cytogen-midterms (1).pdf

CYTOGENETICS 01 MIDTERMS – INTRODUCTION TO CYTOGENETICS Walther Flemming Cytologist...

CYTOGENETICS 01 MIDTERMS – INTRODUCTION TO CYTOGENETICS Walther Flemming Cytologist CYTOGENETICS Anatomy Professor Combination of methods and findings in Cytology and Published in 1882 → First Genetics Illustrations of human Investigation of heredity at the cellular level chromosomes Identified chromatin CYTOLOGY First used the term MITOSIS Study of cells as fundamental units of living things GENETICS Study of biologically inherited traits August Weismann HISTORY OF CLINICAL CYTOGENITICS 1883 → Theory of continuity of Early Genetics the germ plasm Carolus Linnaeus → Classification System Germ Plasm → heritable information is transmitted only by germ cells Heinrich Wilhelm Gottfried von Waldeyer-Hartz 1888 → chromosome Charles Darwin → EVOLUTION THEORY by Natural Selection Hugo De Vries, Erich von Tschermak-Seysenegg, Carl Correns 1901 → rediscovered Mendel’s law Walter Sutton Developed → chromosome Gregor Johann Mendel theory of inheritance Discovered fundamental laws of He stated that the Mendelian heredity laws of inheritance could be 1865 → Published his applied to chromosomes investigations info inheritance of Combined the disciplines of pea plants cytology and genetics → Father of Genetics Cytogenetics Theodor Boveri Eduard Strasburger Chromosomes are involve with 1879 → led to the theory that cell inheritance nucleus is the bearer of the physical basis heredity Flores, Keziah Hymn S.  CYTOGENETICS Boveri-Sutton Chromosome Theory Terminologies: Identified chromosomes as the genetic material responsible for Mendelian inheritance CHROMOSOMES Special structure that is found in cells The Chromosome Theory of Inheritance Made up of an organized section/strand of DNA that contains many genes Every human body cell has 23 pairs → 46 chromosomes DNA Deoxyribonucleic acid Double helix shaped molecule Contains all the genetic materials → determines the information available for building and maintaining an organism GENE Special segment of DNA that is found on a chromosome Codes for a particular protein that determines a particular trait/feature/characteristic The Chromosomal Theory of Inheritance was consistent with Mendel’s laws and was supported by the following observations: During meiosis, homologous chromosome pairs migrate as discrete structures that are independent of other chromosome pairs. The sorting of chromosomes from each homologous pair into pre-gametes appears to be random. Each parent synthesizes gametes that contain only half of their chromosomal complement. Even though male and female gametes (sperm and egg) differ in size and morphology, they have the same number of chromosomes, suggesting equal genetic contributions from each parent. The gametic chromosomes combine during fertilization to produce offspring with the same chromosome number as their parents. Clarence Erwin McClung 1902 → suggested that the sex determination was related to some special chromosomes ALLELES Different forms of a gene, which produce variations in a genetically inherited trait o Dominant allele o Recessive allele Grigorii Andreevich Levitsky Karyotype → ordered LOCI/LOCUS arrangement of chromosomes Specific location of a gene for some trait on a chromosome Alleles are arranged in loci on chromosomes Flores, Keziah Hymn S.  CYTOGENETICS HOMOLOGOUS CHROMOSOME CARRIER A pair of chromosomes that is similar in length, gene Individual who is heterozygous for a trait that only shows up position, centromere location. in the phenotype of those who are homozygous recessive Genes may contain different allele TRAIT Specific characteristic of an organism It can be determined by genes or the environment or more commonly by interactions between them HEREDITY Inheritance or biological inheritance Characteristics that are transmitted from parents to their offspring PHENOTYPE Observable expression of that genetic information as cellular, morphological, clinical, or biochemical trait GENOTYPE Genetic makeup of an organism Determines phenotype DOMINANT Alleles that dominates over others in determining phenotype HOMOZYGOUS GENOTYPE When both alleles at a particular gene locus are the same HETEROZYGOUS GENOTYPE When the two alleles at a particular gene locus are different RECESSIVE Allele whose phenotypic expression is “hidden” when a dominant allele is present Flores, Keziah Hymn S.  