Bio 240 Chapter 9 notes
Bio 240 Chapter 9 notes Bio 240
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This 4 page Class Notes was uploaded by Izabella Nill Gomez on Sunday October 18, 2015. The Class Notes belongs to Bio 240 at University of Tennessee - Knoxville taught by Dr. Hughes in Summer 2015. Since its upload, it has received 16 views. For similar materials see General Genetics (Bio 240) in Biology at University of Tennessee - Knoxville.
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Date Created: 10/18/15
Biology 240 chapter 9 Notes With advancing research extranuclear inheritance is a recognized aspect of genech Organelle heredity DNA contained in mitochondriachloroplasts determines the phenotypic characteristics of the offspring Ex uniparental transmission usually is from the female through the egg to progeny Infectious heredity symbiotic or parasitic association with the microorganism The phenotype is affected in the cytoplasm of the host cells Maternal effect nuclear gene products are stored in the egg and transmitted through the cytoplasm of the offspring Gene products are distributed to cells of the developing embryo and in uence the phenotype What do they share in commoninformation is transmitted through the cytoplasm not the nucleusextranuclear inheritance Anaysis of mutant alleles from chloroplastsmitochondria is dif cult because the function of organelles is dependent on gene products from nuclearorganelle DNA Also the organelles contributed to each progeny cell follows cell division Heteroplasmy variation of genetic content in organelles Car Correns provided evidence linking inheritance by chloroplast transmission in Mirabiisjaapawith green and white leaves The white leaves did not have chlorophyll Inheritance of the chloroplast is determined in the cytoplasm of the maternal parent because pollen contributes little cytoplasm has no effect on the zygote Choroplast mutations in Chlamydomona5has single large chloroplast with 75 circular DNA copies DNA that contributes resistance to antibiotics was passed onto the female parent mt The genes depended on the mother Linked to transmission of the chloroplast When mating fuses both for the zygote genes are derived from the motherinheritance is uniparental But mt the father determines the mitochondrial information Mitochondrial mutations are transmitted through the cytoplasm during reproduction Ex poky mutant in Neurospora crassa bread moldSlow growth is associated with the poky mutation and impaired mitochondrial function due to lack of cytochrome proteins essential for electron transport The strain is maternally inherited Another example is yeast and mutational variants from mitochondria de ciency in cellular respiration due to abnormal ETC Creates petites that become facultative anaerobes to survive Segregational petites exhibit Mendelian inheritance neutrals yield only wild type and suppressives give rise to diploid zygotes that after meiosis become haploid for poky petite Petite cells that inherit both wild and polq mitochondria express dominantnegative mutations which suppress the wild type function A possible explanation suggests mutant or deleted DNA in mitochondria mtDNA replicates more rapidly resulting in mutant DNA taking over or dominating the phenotype by numbers alone Another suggestion is that recombination between mutant and wild types brings errors to the normal mtDNA Endosymbiotic theory theory that mitochondria and chloroplasts arose independently about 2 billion years ago as freeliving bacteria The cells were engulfed by primitive eukaryotic cells and entered a symbiotic relationship The bacteria could no longer live autonomously and the eukaryotic host gained the ability to perform oxidative respiration or photosynthesis During the evolution of host cells the symbiont bacteria also underwent independent changes The primary alteration was the transfer of genes from the bacterium to the host cell nucleus The products are now encoded and transcribed in the nucleus and translated into the cytoplasm before moving into the organelle DNA in mitochondria is tiny compared to ancient bacteria Similar occurred in chloroplasts Choropasts have 2 functions Capture light energy and split water C02 is xed into sugars Choropast DNA chNA is fairly uniform among different organisms from 100225 kb in length Similar to DNA in prokarya Circular double stranded no proteins Size of chNA is larger than mtDNAthe difference is due to the long noncoding sequences between and within genes introns chNA encodes numerous tRNAs and ribosomal proteins speci c to chloroplast ribosomessimiar to bacterial For mtDNA introns are usually absent from the mitochondrial genes and repetitions are not usually present Human mtDNA encodes 2 rRNAs and 22 tRNAs and 13 polypeptides essential to respiration of the organelle ln vertebrate DNA the 2 strands vary in density The majority of proteins functioning in the mitochondria are encoded by nuclear genes ex DNA and RNA polymerases initiating and elongating factorsetc Distinct form the cytoplasmic counterparts even though they are encoded in the same place mtDNA is susceptible to mutations because 1 It does not have protection form mutations provided by histone proteins present in nuclear DNA 2 DNA repair for mtDNA is limited and 3 Mitochondria concentrate highly mutagenic reactive oxygen species ROS generated by respirationin con ned space it is highly toxic and can damage proteins lipids and mtDNA In order for a human disorder to be attributed to mutant altered mitochondria 1 Inheritance must exhibit a maternal pattern 2 The disorder must re ect the de ciency in bioenergetics function of the organelle 3 There must be a mutation in 1 or more of the mitochondrial genes Today there are over 150 syndromes related to mitochondrial dysfunction Myclonic epilepsy and raggedred ber disease MERRF demonstrates maternal inheritance and offspring of affected fathers are normal The affected express ataxia deafness dementia and epilepsy Related to a mutation in one of the twenty two mtDNA encoding tRNAs Reveals patterns of heteroplasmy Without heteroplasmy the mutation would be lethal in the affected Leber39s hereditary optic neuropathy LHON the affected exhibit maternal inheritance and mtDNA lesions Characterized by sudden blindness Average age for this is 27due to disruption of oxidative phosphorylation No family history is usually involved tends to be sporadic KearnsSayre syndrome KSS loss of vision hearing and heart conditions Involves deletions of mtDNA mitochondria disorders also seem to play a role in almost all major conditions including type II diabetes autism atherosclerosis infertility Parkinson s Alzheimer39s Huntington s and some cancers Also involved in aging due to a decrease in ATP production for cells or deletionsmutations in mtDNA Transpants of nuclear genomes can now prevent mtDNA mutations for offspring eliminating the risk for disorders lnvolves the rhesus monkey genome implanted in the egg of the mother and is fertilizedmitochondrial swapping Still pending legal approval In maternal effect the genotype of the female parent not the embryo determines the phenotype of the offspring Possible Exam questions lnheritance of green and white leaves in Mirabilis jalapa is due to maternal in uence FALSE Shell coiling in Lymnea peregra is in uenced by due to maternal effect orientation of the spindle apparatus early in cleavage One explanation for organelle inheritance is that mitochondria and chloroplasts are subject to DNA mutation Future nuclear transplantation might be available to treat mtDNA disorders This is known as mitochondrial swapping
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