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Chapter 9 Extranuclear Inheritance Lecture Presentation by Dr. Cindy Malone, California State University Northridge © 2015 Pearson Education, Inc. Chapter 9: Introduction – Inheritance Observations revealed inheritance patterns fail to reflect Mendelian principles Indicate apparent extranuclear influence on phenotype Discovery of DNA in mitochondria and chloroplasts; extranuclear inheritance is now recognized as important aspect of genetics © 2015 Pearson Education, Inc. © 2015 Pearson Education, Inc. Chapter 9: Extranuclear Inheritance Extranuclear inheritance – Transmission of genetic information to offspring through cytoplasm not nucleus – Usually from one parent Varieties in extranuclear inheritance – Organelle heredity – Infectious heredity – Maternal effect © 2015 Pearson Education, Inc. Chapter 9: Organelle Heredity Organelle heredity – One variety of extranuclear inheritance – DNA contained in mitochondria or chloroplasts determines certain phenotypic characteristics of offspring © 2015 Pearson Education, Inc. Chapter 9: Infectious Heredity Infectious heredity – Variation of extranuclear inheritance – Results from symbiotic or parasitic association with microorganism – Inherited phenotype affected by microbe in host’s cytoplasm © 2015 Pearson Education, Inc. Chapter 9: Maternal Effect Maternal effect on phenotype – Variation of extranuclear inheritance – Nuclear gene products are stored in egg, then transmitted through ooplasm to offspring – Gene products in ovule distributed to embryo cells – influence phenotype © 2015 Pearson Education, Inc. 9.1 Organelle Heredity Involves DNA in Chloroplasts and Mitochondria © 2015 Pearson Education, Inc. Section 9.1: Organelle Heredity Organelle heredity – Involves DNA in chloroplast or mitochondria – Inheritance of chloroplast or mitochondrial traits often determined by phenotype of ovule source (Figure 9-1) © 2015 Pearson Education, Inc. Section 9.1: Chloroplast Mutation Mirabilis jalapa (four o’clock plant) – Plant has white, green, and variegated leaves – Mutation in DNA housed in chloroplast – Genetic defect eliminated green chlorophyll (lightabsorbing pigment within chloroplasts) (Figure 9-1) © 2015 Pearson Education, Inc. © 2015 Pearson Education, Inc. Figure 9-1 Section 9.2: DNA in Chloroplasts and Mitochondria DNA in mitochondria and chloroplasts is unlike DNA seen in nucleus of eukaryotic cells that house these organelles (Figures 9-6 and 9-7) © 2015 Pearson Education, Inc. Section 9.2: Endosymbiotic Theory Endosymbiotic theory (Lynn Margulis et al.) – Mitochondria and chloroplasts (organelles) arose independently 2 billion years ago from freeliving bacteria – Organelles possessed attributes of aerobic respiration and photosynthesis, respectively © 2015 Pearson Education, Inc. Section 9.2: Endosymbiotic Theory Main points of endosymbiotic theory – Bacteria were engulfed by larger eukaryotic cells – Beneficial symbiotic relationship developed – Bacteria lost ability to function autonomously – Eukaryotic cells gained oxidative respiration and photosynthesis © 2015 Pearson Education, Inc. Section 9.2: mtDNA and cpDNA mtDNA: Mitochondrial DNA – Exists in eukaryotes as double-stranded circular DNA – Smaller than DNA in chloroplasts cpDNA: Chloroplast DNA – Genes encode products involved in photosynthesis and translation © 2015 Pearson Education, Inc. Section 9.2: Ribosomal Variation Cytoplasm – Ribosomes are uniformly 80S Mitochondria – Ribosomes vary from 55S to 80S Chloroplasts – Genes coding for rRNA (16S and 23S) © 2015 Pearson Education, Inc. Section 9.2: Mitochondrial Gene Products Majority of proteins for mitochondrial function are encoded by nuclear genes – DNA and RNA polymerase – Initiation and elongation factors – Ribosomal Proteins – Aminoacyl tRNA synthetases (Figure 9-8) © 2015 Pearson Education, Inc. © 2015 Pearson Education, Inc. Figure 9-8 9.3 Mutations in Mitochondrial DNA Cause Human Disorders © 2015 Pearson Education, Inc. Section 9.3: mtDNA in Humans Human mtDNA – Contains 16,569 base pairs – Coding for 13 proteins required for aerobic cellular respiration – Disruption of mitochondrial genes via mutation has severe impacts on organism © 2015 Pearson Education, Inc. Section 9.3: mtDNA Mutations mtDNA susceptible to mutations – No structural protection from histones – DNA repair mechanism limited – High concentrations of ROS (reactive oxygen species) generated by cell respiration ROS is toxic—damages organelle contents (proteins, lipids, mtDNA) © 2015 Pearson Education, Inc. Section 9.3: mtDNA Human Disorder Criteria for human disorder to be attributed to mtDNA – Inheritance must exhibit maternal inheritance pattern – Disorder must reflect deficiency in bioenergetic function of organelle – Must have mutation in one or more mitochondrial gene © 2015 Pearson Education, Inc. Section 9.3: mtDNA Disorders Three disorders arising from mtDNA – MERRF (myoclonic epilepsy and ragged-red fiber disease) – LHON (Leber’s hereditary optic neuropathy) – KSS (Kearns–Sayre syndrome) © 2015 Pearson Education, Inc. Section 9.3: mtDNA Disorder: MERRF Myoclonic epilepsy and ragged-red fiber disease – Pattern of inheritance consistent with maternal transmission – Lack of muscular coordination – “Ragged-red” skeletal muscle fibers (Figure 9-9) © 2015 Pearson Education, Inc. Section 9.3: Mitochondria, Health, and Aging Mitochondrial dysfunction implicated in most human diseases – Anemia – Blindness – Type II diabetes – Autism – Infertility – Neurodegenerative diseases: Parkinson and Alzheimer © 2015 Pearson Education, Inc. Section 9.3: Prevention of mtDNA Disorders 1 in 5000 humans have mtDNA-based disease or are at risk for developing one – Can be detected by genetic testing – New therapies can prevent transmission of mtDNA mutations to offspring – Figure 9-10: Mitochondrial swapping in oocytes © 2015 Pearson Education, Inc. © 2015 Pearson Education, Inc. Figure 9-10 Section 9.4: Maternal Effect Maternal effect (maternal influence) – Offspring’s phenotype is under control of nuclear gene products present in egg – Nuclear genes of female gamete transcribed; genetic products accumulate in egg’s cytoplasm – Products distributed among newly formed cells, influencing patterns/traits established early in development © 2015 Pearson Education, Inc. Section 9.4: Maternal Effect (Snails) Lymnaea peregra (snail) – Shell coiling in Lymnaea peregra – Example of maternal effect on permanent rather than transitory phenotype – Coiling pattern of progeny snails determined by genotype of parent producing egg, regardless of phenotype of parent (Figure 9-11) © 2015 Pearson Education, Inc. © 2015 Pearson Education, Inc. Figure 9-11