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DNA mRNA Protein transcription translation DNA mRNA Protein transcription Chromosome translation Organization of DNA into Chromosomes allows for orderlyy p process of nuclear functions such as Molecular Level { Organization of DNA into Chromosomes allows for orderlyy p process of nuclear functions such as Molecular Level { DNA transcription DNA replication DNA repair etc etc. Organization of DNA into Chromosomes allows for orderlyy p process of nuclear functions such as Molecular Level { Cellular Level { DNA transcription DNA replication DNA repair etc etc. Organization of DNA into Chromosomes allows for orderlyy p process of nuclear functions such as Molecular Level Cellular Level { DNA transcription DNA replication DNA repair etc etc. { Nuclear vs. Cytoplasmic organization Chromosome duplication Chromosome separation Cell Division etc. Organization of DNA into Chromosomes allows for orderlyy p process of nuclear functions such as Molecular Level Cellular Level { DNA transcription DNA replication DNA repair etc etc. { Nuclear vs. Cytoplasmic organization Chromosome duplication Chromosome separation Cell Division etc. { Reproduction Evolution Polyploidization etc. Organizmal Level C t Cytogenetics ti = The study of chromosome number, structure, function, and behavior in relation to gene inheritance, organization and expression i Chromosome Chromo = colored in response to dye Some = body Chromosome off Eukaryotes Ch E k t have h been b the th ttraditional diti l subject for cytogenetic analysis because they are large enough to be examined with light microscope History of cytogenetics ~1600 Janssen & Janssen, father & son lay claim to the invention of the compound microscope Soon after cellular structure of plants and animals were recognized Significant improvements in glass quality & lens manufacturing lead to Recognition of separate organelles within cells History of cytogenetics ~1600 Janssen & Janssen, father & son lay claim to the invention of the compound microscope Soon after cellular structure of plants and animals were recognized Significant improvements in glass quality & lens manufacturing lead to Recognition of separate organelles within cells Cell theory: History of cytogenetics ~1600 Janssen & Janssen, father & son lay claim to the invention of the compound microscope Soon after cellular structure of plants and animals were recognized Significant improvements in glass quality & lens manufacturing lead to Recognition of separate organelles within cells Cell theory: Cells and their nuclei were the basic units of structure and function in living organisms History of cytogenetics ~1600 Janssen & Janssen, father & son lay claim to the invention of the compound microscope Soon after cellular structure of plants and animals were recognized Significant improvements in glass quality & lens manufacturing lead to Recognition of separate organelles within cells Cell theory: Lineage theory: Cells and their nuclei were the basic units of structure and function in living organisms History of cytogenetics ~1600 Janssen & Janssen, father & son lay claim to the invention of the compound microscope Soon after cellular structure of plants and animals were recognized Significant improvements in glass quality & lens manufacturing lead to Recognition of separate organelles within cells Cell theory: Lineage theory: Cells and their nuclei were the basic units of structure and function in living organisms Cells are derived from preexisting i ti cells ll (i.e. (i all ll cells ll trace back to one original cell) End of 19th century Mitotic and meiotic cell division & sexual reproduction had been described Chromosomes had also been observed consistency of appearance suggested t d an important i t t basic b i function f ti End of 19th century Mitotic and meiotic cell division & sexual reproduction had been described Chromosomes had also been observed consistency of appearance suggested t d an important i t t basic b i function f ti Early 1900: Age of Genetics Mandel’s Laws are re-discovered Genes are the basic unit of inheritance e es are a e different d e e forms o s of o thee same sa e gene ge e that a segregate seg ega e during du g • Alleles gamete formation (Law of Segregation) • Alleles of different genes segregate independently (Law of independent assortment) End of 19th century Mitotic and meiotic cell division & sexual reproduction had been described Chromosomes had also been observed consistency of appearance suggested t d an important i t t basic b i function f ti Early 1900: Age of Genetics Mandel’s Laws are re-discovered Genes are the basic unit of inheritance e es are a e different d e e forms o s of o thee same sa e gene ge e that a segregate seg ega e during du g • Alleles gamete formation (Law of Segregation) • Alleles of different genes segregate independently (Law of independent assortment) Chromosome theory of heredity: Heredity characters are carried & passed on to generations in discrete units (Correlation between Mendelian inheritance and chromosome behavior) 1920s and 1930s Natural or irradiation induced alterations in chromosome number and structure were observed. This lead to parallel studies of genetics and cytogenetics. Gene expression was observed (Lampbrush chromosomes) 1920s and 1930s Natural or irradiation induced alterations in chromosome number and structure were observed. This lead to parallel studies of genetics and cytogenetics. Gene expression was observed (Lampbrush chromosomes) Recent history (Age of Molecular Cytogenetics) Gene