extranuclear genome - university of houston · extranuclear genome organelles involved with energy...
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Extranuclear genome
organelles involved with energy conversionmitochondriachloroplasts
formerly free-living bacteria
cells have multiple copies of each type vs. single nuclear genome
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non-mendelian inheritance
uniparental – usually maternal
leakage -- contribution from paternal genome
rough wings in Drosophila melanogaster
P0 rough %%%% x wild &&&& wild %%%% x rough &&&&
F1 wild %%%%%%%%, &&&&&&&&
F2 wild %%%%%%%%, &&&&&&&& rough %%%%%%%%, &&&&&&&&
F1 rough &&&& x wild %%%% from P0 (backcross)
rough %%%%%%%%, &&&&&&&&
rough %%%%%%%%, &&&&&&&&
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G1
G2
G3
G4
Leber’s hereditary optic neuropathy (LHON)
affected offspring have an affected motheraffected fathers never have affected children
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non-mendelian inheritance
uniparental – usually maternal
leakage -- contribution from paternal genome
most individuals are homoplasmic-- one kind (genetically) of mitochondria
heteroplasmic individuals have more than one type-- arise by mutation or leakage
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mutation
heteroplasmic
homoplasmic
non-mendelian inheritance
uniparental – usually maternal
leakage -- contribution from paternal genome
most individuals are homoplasmic-- one kind (genetically) of mitochondria
heteroplasmic individuals have more than one type-- arise by mutation or leakage
replication in heteroplasmic individuals may involveunequal replication and sorting-- daughter cells that differ from parent
-- mosaicism-- phenotype of offspring
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cytoplasmic segregation(mosaic)unequal
replication
mutation
heteroplasmic
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G1
G2
G3
MERRF: Myoclonic Epilepsy and Rough Red Fiber disease
% mutantmtDNA
94 94 97 73 96 96 85 0 90 0 0
amplification/reduction of mutant mtDNA
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MERRF expression is affected by mtDNA frequency
mtDNA tissue affectedGenotype brain heart muscle skin
20% + - - -
40% + +/- - -
60% + + + -
80% + + + +
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mitochondria and chloroplasts have unique genomes that reflect their originsas free-living prokaryotes
organellar genomes are much smaller than those of free-living prokaryotes
many copies of each organelle occur in a cell, copy number may vary withinan individual
mitochondrial genes are usually inherited maternally
replicate irregularly and sometimes unequally (suppression); heteroplasmicindividuals may have considerable heterogeneity among tissues
phenotypic expression may depend on the frequency of a particular allele in the cell