Genetics words Flashcards
Codominance
- Both alleles contribute to phenotype
- Ex: blood types A, B, AB; a1-antitrypsin deficiency; HLA groups
Variable expressivity
Different phenotypes of same genotype
Incomplete penetrance
All or nothing: individuals with same genotype either express it or nothing at all
Pleiotropy
One gene has multiple phenotypic effects
Anticipation
Incr. severity of disease in successive generations (sometimes this is all they’ll give you)
Loss of heterozygosity
- Must lose both copies of e.g. tumor suppressor gene before cancer develops (this is not true for proto-oncogenes
- I.e., the “two-hit hypothesis” (Li Fraumeni, Retinoblastomas, Lynch syndrome)
Dominant negative mutation
Heterozygote expression of one mutated, dysfunctional gene product inhibits function of normal protein
Linkage disequilibrium
- 2 linked loci occur together more or less often than by chance alone
- Only able to measure this in populations, not families
Mosaicism
Presence of distinct cell lines in same individual:
- Somatic: mitotic errors after fertilization
- Germline (aka gonadal): mosaicism in sperm or egg cells (suspect when parents have affected children even though they’re unaffected)
- Ex: McCune-Albright syndrome is survivable only if mosaic
Locus heterogeneity
Multiple loci lead to same phenotype (example = albinism)
Allelic heterogeneity
Multiple mutations at same gene lead to same phenotype (example = beta thalassemia)
Heteroplasmy
Variable expressivity + mitochondrial inheritance
Uniparental disomy
Both chromosomes from the same parent:
- Heterodisomy: meiosis I error
- Isodisomy: meisosis II error; inappropriate postzygotic chromosomal duplication, and the complement chromosome from the other parent disappears (consider when child expresses recessive phenotype with only 1 carrier parent)
- Ex: Prader-Willi, Angelman syndromes
Imprinting
One gene is silenced via methylation, and the other is expressed in a parent-of-origin manner (this is also Prader-Willi and Angelman)