localization (in situ) Details of chromosome structure Studies of genomes (FISH and GISH) Role of various chromosome regions is realized Artificial chromosomes are made Single chromosomes are purified etc. Future ? Tools of Cytogenetics Light microscope manipulating i l ti the th path th off light li ht thru th optics ti E i Eyepiece Tube Revolving nosepiece Objective Lenses Specimen Stage Iris control Condenser lever Condenser centering Focus control Condenser Filters Auxiliary lens Iris diaphragm Illumination Tools of Cytogenetics Light microscope manipulating i l ti the th path th off light li ht thru th optics ti Important factors •optics •wavelength of light •liquid q immersion •phase contrast •fluorescence •computer enhancement Transmitting electron, Scanning electron and Scanning tunneling microscopy have all increased the power of observation Glossary of terms Cytogenetics = The study of chromosome number, structure, function and behavior in relations to gene inheritance, organization and expression Chromosome= A structure composed of DNA and proteins Chromosome that bears part of the genetic information of the cell Mitosis= A process of cell division in Eukaryotic cells by which two daughter cells are formed Meiosis= A two stage type of cell division in sexually reproducing organisms that results in gametes with half the chromosome number of the original cell The Somatic Cell Cycle Maternal chromosome Diploid Zygote MITOSIS Paternal Diploid Zygote chromosome MITOSIS Maternal chromosome Diploid organism Paternal chromosome Diploid organism The Somatic Cell Cycle Stages of the cell cycle: M Mitosis= period of cell division Interpphase G1 Gap1=period period during cellular interphase from the end of one telophase to the beginning of DNA replication S Synthesis=period of pre-mitotic interphase when DNA is replicated G2 Gap2=period during interphase after completion of DNA replication and before beginning of prophase G1 and G2 are called gaps in the cell cycle when no DNA synthesis occurs Cytological observations of the cell cycle are divided into two parts, interphase and mitosis The Somatic Cell Cycle Mitosis G2 Phase Cell division Interphase S Phase G0 Phase G1 Phase The Mitotic cell cycle is essential to cell division and growth of an organism The Mitotic cell cycle is essential to cell division and growth of an organism Gene Expression and Cell Division conflict: The Mitotic cell cycle is essential to cell division and growth of an organism Gene Expression and Cell Division conflict: Gene expression requires that chromosomal DNA bbe uncoiled il d tto allow ll access to t enzymes such as RNA polymerase The Mitotic cell cycle is essential to cell division and growth of an organism Gene Expression and Cell Division conflict: Gene expression requires that chromosomal DNA bbe uncoiled il d tto allow ll access to t enzymes such as RNA polymerase Cell division requires that chromosomes be tightly coiled to allow orderly migration of chromosomes to daughter cells The Mitotic cell cycle is essential to cell division and growth of an organism Gene Expression and Cell Division conflict: Gene expression requires that chromosomal DNA bbe uncoiled il d tto allow ll access to t enzymes such as RNA polymerase Cell division requires that chromosomes be tightly coiled to allow orderly migration of chromosomes to daughter cells Gene Expression and Cell Division are separated into different stages The Somatic Cell Cycle Mitosis G2 Phase Cell division Interphase S Phase G0 Phase G1 Phase Interphase G1 1. Period of gene expression 2. Daughter cells retain the diploid set of chromosomes and DNA content is 2c 3. More variable in length than S, G2 or M 4. Some event duringg G1 is the focus of regulation of cell reproduction in tissues 5. Differentiated cells that cease to reproduce usually contain G1 amount of DNA (2c) whether cessation is reversible or irreversible (G0) Interphase G1 6 In cells that continue to reproduce, 6. reproduce the reproductive rate is governed by the average length of time that cells are retained in the G1 7. Measurement of DNA content in dormant plant embryos indicate cells are arrested in G1 8. G1 may be absent in rapidly proliferating cells of higher organisms, particularly during embryogenesis 9. Once cells progress from G1 to S, they are committed to proceed through mitosis Interphase S 1. Period of DNA synthesis (DNA content goes from 2c to 4c) 2 Autoradiography shows that DNA synthesis 2. is confined to a relatively short period 3. DNA replication is initiated by factors in th cytoplasm the t l a) when two or more nuclei share the same cytoplasm, y p theyy are nearly y always y synchronized Interphase S 4 DNA replication 4. li i iis initiated i i i d by b factors f in i the h cytoplasm b) Gurdon (1973) observed that DNA synthesis was initiated when nuclei from various tissue of Xenopus were implanted into an unfertilized egg c) Nuclei from adult liver, brain, and blood cells ll injected i j t d into i t mature t eggs off Xenopus initiated DNA synthesis within 90 minutes of injection d) Inhibition of protein synthesis in G1 will inhibit or delay on set of the S phase Interphase G2 1 The nucleus contains two diploid sets of 1. chromatids (DNA content is 4c) 2. Period required for cells to synthesize elements l t necessary for f chromosome h condensation and the construction and operation of the mitotic apparatus 3. Protein synthesis is necessary for cells to complete most of the G2 period, but protein synthesis required for mitosis is completed prior to prophase 4. G2 lasts