CYTOGENETICS 02 MIDTERMS – CELL BIOLOGY CYTOSKELETON (Under the Cytosol) Supports the cell CELL Holds the nucleus and other organelles in place Basic unit of life or of all living things Responsible for changes in cell shape & movement of cell organelles 2 Types of Cell: Consists of three groups of proteins: Eukaryote – HAS nucleus 1. Microtubules Prokaryote – no nucleus 2. Actin filaments/Microfilament 3. Intermediate filaments 1. Microtubules (Under the Cytoskeleton) Hollow tubes Composed of protein units → tubulin Internal scaffolding Provides support and structure to the cytoplasm of the cell Form essential components of certain cell organelles, such as centrioles, spindle fibers, cilia, and flagella Centrioles (Under the Microtubules) Small, cylindrical organelle Length → 0.3-0.5 μm Diameter → 0.15 μm Involved in the development of spindle fibers in cell division 9 set of triple microtubules 3 Parts of Cell: Centrosome – 2 centrioles Internal structures Membrane structures Spindle Fibers (Under the Microtubules) External structures Involved in moving and segregating the chromosomes during nuclear division INTERNAL STRUCTURES Protoplasm Everything included in the cell membrane (lahat ng nasa loob ng cell membrane) proto means first, plasm means substance Divided into two: o Cytoplasm – everything included in the cell EXCEPT from nucleus ▪ Cytosol – fluid portion of the cytoplasm; contains cytoskeleton & 2. Actin filaments (or microfilaments, under the Cytoskeleton) cytoplasmic inclusions Small fibrils ▪ Organelles – an endomembrane Bundles, sheets, or networks in the cytoplasm system which compose of ER, Provide structure to the cytoplasm ribosomes, golgi apparatus and Mechanical support for microvilli vesicles. Mitochondria (energy Support the plasma membrane production), and detoxification Define the shape of the cell o Nucleoplasm – everything inside the nucleus Also for the movement because it can control the cells to move CYTOPLASM Consists of all the contents outside of the nucleus and 3. Intermediate filaments enclosed within the cell membrane of a cell Protein fibers Clear; gel-like appearance Provide mechanical strength to cells CYTOSOL (Under the Cytoplasm) Fluid portion of cytoplasm → colloid Contains (1) Cytoskeleton and (2) Cytoplasmic inclusions Difference of Cytosol and Cytoplasm Flores, Keziah Hymn S.  CYTOGENETICS ORGANELLES (Under the Cytoplasm) Endomembrane System Nucleus contains: o Endoplasmic reticulum Chromosomes o Ribosome Chromatin - histones o Golgi apparatus Nucleoplasm – semi-fluid medium of the nucleus o Vesicle Nuclear envelope – membrane of the nucleus; Energy Production phospholipid membrane which separates the nucleoplasm Detoxification from cytoplasm Nucleolus – dark-staining spherical bodies in the nucleus Organelles for Endoplasmic Reticulum: site where the rRNA joins proteins to form ribosomes Consists of broad, flattened, interconnecting sacs and Nuclear pore – permits passage of proteins into nucleus tubules and ribosomal subunits System of channels → passageway in the cell Transporting, synthesizing, and storing materials CELL MEMBRANE 2 Kinds: Or plasma membrane Rough endoplasmic reticulum (RER) – has ribosome Separates the inner contents of a cell from its exterior Smooth endoplasmic reticulum (SER) environment Selectively permeable Rough Endoplasmic Reticulum (RER) Provides protective barrier & regulates transport materials Membranes that create