Biochem 84 Flashcards
Define codominance
Both alleles contribute to the phenotype of the heterozygote
Examples of codominance?
1) Blood groups
2) Alpha-1 antitripsin deficiency
Define variable expressivity
Phenotype varies among individuals with same genotype
Example of variable expressivity
NF-1
Define incomplete penetrance
Not all individuals with mutant genotype show mutant phenotype
Example of incomplete penetrance
BRCA1 gene does not always result in breast or ovarian cancer
Define pleiotropy
One gene contributes to multiple phenotypic effects
Example of pleiotropy
Untreated PKU
Define anticipation
Increased severity or earlier onset of disease in succeeding generations
Example of anticipation
Trinucleotide repeat disorders (e.g. Huntingtons)
Define loss of heterozygosity
If a patient inherits or develops a mutation or deletion of a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer can occur.
note: this is not true of oncogenes
Example of loss of heterozygosity
Retinoblastoma and the “two hit hypothesis”
Define dominant negative mutation
Exerts a dominant effect.
A heterozygote produces a nonfunctional altered protein that prevents the normal gene product from functioning
Example of negative dominant effect
Mutation of a transcription factor in its allosteric site
Define linkage disequilibrium
Tendency for certain alleles at 2 linked loci to occur together more often than expected by chance.
Measure in populations not famiies
Define mosaicism
Presence of genetically distinct cell lines in the same individual
Mosaicism arises from what?
Mitotic errors after fertilization
What is the difference between somatic mosaicism and gonadal mosaicism?
Somatic: mutation propagates through multiple tissues or organs
Gonadal: mutation only in egg or sperm cells
Example of mosaicism
McCune-Albright syndrome
- lethal if the mutation is somatic, but survivable if mosaic
Define locus heterogeneity
Mutations at different loci can produce a similar phenotype
Example of locus heterogeneity
Albinism
Example of allelic heterogeneity
B-thalassemia
Define allelic heterogeneity
Different mutations in the same locus produce the same phenotype
Define heteroplasmy
Presence of both normal and mutated mtDNA, resulting in variable expression in mitochondrial inherited disease