until mitosis begins Interphase G2 5 The fusion of a mitotic HeLa cell with an 5. interphase cell results in condensation of interphase chromosomes (Rao and Johnson, 1970)) a) Chromosomes do not have to be replicated to respond to the condensation signal b) The condensation factor is effective across phylogenetic lines (Bull sperm, chicken erythrocytes, and mosquito were condensed by the HeLa factor) Life cycle of a sexually reproducing organism correlated with the amount of DNA per cell Fertilization Mitotic divisions Am mount of D DNA/cell C values S A 4 S A Meiotic divisions S A1 3 Z C C A2 2 G G 1 0 Sequence of stages G Gamete, G= Gamete Z Z=Zygote Zygote, S S=Period Period of DNA synthesis synthesis, A=Mitotic Anaphase, C=Somatic Cells, A1=First meiotic anaphase, A2= Second meiotic anaphase Mitosis A mechanism by which replicated chromosomes are evenly distributed to two daughter cells. Each of the daughter cells will have the same number and kind of chromosomes as the parent. Stages of mitosis: Interphase p Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis Stages of Mitosis Interphase: Chromosomes are fine diffuse strands and are difficult to see with light microscopy Chromosomes are duplicated The nuclear envelope is intact Interphase Stages of Mitosis Interphase: Chromosomes are fine diffuse strands and are difficult to see with light microscopy Chromosomes are duplicated The nuclear envelope is intact Prophase Chromosomes condense into distinct structures Chromosomes become visible with light microscopy Prophase Stages of Mitosis Interphase: Chromosomes are fine diffuse strands and are difficult to see with light microscopy Chromosomes are duplicated The nuclear envelope is intact Prophase Chromosomes condense into distinct structures Chromosomes become visible with light microscopy Prometaphase Further chromosome condensation Nuclear envelope disintegrates Chromosomes become associated with spindle i dl apparatus Sister chromatids remain attached at the centromere, but begin to separate at other regions Interphase Prophase Prometaphase Prometaphase Stages of Mitosis M Metaphase h Sister chromatid pairs are aligned near the spindle with centromeres still associated The centromeres orient toward opposite pools and are lined up on the metaphase plate Metaphase Interphase Prophase Prometaphase P Prometaphase t h Metaphase Stages of Mitosis M Metaphase h Sister chromatid pairs are aligned near the spindle with centromeres still associated The centromeres orient toward opposite pools and are lined up on the metaphase plate Anaphase p Sister chromatid pairs separate with one member of each pair moving toward the poles Anaphase Anaphase Stages of Mitosis M Metaphase h Sister chromatid pairs are aligned near the spindle with centromeres still associated The centromeres orient toward opposite pools and are lined up on the metaphase plate Anaphase p Sister chromatid pairs separate with one member of each pair moving toward the poles Telophase Chromatids reach opposite poles and poleward movement ceases New nuclear envelope is formed around each diploid chromosome set Chromosomes begin to decondense Anaphase Anaphase Telophase Telophase Stages of Mitosis Cytokinesis During i mitosis i i doubling d bli off all ll the h cytoplasmic l i organelles also occurs, they are distributed to daughter cells during this stage Central ring of myosin and actin fibers contract to separate the daughter cells In plants the cell plate is laid down in preparation for the rigid cell wall C t ki i Cytokinesis Anaphase Anaphase Telophase Cytokinesis Cytokinesis Mitotic Index = # of mitotic cells Total # of cells Mitotic cells = cells in stages from prophase to telophase Control of Mitotic Cell Di i i Division G2 Phase signal i l for f G2 to t mitosis transition S Phase M Phase G1 Phase start signal Molecular clock Control of Mitotic Cell Di i i Division a)) The onset of mitosis is accompanied p by y the presence of an active maturation (or mitosis) promoting factor (MPF) Control of Mitotic Cell Di i i Division The onset of mitosis is accompanied p by y the presence of an active maturation (or mitosis) promoting factor (MPF) MPF purified from frog eggs consists of two protein subunits (Lohka et al. 1988). These were recognized as the 34 kD Protein Kinase (P34cdc2) and 45 kD Btype cyclin. Active MPF triggers the onset of mitosis, immediately afterward following events occur: a)) Cyclin y activityy is degraded g b) The nuclear membrane begins to break down c)) Chromosome condensation begins g d) The spindle apparatus is organized Phosphates block active site Inactive P P Dephosphorylation P Phosphhorylation G2 S active site M G1 Breakdown of Cyclin B Cyclin B Buildup of Cyclin B Inactive P34 cdc2 (Protein kinase) = MPF or maturation-promoting factor or mitosis promoting factor Glossary of terms The Somatic Cell Cycle= Events that occur from one cell division to the next 2C= DNA content of nucleus in the somatic cells of an organism Chromatid= A single chromosomal strand; a metaphase chromosome is composed of two “sister” chromatids Centromere=A region of chromosome from which kinetichore microtubules radiate during mitosis or meiosis Kinetochore= A specialized region on the centromere that links each sister chromatid to the mitotic spindle Heterochromatin= non-transcribed non transcribed eukaryotic chromatin that is so highly compacted that it is visible with a light microscope during interphase Euchromatin The more open, Euchromatin= open unraveled form of eukaryotic chromatin, which is available for transcription