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CHAPTER 20 – ORGANELLE DNAThe Donkey: A Wild Ass or a Half Ass?- Mitochondrial DNA (mtDNA) – the DNA possessed by the mitochondria that codes for some of the proteins and RNA molecules found in the mitochondria- Advantages of mtDNA for studying evolutionary relationships:o The length of mtDNA is much less than the length of DNA in the chromosomeso mtDNA is abundanto mtDNA in animals tends to evolve more rapidly than nuclear DNAo mtDNA is typically inherited from only one parent, so its genes are notreshuffled every generation by recombination- Chloroplast DNA (cpDNA) – DNA contained by chloroplastsThe Biology of Mitochondria and ChloroplastsMitochondrion and Chloroplast StructureThe Genetics of Organelle-Encoded Traits- Uniparental inheritance- Heteroplasmy – the occurrence of two distinct varieties of DNA within the cytoplasm of a single cell- Replicative segregation – when a heteroplasmic cell divides and the organelles segregate randomly into the two progeny cells- Homoplasmy – when a cell has just mutant or just wild-type sequencesThe Endosymbiotic Theory- Endosymbiotic theory – mitochondria and chloroplasts were once free-living bacteria that became internal inhabitants of early eukaryotic cells- Mitochondria and chloroplasts are membrane-bounded organelles of eukaryotic cells that generally possess their own DNAMitochondrial DNA- In animals and most fungi, mtDNA is a single, highly-coiled, circular DNA molecule- In plants, mtDNA is a complex collection of multiple circular DNA molecules- mtDNA lacks histone proteins- Mitochondrial gnomes are small compared with nuclear genomes and vary greatly in size among different organismsThe Gene Structure and Organization of mtDNA- The mitochondrial genome typically encodes only a few rRNA and tRNA molecules needed for mitochondrial protein synthesis- Ancestral and derived mitochondrial genomes- Human mtDNAo D loop – a region of the H strand that contains the origin of replicationand promoters for both the H and the L strands- Yeast mtDNA- Flowering-plant mtDNANonuniversal Codons in mtDNA- Exceptions to the universal code exist in mitochondrial DNA- These exceptions differ among organismsThe Replication, Transcription, and Translation of mtDNA- The processes of replication, transcription, and translation vary widely among mitochondrial genomes and exhibit a curious mix of eubacterial, eukaryotic, and unique characteristicsThe Evolution of mtDNA- All mtDNA appears to have evolved from a common eubacterial ancestor, butthe patterns of evolution seen in different mitochondrial genomes vary greatly- Vertebrate mtDNA exhibits rapid change in sequence but little change in gene content and organization, whereas the mtDNA of plants exhibits little change in sequence but much variation in gene content and organizationModel Genetic Organism: The Yeast Saccharomyces cerevisiae- Advantages of yeast as a model genetic organismo It is a eukaryotic organismo It is unicellularo Require little spaceo Large numbers can be grown easily and inexpensivelyo Exists in both diploid and haploid formso All of the products of a meiotic division are present in a single structure called an ascus and remain separate from the products of other meiotic divisionso Tetrad – the four cells produced by a single meiotic divisiono Tetrad analysis – the genetic analysis of a tetrado Yeast cells possess many of the genes found in humans and other complex multicellular eukaryotes- Life cycle of yeast- Genetic techniques with yeastChloroplast DNAThe Gene Structure and Organization of cpDNA- Most chloroplast genomes consist of a single, circular DNA molecule not complexed with histone proteins- Although there is considerable size variation among species, the cpDNAs found in most vascular plants are about 150,000 bp- Genes are scattered in the circular chloroplast genome, and many contain introns- Most cpDNAs contain a large inverted repeatThe Replication, Transcription and Translation of cpDNA- Many aspects of the transcription and translation of cpDNA are similar to those of eubacteriaThe Evolution of cpDNA- Chloroplast DNA sequences are most similar to DNA sequences in cyanobacteria, which supports the endosymbiotic theory- Most cpDNA evolves slowly in sequence and structureGenome ComparisonsThe Intergenomic Exchange of Genetic InformationMitochondrial DNA and Aging in Humans- CHAPTER 21 – ADVANCED TOPICS IN GENETICS: Developmental Genetics, Immunogenetics, and Cancer GeneticsFlies with Extra EyesDevelopmental Genetics- Totipotent – having the potential to develop into any type of cell- Determination – the process by which a cell becomes committedCloning Experiments- Most animal cells contain a complete set of genetic information during development- Cloning experiments demonstrate that genetic material is not lost or permanently altered during developmento Development must require the selective expression of genesThe Genetics of Pattern Formation in Drosophila- The development of the fruit fly- Egg-polarity geneso Egg-polarity genes – play a crucial role in establishing the two main axes of development in fruit flieso Morphogen – a protein whose concentration gradient affects the developmental fate of the surrounding region- Determination of the dorsal-ventral axis- Determination of the anterior-posterior axis- Segmentation geneso Segmentation genes – control the differentiation of the embryo into individual segmentso Three groups: Gap genes – define large sections of the embryo- Mutations in these genes eliminate groups of adjacent segments Pair-rule genes – define regional sections of the embryo and affect alternate segments Segment-polarity genes – affect the organization of segments- Mutations cause part of each segment to be deleted and replaced by a mirror image of part or all of an adjacent segment- Homeotic geneso Homeotic genes – determine the identity of individual segments Products activate other genes that encode these segment-specific characteristics Mutations cause body parts to occur in the wrong segmentso Homeobox – contained in each homeotic gene, consist of 180 nucleotides, encode 60 amino acids that serve as a DNA-binding domaino Two major clusters: Antennapedia complex – affects the development of the adult fly’s head and anterior thoracic segments- Comprises five genes Bithorax complex – includes genes that influence

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