CHAPTER 20 ORGANELLE DNA The 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 chromosomes o mtDNA is abundant o mtDNA in animals tends to evolve more rapidly than nuclear DNA o mtDNA is typically inherited from only one parent so its genes are not reshuffled every generation by recombination Chloroplast DNA cpDNA DNA contained by chloroplasts The Biology of Mitochondria and Chloroplasts Mitochondrion and Chloroplast Structure The Genetics of Organelle Encoded Traits the occurrence of two distinct varieties of DNA within the Uniparental inheritance Heteroplasmy Replicative segregation cytoplasm of a single cell organelles segregate randomly into the two progeny cells Homoplasmy when a heteroplasmic cell divides and the when a cell has just mutant or just wild type sequences The Endosymbiotic Theory Endosymbiotic theory bacteria that became internal inhabitants of early eukaryotic cells Mitochondria and chloroplasts are membrane bounded organelles of mitochondria and chloroplasts were once free living eukaryotic cells that generally possess their own DNA Mitochondrial 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 organisms The 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 mtDNA o D loop and promoters for both the H and the L strands a region of the H strand that contains the origin of replication Yeast mtDNA Flowering plant mtDNA Nonuniversal Codons in mtDNA Exceptions to the universal code exist in mitochondrial DNA These exceptions differ among organisms The 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 characteristics The Evolution of mtDNA All mtDNA appears to have evolved from a common eubacterial ancestor but the 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 organization Model Genetic Organism The Yeast Saccharomyces cerevisiae Advantages of yeast as a model genetic organism o It is a eukaryotic organism o It is unicellular o Require little space o Large numbers can be grown easily and inexpensively o Exists in both diploid and haploid forms o 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 divisions o Tetrad o Tetrad analysis the genetic analysis of a tetrad o Yeast cells possess many of the genes found in humans and other the four cells produced by a single meiotic division complex multicellular eukaryotes Life cycle of yeast Genetic techniques with yeast Chloroplast DNA The 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 repeat The Replication Transcription and Translation of cpDNA Many aspects of the transcription and translation of cpDNA are similar to those of eubacteria The 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 structure Genome Comparisons The Intergenomic Exchange of Genetic Information Mitochondrial DNA and Aging in Humans CHAPTER 21 ADVANCED TOPICS IN GENETICS Developmental Genetics Immunogenetics and Cancer Genetics Flies with Extra Eyes Developmental Genetics Totipotent Determination having the potential to develop into any type of cell the process by which a cell becomes committed Cloning 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 development o Development must require the selective expression of genes The Genetics of Pattern Formation in Drosophila The development of the fruit fly Egg polarity genes play a crucial role in establishing the two main o Egg polarity genes axes of development in fruit flies developmental fate of the surrounding region o Morphogen a protein whose concentration gradient affects the Determination of the dorsal ventral axis Determination of the anterior posterior axis Segmentation genes o Segmentation genes individual segments o Three groups control the differentiation of the embryo into Homeotic genes Gap genes define large sections of the embryo Mutations in these genes eliminate groups of adjacent segments Pair rule genes affect alternate segments Segment polarity genes define regional sections of the embryo and 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 o Homeotic genes determine the identity of individual segments Products activate other genes that encode these segment specific characteristics o Homeobox Mutations cause body parts to occur in the wrong segments contained in each homeotic gene consist of 180 nucleotides encode 60 amino acids that serve as a DNA binding domain o Two major clusters Antennapedia complex fly s head and anterior thoracic segments affects the development of the adult Comprises five genes Bithorax complex posterior thoracic and abdominal segments includes genes that influence the adult fly s Comprises three genes o Homeotic complex the Antennapedia and bithorax genes All are located on the same chromosome Contains many sequences that regulate the