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single gene disorder
the genetic abnormality is the sole cause of disease
multifactorial disease
genetic variations interact with a wide variety of other factors leading to disease
chromosomal disease
-abnormal # of chr. or abnormal chr. structure
mitochondrial disease
rare type of disorders caused by mutations in non-chromosomal mtDNA
mutations and disease (same gene diff disease)
-~10,000 disease attributed to mutations in ~6000 genes
-more diseases attributed to mutations in single genes
-diff mutation in 1 gene+ diff diseases in same gene (heterogenety)
e.g mutation in FGFR-3
An example:
Mutations in FGFR-3
P250R – Muenke’s syndrome
G308R – Achondroplasia
(dwarfism)
mutations and disease (many genes 1 disease)
e.g
Xeroderma pigmentosum (XP)
‘Children of the Night’
Mutations in 8 different genes that all function in DNA-damage repair lead to XP (8 variants)
Individuals are hypersensitive to sunlight and often develop carcinomas
what is penetrance
-The frequency with which a person manifests the gene that they possess
-Not all dominant mutations display 100% penetrance
-Penetrance is determined via genetic and environmental factors
what is expressivity
Variation in the severity of the symptoms caused by a mutation
For example, in sickle cell anaemia (which is always caused by the same mutation) symptoms range from very severe to extremely mild
what's a phenocopy
An environmental modification that mimics a genetic disease
The classic example of this is confusing genetic deafness with deafness caused by Rubella during pregnancy
what is mosaicism
Not all the cells in the body are genetically identical
Two or more populations of cells with different genotypes
In the germline or somatic
Caused by mutations – different genes
Often confused with X-inactivation
An example of true mosaicism is mild Klinefelter’s syndrome (46/47 XY/XXY)`
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