a network of channels throughout in and out of the cell the cytoplasm Attachment of ribosomes to the membrane gives a rough Contains: appearance 45-50% Lipids Synthesis of protein 45-50% Proteins 4-8% Carbohydrates Ribosome Protein synthesizers Found within the cytosol of the cytoplasm and attached to internal membranes Smooth Endoplasmic Reticulum (SER) Closed tubular network without ribosomes FUNCTIONS: Synthesis of carbohydrates, lipids, and steroid hormones Detoxification of medications and poisons/foreign substances Storage of calcium ions – sarcoplasmic reticulum – muscle cell Golgi Apparatus Packaging machine Packaging and distribution of materials to different part of the cell EXTERNAL STRUCTURES Secretory Vesicles Cilia Tiny packages Cylindrical shaped projections Contains materials that can be secreted For movement Hair Example of secretory vesicles: Length → 10 μm Lysosomes Diameter → 0.2 μm Membrane-bound vesicles containing digestive enzymes- from Golgi Flagella Longer than cilia Destroy cells or foreign matter that the cell has engulfed by Length → 45 μm phagocytosis Can be seen in sperm cells Organelles for Energy Production and Detoxification: Microvilli Mitochondria Cylindrical shaped extensions For energy production NOT for movement → for Absorption Energy generators of the cell Found on the cells of intestine and kidney “Powerhouse of the cell” – cellular metabolism Contains ATP synthase – produces ATP or energy 03 MIDTERMS – NUCLEIC ACIDS Peroxisomes For Detoxification Biochemistry Smaller than lysosomes Bio means life and chemistry means interactions of elements or Contain enzymes molecules that sustains our life. o Catalase → H2O2 Cells that are active in detoxification → Liver & Kidney cells Macromolecules 1. Carbohydrates (sugars) – CH2O (carbons and hydrates) Nucleus a. Monosaccharides – one sugar unit (Glucose, Largest; Central Organelle Galactose, and Fructose) Contains the cell’s DNA b. Disaccharide – two sugar units (Maltose, Control center Lactose, Sucrose) Flores, Keziah Hymn S.  CYTOGENETICS c. Polysaccharide – Glycogen (storage form of 2. Nitrogen-Containing Heterocyclic Bases glucose), Starch (storage form of glucose in plant 5 nitrogen containing heterocyclic bases are nucleotide cells) components 2. Lipids (Fats, triglycerides, cholesterol, phospholipids) 3 Pyrimidine – a monocyclic base with six-membered ring 3. Proteins – Polypeptide 2 Purine – a bicyclic base with fused five- and six- a. Monomer unit: Amino acids membered rings. b. About enzymes, vitamins (organic), and minerals (inorganic) 4. Nucleic acids – Polymer a. Monomer unit: Nucleotide i. Sugar unit ii. Nitrogenous base iii. Phosphate group b. DNA and RNA History of Nucleic Acids Freidrich Miescher (1844-1895) > Pyrimidine 3 Monocyclic CUT – Cytosine, Uracine (for RNA), and Thymine (for DNA) Swiss physiologist Discovered Nucleic Acids in 1869 while studying the nuclei of WBC NUCLEIC ACID – found in cell nuclei and are acidic Note: Although nucleic acids are found through out a cell, not just in the nucleus Nucleic Acid Polymer in which the monomer units are nucleotides Polynucleotides Made up of C, H, O, N, P > Purine o Carbon, hydrogen, oxygen, nitrogen, and 2 phosphate Bicyclic o Protein – CHON PAG – Adenine and Guanine o Carbohydrate - CHO Nucleotides: Building Blocks of Nucleic Acids Three-subunit molecule in which a pentose sugar is bonded to both a phosphate group and a nitrogen-containing heterocyclic base 3. Phosphate Derived from phosphoric acid (H3PO4) Phosphate residue is attached to pentose sugar DNA/RNA via the 5’C by a phosphodiester link Acidic, Nucleic acid All residues in the DNA/RNA carry a negative charge in physiologic pH. 1. Pentose Sugars Sugar unit of a nucleotide is either the pentose ribose or the pentose 2’-deoxyribose (walang OXYgen sa carbon 2) Flores, Keziah Hymn S.  