Class Note for ECOL 320 at UA
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Date Created: 02/06/15
Section 17 Organelle Genetics Genetics of Mitochondria and Chloroplasts Flourescence micrograph of alga Olisthodiscus Chlorophyll autofluoresces red DNA stained with DAPI fluoresces white OChloroplasts and chNA 0Mitochondria and mtDNA ONucleus and nuDNA Yeast mitochondria Chlamydomonas chloroplast Tony Linnane David Wilkie 39 Nick Gillham Originated as intracellular symbionts Eukaryotic cell phagocytosis of alphaproteobacteriumgt cell symbiont genes lost or transferred to nucleusgt cell mitochondria Cell mitochondrion phagocytosis of cyanobacterium cell symbiontgenes lost or transferred to nucleus cell chloroplast In subsequent evolution mito and cp retained some traits of their symbiotic ancestors selfreplication 0 some genes proteinsynthesizing machinery BUT organelles never evolved mechanism to ensure that every copy of the genome replicated once per cell cycle mitotic apparatus to partition copies They never evolved the machinery necessary for Mendelian inheritance Mitochondria and chloroplasts are selfreplicating organelles They are produced only by growth and division of preexisting mitochondria or chloroplasts They cannot be formed de novo or from other organelles or proexisting membranes They grow by the insertion of molecules in to their membranes ESE RE l 4 t l f l l am my life1 pi a Mitochondria and chloroplasts contain DNA genomes with a small number of functional genes mitochondrial DNA mtDNA chloroplast DNA 2 chNA 0 Very few genes remain from the symbiont ancestors Compare and contrast to nuclear genes orders of magnitude number of genes eukaryote nuclear genome 104 105 euk mitochondria amp chloroplasts 40 102 prokaryote cell genome 500 104 C value in kbp 104 108 1 102 500 104 Number of genes ranges from 37 genes in human mito to 130 genes in plant mitochondria Most proteins and all lipids etc in organelles are synthesized in the cytoplasr imported Genes required for aerobic respiration electron transport mitochondria and photosynthesis chloroplasts Organelle genomes almost always have all their genes on a single circular DN molecule Each cell contains many organelle DNA molecules order of 102 104 more in big eggs hence many copies of each gene These are packaged in 1 103 organelles more in big eggs 551 210 ZI 39l ElJD le I 39 39 LL ul 9 C3 L W O l J J lira L39 x a eg alga Chlamydomonas haploid ca 100 chNA molecules in one chloroplast eg yeast ca 50100 mtDNA molecules in 1 to 50 mitochondria depending on genotype and physiological state of cells mito fuse and divide eg mammalian cells in culture ca 103 mtDNA molecules in several hundred mitochondria 1909 Erwin Baur and Carl Correns found first cases of nonMendelian heredity in plants But only Baur interpreted them correctly Pelargonium geranium Studied inheritance of wild type green and mutant white no chlorophyll no photosynthesis variegated leaves Violated two of Mendel39s laws Some plants inherited genes from only one parent usually female sometimes male Alleles segregated during vegetative asexual growth Laws of Organelle Genetics Vegemive segregation alleles of unmnsnmmmme organelle genes segregate during mitotic as well as meiotic X dmmm mquot J We Uniparenml inheritance organelle mm mm genes are often transmitde from quotquot2 quotquot2 only one parent i M st of Vegetauve vsemms ssensemon Seg39reganon Many copies of genome per cell and per organelle Genomes seleaed ca randomly for vegetatwe replicauon so some may replncave heteruplasmvc meme humuwsmv morethanothels 2va 2 M5 Genomes partitioned ca randomly Wm when organelle divides 4 Organelles partitioned ca randomly when cell divides harnaplaemie heteraplaemic plastin in plaetids in heteraplasmic heteraplasmie cell cell mutatian relaxed relaxed replieatian partitioning af chN of epDNfi Ira S a r a t 39 i E quot gt lt 0 1 II a 0 WI I 39 39 39 k9 I H Jquot stringent m relaxed reiaxeu nameplaarnie DlElEtlEIS partitioning in replication Elf BEENd3 