Extranuclear genome - University of Houston · Extranuclear genome organelles involved with energy...

Extranuclear genome

organelles involved with energy conversionmitochondriachloroplasts

formerly free-living bacteria

cells have multiple copies of each type vs. single nuclear genome

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 %%%%%%%%, &&&&&&&&

G1

G2

G3

G4

Leber’s hereditary optic neuropathy (LHON)

affected offspring have an affected motheraffected fathers never have affected children

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

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

cytoplasmic segregation(mosaic)unequal

replication

mutation

heteroplasmic

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

MERRF expression is affected by mtDNA frequency

mtDNA tissue affectedGenotype brain heart muscle skin

20% + - - -

40% + +/- - -

60% + + + -

80% + + + +

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