CYTOGENETICS Nucleoside Formation Nucleoside → a two sub-unit molecule in which a pentose sugar is bonded to a nitrogen containing heterocyclic base. RULE: Base is always attached to Carbon 1 of the sugar Condensation reaction → a molecule of water is formed as the 2 molecules bond together Inside the cell, we have the nucleus, and inside the nucleus there is chromosome. Chromosomes contains of DNA strands, which is the nucleic acid and there is what we call the segments in DNA which is the gene. Pyrimidine bases, suffix –idine is used (cytidine, thymidine, uridine) Primary Structure of Nucleic Acid Purine bases, the suffix –osine is used (adenosine, 1. Polynucleotide chains have sense or directionality (3’ unreacted guanosine) hydroxyl group and unreacted 5’ phosphate group) Prefix deoxy- indicates that sugar unit is deoxyribose (no 2. Polynucleotide have individuality (nucleotide base sequence) oxygen) basis for the different amino acids. Codons – essential for protein synthesis Nucleotide Formation Phosphate group is attached to the sugar at carbon 5 position via phosphoester linkage Water molecule is produced formation Base Pairing The size of the interior of the DNA double helix, limits the base pairs that can hydrogen bond to one another. Nucleic Acid Only pairs involving one small base (a pyrimidine, CT) and one large base (a purine, AG) correctly fit. A-T, G-C, A-C, G-T Apples in the Tree, Car in the Garage Types of Nucleic Acids and their Structure 1. Ribonucleic acid (RNA) 2. Deoxyribonucleic acid (DNA) Watson-Crick Model Ribonucleic Acid (RNA) Combination of two single strands Nucleotide polymer in which each of the monomers The Double Helix contains ribose (Carbon 2: OH), a phosphate group, and Sugar-phosphate backbone outside, bases inside one of the heterocyclic bases: Adenine, Cytosine, Bases form specific base pairs, held together by hydrogen Guanine, or Uracil. bonds Occurs in all parts of a cell Primary function is Synthesis of Proteins Deoxyribonucleic Acid (DNA) Nucleotide polymer in which each of the monomers contains deoxyribose (Carbon 2: H, meaning no Oxygen), a phosphate group, and one of the heterocyclic bases: Adenine, Cytosine, Guanine, or Thymine Found within the cell nucleus Primary function is the storage and transfer of genetic formation This information is used to control many functions of a living cell (Control Center: Nucleus, because of DNA) DNA is passed from existing cells to new cells during cell division. Flores, Keziah Hymn S.  CYTOGENETICS ANTIPARALLEL – Nature of two polynucleotide chains in > Small nuclear RNA (snRNA) DNA double helix means that there is a 5’ and a 3’ end at RNA that facilitates the conversion of heterogeneous both ends of double helix nuclear RNA to messenger RNA. o 5’ (5 prime) – 3’ (3 prime) or 3’-5’ COMPLEMENTARY BASES – Pairs of bases in a nucleic acid structure that can hydrogen bond to each other o A-T, G-C > Ribosomal RNA (rRNA) RNA that combines with specific proteins to form ribosomes, the physical sites for protein synthesis Predict the sequences of bases in the DNA strand complementary to the single DNA strand shown: 5’ A-A-T-G-C-A-G-C-T 3’ 3’ T-T-A-C-G-T-C-G-A 5’ 5’ G-T-A-A-C-T-C-G-A 3’ 3’ C-A-T-T-G-A-G-C-T 5’ > Transfer RNA (tRNA) RNA that delivers amino acids to the sites for protein Ribonucleic Acids synthesis. The sugar unit in the backbone of RNA is ribose Smallest RNA In RNA, Uracil instead of thymine, pairs with adenine. RNA is a single stranded molecule RNA molecules are smaller than DNA molecules Types of RNA Molecules 1. Heterogeneous nuclear RNA (hnRNA) 2. Messenger RNA (mRNA) 3. Small nuclear RNA (snRNA) 4. Ribosomal RNA (rRNA) 5. Transfer RNA (tRNA) > Heterogeneous nuclear RNA (hnRNA) RNA formed by DNA transcription Post-transcription processing converts the hnRNA to mRNA Predict the sequences of bases in the RNA strand complementary to the single RNA strand shown: 5’ A-A-T-G-C-A-G-C-T 3’ 3’ U-U-A-C-G-U-C-G-A 5’ 5’ G-T-A-A-C-T-C-G-A 3’ > Messenger RNA (mRNA) 3’ C-A-U-U-G-A-G-C-U 5’ RNA that carries instructions for protein synthesis (genetic information) to the sites for protein synthesis. Flores, Keziah Hymn S.  