disease if they have the mutated gene
Define “complete penetrance”.
When there is a 100% chance that the individual will have the disease if they have the mutated gene
Define “gonadal mosaicism”.
Presence of both normal and mutated egg/sperm cells in unaffected adults of reproductive age
Define “compound heterozygotes”.
When the two mutations causing an autosomal recessive disease are not the same mutation (e.g. when different mutations of the same allele can cause disease)
Define “manifesting carriers”.
Carrier females who present with the disease
Define “skewed X inactivation”.
When there are more X chromosomes being switched off than there are healthy ones, resulting in manifesting carriers
Define “genetic anticipation”.
Genetic conditions in which the disease shows increasing severity and earlier onset in successive generations
Define “trinucleotide repeat disorders”.
Disorders caused by long repeats of a trinucleotide, which often get longer in successive generations
Define “pseudo-dominant inheritance”.
An autosomal recessive condition with consanguinity or a very high frequency, thus affecting people in more than one generation and appearing as an AD disorder
Define “heteroplasmy”.
Mitochondrial mutations when, out of the several chromosome copies in mitochondrial DNA, some are mutated and some are normal
Define the “threshold effect”.
The limit in the balance between normal and mutated mitochondrial chromosomes needed to cause disease
