Biochemistry - Genetics Flashcards
Allele
one of two or more versions of a gene. An individual inherits two alleles for each gene, one from each parent
Phenotype
observable traits. determined by genotype and by the environment
Genotype
genetic makeup of a cell, an organism, or an individual. An individuals genotype for that gene is the set of alleles it happens to posses
Codominance
both alleles contribute to the phenotype of the heterozygote
ex. blood groups A, B, AB; alpha1-antitrypsin deficiency
Variable expressivity
phenotype varies among individuals with same genotype
ex. 2 pts with neurofibromatosis type 1 may have varying dz severity
Incomplete penetrance
not all individuals with a mutant genotype show the mutant phenotype
ex. BRCA1 gene mutations do not always result in breast or ovarian cancer
Pleiotropy
one gene contributes to multiple phenotypic effects
ex. untreated PKU manifests with light skin, intellectual disability, and must body odor
Anticipation
increased severity or earlier onset of disease in succeeding generations
ex. huntington dz
Loss of heterozygosity
if a pt inherits or develops a mutation in a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer develops. This is not true of oncogenes
ex. retinoblastoma
Dominant negative mutation
exerts a dominant effect. A heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning
Linkage disequilibrium
Tendency for certain alleles at 2 linked loci to occur together more often then expected by chance. Measured in a population, not in a family, and often varies in different populations
Mosaicism
presence of genetically distinct cell lines in the same individual. Arises from mitotic errors after fertilization
Locus heterogeneity
Mutations at different loci can produce a similar phenotype
ex. albinism
Allelic heterogeneity
Different mutations in the same locus produce the same phenotype
ex. b-thalassemia
Heteroplasmy
presence of both normal and mutated mtDNA, resulting in variable expression in mitochondrial inherited dz
Uniparental disomy
Offspring receives 2 copies of a chromosome from 1 parent and no copies from the other parent. Heterodisomy (heterozygous) indicates meiosis I error. Isodisomy (homozygous) indicates a meiosis II error or post zygotic chromosomal duplication of one of a pair of chromosomes, and loss of the other original pair
Imprinting
At some loci, only one allele is active; the other is inactive (imprinted/inactivated by methylation). With one allele inactivated, deletion of the active allele -> disease
ex. Prader-Willi syndrome and Angelman syndrome (both chromosome 15)
Prader-willi syndrome
Maternal imprinting: gene from mom is normally silent and Paternal gene is deleted/mutated
Hyperphagia, obesity, intellectual disability, hypogonadism, and hypotonia
angelMan syndrome
Paternal imprinting: gene from dad is normally silent and Maternal gene is deleted/mutated
Inappropriate laughter, seizures, ataxia and severe intellectual disability
X - linked recessive disorders
X marks the spot! Be Wise, Fools GOLD Heeds Silly HOpe
Bruton agammaglobulinemia Wiskott-aldrich syndrome Fabry dz G6PD deficiency Ocular albinism Lesch-nyhan syndrome Duchenne muscular dystrophy Hunter Syndrome Hemophilia A and B Ornithine transcarbamylase deficiency
Trinucleotide expansion dzs
Try (trinucleotide) Hunting for My Fried Eggs (X) Huntington dz Myotonic dystrophy Friedreich ataxia Fragile X syndrome
Trinucleotide repeat expansion dz disorders
X-Gfs First Aid Helped Ace My Test Fragile X syndrom - CGG Fredreich ataxia - GAA Huntington dz - CAG Myotonic dystrophy - CTG