CYTOGENETICS 04 MIDTERMS – CENTRAL DOGMA 2 strands of the DNA from unwinding are called templates Explains the flow of genetic information from the DNA to RNA and to (parent DNA) make a functional product which is the protein. The DNA makes RNA, RNA primase → enzyme that synthesizes short RNA and RNA makes proteins. sequences (primers); serve as a starting point for DNA DNA replication synthesis Transcription o Polymerization process – process of reacting Translation monomer molecules together in a chemical reaction to form a polymer chain (pagpapadami ng monomer) Free nucleotides pair with their complementary base on template strands by means of hydrogen bonds. DNA polymerase III → catalyzes the formation of a new phosphodiester linkage between the nucleotide and growing strand; joins the newly attached nucleotides to Replication of DNA create one continuous strand in the 5’ to 3’ direction. Biochemical process by which DNA molecules produce Only one strand can grow continuously in the 5’ –to-3’ exact duplicates of themselves direction (leading strand) At the origins of replication, DNA helicase unwinds the The other strand is formed in short segment (OKAZAKI DNA double helix fragments) in the 3’-to-5’ direction (lagging strand) Breaking of hydrogen bonds between complementary Nicks → breaks and gaps in Okazaki fragments bases Segments are then joined together by DNA ligase Topoisomerase → untangle and reduce the tension of DNA strands Replication fork → unwinding point of DNA which is constantly changing/moving Leading strand – 5 to 3 Lagging strand – 3 to 5 Template – complementary of leading and lagging strand Enzymes in DNA replication DNA Helicase Topoisomerase RNA Primase DNA Polymerase SSB proteins - Single Strand DNA binding protein o DNA Pol I → Exonuclease activity; remove RNA o Keep the strands separated by holding them in primer & replaces w/ DNA place o DNA Pol II → Repair function (taga-ayos) o So that each strand can serve as a template for o DNA Pol III → Main enzyme that adds new DNA synthesis nucleotides in the 5’ to – 3’ direction DNA Ligase – joins the segments in lagging strands Other Requirements in DNA Replication Protein: SSB (Single stranded binding protein) Nucleic Acid: Primer – RNA (Free) Nucleotides Flores, Keziah Hymn S.  CYTOGENETICS Summary: The replication of DNA begins at a sequence of Post-Transcription (Formation of mRNA) nucleotides called the origin of replication. Helicase unwinds the Conversion of hnRNA to mRNA double-stranded DNA helix and single-strand binding proteins Genes contains 2 segments (SSB) react with the singe-stranded regions of the DNA and stabilize o EXONS → contains/codes for genetic it. DNA Polymerase III is the major enzyme involve in DNA information (DNA segments that help express a replication. DNA Polymerase III can only add a nucleotide to the 3’ genetic message) and of the pre-existing chain of nucleotides and it cannot initiate a o INTRONS → portion that do not convey genetic nucleotide chain. Therefore, an RNA Polymerase called a Primase, information (DNA segments that interrupt a constructs an RNA Primer, a sequence of about 10 nucleotides genetic message); should be removed complementary to the parent DNA. DNA Polymerase III can then add Deoxyribonucleotides to synthesize the new complementary strand of Genetic Code DNA. Because the two parent-strands of DNA are anti-parallel, they are oriented in opposite directions and must therefore be elongated by different mechanisms. The leading strand elongates toward the replication fork by adding nucleotides continuously to its growing 3’ end. In contrast, the lagging strand, which elongates away from the replication from the replication fork, is synthesized discontinuously as a series of short segments called Okazaki fragments. When