Non-Mendelian Patterns and Epigenetics

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inherit both chromosomes of a homolog from same parent
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Terms in this set (35)
inherit both chromosomes of a homolog from same parent
uniparental disomy
difference between hetero and isodisomy
heterodisomy: 2 different homologs of same chromosome
isodisomy: same homologs of same chromosome
what is trisomic rescue
fetus originally trisomic followed by loss of chromosome leading to normal disomic state
what is nondisjunction
when sister chromatids do not separate
epigenetic modification of DNA involving differential expression of alleles of a gene in somatic cells
genomic imprinting
disease leading to compulsive overeating, hypotonia, mental retardation and short stature
Prader-Willi Syndrome
causes of prader-wili syndrome
-70%: deletion of 15q12 on paternally derived chromosome
-25%: uniparental disomy (both chromosomes from mom)
-5%: imprinting center error
disease with severe mental retardation, inappropriate laughter, seizures, jerky gait
Angelman Syndrome
cause of Angelman Syndrome
-70%: maternal deletion inf 15q
-5%: imprinting error
-15-25%: Gene mutation UBE3A
-5%: Uniparental disomy (both chromosomes from dad)
mitosis characteristics (somatic cells)
-1 replication and 1 division phase
-DNA/Chromosome replication gives rise to identical sister chromatids
-produces daughter cells that are genetically the same as each other and parental cell
-homologous chromosomes typically don't pair
when do sister chromatids separate in mitosisduring division phasephases of mitosis-prophase -metaphase -anaphase -telophase -cytokinesisMeiosis characteristics (gametes)-one replication phase and 2 division phases -DNA/chromosome replication gives rise to identical sister chromatids -final products have 23 chromosomes -homologous chromosomes pair and then separate to opposite poles in first divisionwhen do sister chromatids separate in meiosissecond divisionDoes genetic recombination occur between homologs in meiosis-yes -exchange of material in meiosis I (if not recombination can lead to problems) which helps then alignHow does UPD happen-sometimes meiotic erros -usually fetus originally trisomic and then lose a chromosome to become disomicform of gene marking thats reversiblegenomic imprintingcan epigenetic mark be heritable?yes -imprintingT/F: genomes inherited from mom an dad are not functionally equivalenttrue (imprinting)why get PWS still if normal chromosome derived from mom-imprinting: mothers genes are shut off -Need normally expressed genes in Chr15 of dad to not have PWSPWS recurrence risk-deletions and UPD: less than 1 percent (usually de novo deletions and UPD rare) -Imprinting error: can be 50% (error may be heritable mutation present in parent)whats UBE3A (E6-AP)ubiquitin protein ligase gene on chromosome 15 (mutated in angel man sometimes)imprinting mechanism-occurs before fertilization -confers txn silencing of maternal or paternal allele -stable when transmitted through mitosis in somatic cells -must be reversible on passage through opposite sex -can impact inheritance patternDNA that codes for some genes important for mitochondria function and oxidative phosphorylationmtDNAinheritance of mtDNA-maternal inheritance (diseases from mutated mtDNA passed from female to offspring only)mutation rate of mtDNA10-100x greater than nucleus due to lack of proofreading and DNA-repairmtDNA diseases-disorders of ox.phosphorylation, FA oxidation, etc -LHON (leber hereditary optic neuropathy) -MERRF (myclonic epilepsy with ragged red fibers) -MELAS (mt encephalomyopathy, lactic acidosis and stroke-like episodes) -Leigh Syndrome and NARP (later in life) -Deafnessmost common clinical finding for mtDNA diseasesneurologic problemcauses of mtDNA diseases-Genetic defects (point mutations, deletions, duplications, etc) -De novo mutations (no family history) -Accumulation of mutations with age (high mutation rate and low repair)whats homoplasmy and heteroplasmy in mtDNAHomoplasmy: MtDNA genomes of cell the same heteroplasmy: MtDNA genomes more than one type (ex: mutant and wild type)how is mtDNA sortedrandomly -then cell divides and mt distribute randomly between 2 daughter cells (replicative segregation)threshold effect in mtDNA-if end up with many mutant mitochondria may see phenotypic expression -depends on tissue -phenotype may vary with timewhat does threshold effect lead to-Reduced penetrance -variable expressivity -pleiotropygenetic bottleneck-heteroplasmic females transmit some mutant mtDNAs - # mtDNA reduced then amplified in mature oocyte (bottleneck) -can lead to variability in % offspring with mutant mtDNAleber hereditary optic neuropathy (LHON)-blindness due to optic nerve atrophy (mainly central vision) -visual acuity reduced -most people have point mutation of mtDNA (largely homoplasmic) -complicated by gender and age dependent penetrance