or plastiljs nameplasmic cell MECHANISMS OF VEGETATIVE SEGREGATION Homoplasmic cell organelle or organism has only one allele of an organelle gene cf homozygous Heteroplasmic cell organelle or organism has 2 2 alleles of an organelle gene cf heterozygous Alleles in heteroplasmic cell can be in different proportions frequencies eg 1100 23100 etc 0 Random replication Organelle DNA molecules are selected randomly stochastically for replication so one allele often replicates more than the other just by chance 0 Random partitioning of genomes When organelle divides genomes partitioned randomly with respect to genotype so one or both organelles are often homplasmic 0 Random partitioning of organelles When cell divides organelles are partitioned randomly between daughter cells so one or both daughters are often homoplasmic Intracellular random genetic drift Thrailkill Birky Liickermann and Wolf 1980 mitochondria Birky et al 1981 chloroplasts random changes in allele frequencies in cell Intracellular selection Birky 1973 Some molecules can replicate more often than others not only by chance but also because they are smaller and can replicate faster or because they confer increased fitness on their mitochondria homoplasmic homoplasmic White green 00 am co 8383 homoplasmic green O 0 COO When all cells are homoplasmic expected ratio homoplasmic greenzhomoplasmic White 31 Frequency green genomes fG 075 fW 025 homoplasmic homoplasmic White green homoplasmic green O 0 COO Intracellular selection for green plastids replication stochastic not strictly random Red outcomes favored fGO gt 075 Uniparental Inheritance Inheritance in animals and many plants is exclusively from female parent therefore often called maternal inheritance But this isn39t the way to state a general rule of organelle inheritance uniparental inheritance is better LINIF39 FdENTAL INHERITANCE IN ANIMALS AND PLr uHTS E l g mg m H DNA green wmte germ QEr m HE FIE i UPI HAS MANY MECHANISMS No organelles in gamete Organelles Input bias Mixture excluded random replication 6 Ir 6 gildte Q 15 39l l v 25 l l Eli39sJ Lth 5439quot I wu Maternal 4 tr l a l figIquot 39 515 Paternal Maternal Rando partiti ing Se ct1ve s11en01ng Extraembryonic a 35 deg dation tissue 139 1 Embryo Maternal Paternal Maternal Selecljve silencing in Chhmydomona reinhardtii Sager reciprocal crosses using chNA gene demrmining sensiljvity Vs resismnce m suepmmycin m trrr x m 5m all mmds 2 mr 2 m most telmds 4 rrrr 0 my m 51H x m trrr all ends 2 mt 2 mr most telmds 4 my 0 trrr Pusamvzemmr p quotmm mum m almmz he mst m sum mm Max gm l m mm W mm mm s mm mm m Vaerenml zmxm u andlluvazem musesmmumugmsmmsysmmm m Draevenual dlnvveaunze areshuvn Yodmlngulthemr and mr39 Mam ms will mr gametawue m mum mew nun Ind mr Wm zhlamvlms m mlmng led 1mmlumaewze all quotuses my D mm lle Humanequot gm llrgumvl 1nd swans nuzleolds mu Qluaravem ms mu anle H m mums wrlh svsx mam gummy me p mm m me my Wampum m We muss swam mumle m mm mm MITOCHONDRIAL DISEASES A number of inherited diseases in humans aredue to mitochonrial mutations Homoplasmic mutant cells with only mutant mito genomes areunablew do aembic mspiration so they die Heteroplasmic cells survive but have reduced respiration gt defects in tissues mquiring hi level of mspiration eg muscle eye Mitochondrial mumtions may be involved in aging MITOCHONDRIAL GENES USED TO TRACK HUMAN GENEALOGIES Described in text will discuss after Spring Break memu murrs SUSAN mm39 HAPLnaRnuP H quot rmWm ahmnmmmummwmm NATIONAL GEOGRAPHIC SUMMARY Organelle genes differ from nuclear genes 0 Many copies per organelle and per cell homoplasmic or heteroplasmic allele frequencies 0 Replication random With respect to genotype but final number counted unless have intracellular selection 0 Partitioning of genomes and organelles random stochastic With respect to genotype Organelle genes don t obey Mendel s laws 0 Vegetative segregation 0 Uniparental inheritance maternal in humans and most other animals
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