the DNA Polymerase III reaches the RNA Primer on the lagging strand, it is replaced by DNA Polymerase I, which removes the RNA and replaces it with DNA. DNA ligase then attaches and forms phosphodiester bonds. The DNA is further unwound new primers are made and DNA Polymerase III jumps ahead to begin synthesizing another Okazaki fragment. For simplicity, DNA Polymerase III has been depicted as separate units, 1 acting on the leading strand and the other acting on the lagging strand. The current view of DNA Polymerase III is that the two sub-units function together with the DNA on the lagging strand, folding to allowed the dimeric DNA Polymerase molecule to replicate both strands of the parental DNA duplex simultaneously. Proteins other than DNA Polymerase III are not shown. Transcription In nucleus DNA TO RNA (double to single-stranded nucleic acid) RNA Molecules 1. Heterogeneous nuclear RNA (hnRNA) – pre mRNA; uncoded 2. Messenger RNA (mRNA) – coded RNA 3. Small nuclear RNA (snRNA) 4. Ribosomal RNA (rRNA) – ribosomes 5. Transfer RNA (tRNA) – delivers amino acids for protein synthesis; smallest Transcription (RNA Synthesis) Process by which DNA direct the synthesis of hnRNA/ mRNA molecules that carry information needed for protein synthesis. Post-transcription: Splicing Transcription (Formation of hnRNA) Process of removing intron from hnRNA molecule and A portion of DNA unwinds by RNA polymerase joining the remaining exons together to form a mRNA Free ribonucleotides aligns the strand exposed and form molecule new base pairs Involves snRNA which always complexed with snRNP U rather than T aligns with A in base pairing process (AT → Small Nuclear Ribonucleoprotein Particle → complex AU) formed from a snRNA molecule and several proteins RNA polymerase links the ribonucleotide to the growing Spliceosomes → large assembly of snRNA molecules and hnRNA molecule proteins involved in the conversion of hnRNA molecules to Ends when RNA polymerase encounters the stop signal mRNA molecules. RNA polymerase and hnRNA released DNA rewinds to reform the original double helix Alternative Splicing Template strand → DNA strand used for hnRNA/ mRNA Process by which several different proteins that are synthesis variations of a basic structural motif can be produced from Informational strand → non template stran d, gives the a single gene. base sequence present in the hnRNA except for U replacing T Flores, Keziah Hymn S.  CYTOGENETICS Anticodon 3 nucleotide sequence on a tRNA molecule that is complementary to a codon on a mRNA molecule. Transcriptome All of RNA molecules that can be generated from the Translation genetic material in a genome. Process by which mRNA codons are deciphered and a particular protein molecule is synthesized. Process by which the genetic message is decoded and used to make proteins. Every cell contains 20 or more different tRNAs, each designed to carry a specific amino acid (1st Step) Activation of tRNA 1. An amino acid interacts with an activator molecule to form a highly energetic complex 2. The complex reacts with tRNA to produce an activated tRNA molecule Activated tRNA → tRNA that has an amino acid covalently bonded to it at its 3’ end through an ester linkage (2nd Step) Initiation mRNA attaches to the surface of a small ribosomal subunit such that its first codon, which is always the initiating codon AUG- methionine, occupies the P site (peptidyl site) RNA Polymerase I – rRNA (in nucleolus) II – mRNA III – tRNA (3rd Step) Elongation Another tRNA with the second amino acid binds at the A Translation site. RNA to Protein The methionine transfers from P site to the A site. tRNA The ribosome shift to the next codon, making it’s a site Clover leaf shape available for the tRNA carrying the third amino acid. At the 3’ end, amino acid is attached Loop opposite the open end (anticodon loop), contains (4th Step) Termination anticodon The polypeptide chain continues to lengthen until a stop codon (UAA, UAG, UGA) appears on the mRNA. The new protein is cleaved from the last tRNA. Post-translational processing Post translational modification Gives the protein final form to be functional Flores, Keziah Hymn S.  CYTOGENETICS 05 MIDTERMS – CELL CYCLE & CELL DIVISION Mitosis or M Phase Mitosis begins after G2 and ends before G1. Cell Cycle Series of events that take place in a cell leading to its division and Stages of Mitosis (PMAT): duplication of its DNA to produce daughter cells. Prophase Cell cycle has two parts: Metaphase Cell growth & preparation → Interphase Anaphase Cell division Telophase o Mitosis → somatic cells o Meiosis → gametes (sex) cells 1. Prophase Cell begins the division process Interphase Nuclear membrane breaks apart This is where the cell prepares itself for cell division Chromosome condenses Occurs between divisions Nucleolus disappears Longest part of cycle Microtubules form 3 stages o G1 → GAP 1 o S → Synthesis o G2 → GAP 2 G1 or Gap 1 The cell just finished dividing Cell is recovering from mitosis Metabolic changes prepare the cell for division During the G1 phase of the cell cycle, protein and RNA synthesis resume after being interrupted during mitosis. This phase involves cell growth and maturation, allowing 2. Metaphase the cell to perform its physiological functions. G1 is 2nd phase of Mitosis characterized by the synthesis of RNA and proteins Chromosomes are pulled to center of cell necessary for cell growth and development, involving Line up along “metaphase plate” processes like transcription and translation as outlined in the central dogma of molecular biology. G1 phase is usually termed as the prior to the DNA synthesis phase or the S phase. S or Synthesis stage DNA replicates G2 or Gap 2 Preparation for mitosis Organelles are replicated More growth occurs 3. Anaphase Increased synthesis RNA & proteins 3rd phase of mitosis Centromeres divide Note: Each of the stage has a checkpoint. Their job is to check if there Precise alignment is critical to division is an error to the cells. If there is, some of the cells are to be repaired but some goes to G0 (G zero – cell cycle arrest), in which the cells are arrested. It will undergo apoptosis (cell death, can no longer be used). 4. Telophase Two events take place during telophase, the final stage of mitosis: o Formation of nuclei o Division of the cytoplasm (cytokinesis) Cell Division Why do cells divide? Formation of nuclei For growth, repair, and reproduction o Spindle fibers break down Cell Division VS. Nuclear Division o Membrane buds from the endoplasmic reticulum Cytokinesis → actual division of the cell into two new cells to form a new nuclear membrane Mitosis → division of the nucleus of the cell into two nuclei o Inside the new nucleus → chromosomes uncoil, Note: Sometimes cells go through mitosis without going lengthen, and form threads and clumps of through cytokinesis chromatin Megakaryocyte: A cell responsible for producing platelets. It undergoes endomitosis, a process where only the nucleus divides without the cell undergoing cytokinesis (no division of the cytoplasm or the cell itself). When a megakaryocyte matures, it ruptures, releasing fragments that become platelets. Flores, Keziah Hymn S.  CYTOGENETICS Cytokinesis Meiosis I o Cytoplasm, organelles and nuclear material are Prophase I evenly split Chromosomes condenses o 2 new cells are formed Homologous chromosomes pair (match up – synapsis) w/ o Cleavage furrow each other Each pair contains four sister chromatids – tetrad Meiosis 1. Leptotene A division of the nucleus that reduces chromosome number Thin threads by half (23) Replicated chromosomes condense Important in sexual reproduction Chromosome becomes visible Involves combining the genetic information of one parent Homologous chromosomes are unpair with that of the other parent to produce a genetically distinct Each chromosome begins to search its homologue individual Terminology Diploid – Two sets of chromosomes (2n), in humans 23 pairs or 46 total Haploid – One set of chromosomes (n) – gametes or sex cells, in humans 23 chromosomes Chromosome Pairing Homologous pair o Each chromosome in pair is identical to the other (carry genes for same trait) o only one pair differs – sex chromosomes X or Y Phases of Meiosis 2. Zygotene A diploid (2n) cell replicates its chromosomes Paired threads Two stages of meiosis Homologous chromosomes became closely associated o Meiosis I and Meiosis II (synapsis) to form pairs of chromosomes (bivalents) o Only 1 replication will occur consisting of four sister chromatids (tetrads) Synapsis Pairing of homologous chromosomes forming a tetrad Allows matching up of homologous pair prior to their segregation & possible chromosomal crossover between them Tetrad → 2 pairs of homologous chromosomes next to each other 3. Pachytene Synapsis was completed Crossing over between homologous chromosomes is Crossing Over possible Exchange of segments between each non-sister chromatid (tetrad) Chiasmata → points where non-sister chromatids had swapped sections Flores, Keziah Hymn S.  CYTOGENETICS 4. Diplotene Anaphase II Homologous chromosomes separate partially but are Centromeres split held together at cross-overs (chiasmata) Individual chromosomes are pulled to poles The chromatids of the chromosomes finally separate, becoming chromosomes in their own right, and are pulled to opposite poles Telophase II & Cytokinesis Four haploid (23) daughter cells result from one original diploid cell The chromosomes gather into nuclei, and the cells divide Products of meiosis: each of the four cells has a nucleus with a haploid number of chromosomes Mitosis Meiosis This type of division takes place This type of division takes place 5. Diakinesis in somatic cells. in gametic cells. Chromosomes condense further Two daughter cells are formed. Four daughter cells are formed. Tetrads are actually visible Number of chromosomes Number of chromosomes Chiasmata terminalize → clearly visible remains diploid in daughter becomes haploid in daughter cells. cells. Mitosis is necessary for Meiosis is necessary for growth and repair. sexual reproduction. Metaphase I Tetrads or homologous chromosomes move to center of cell Random Assortment of Homologous Orientation of paternal and maternal homologous at the Anaphase I metaphase plate is random. Different combination of Homologous chromosomes pulled to opposite poles chromosomes occurs, because of crossing over. Therefore, no 2 cells have exactly the same gene content. Fertilization By reducing the number of chromosomes from 2n to n, the stage is set for the union of two (23 and 23) genomes If the parents differ genetically, new combinations of genes can occur in their offspring Telophase I Daughter nuclei formed The process of asexual reproduction begins after a sperm fertilizes an egg. Meiosis II Daughter cells undergo a second division; much like mitosis NO ADDITIONAL REPLICATION OCCURS Prophase II Spindle fibers form again Similarities of Mitosis & Meiosis The chromosomes condense again, following a brief Both are forms of nuclear division interphase in which DNA does not replicate Both involve 1 replication only Both involve disappearance of the nucleus, and nucleolus, Metaphase II nuclear membrane Sister chromatids move to the center Both involve formation of spindle fibers Kinetochores (complex of protein in the centromere) the paired chromatids line up across the equator of each cell Flores, Keziah Hymn S.  CYTOGENETICS Difference Classification based on Centromere Location: Meiosis produces daughter cells that have ½ the number Metacentric of chromosomes as the parent. Go from 2n to 1n. Submetacentric Daughter cells produced by meiosis are not genetically Acrocentric identical to one another. Telocentric In meiosis cell division takes place twice but replication occurs only once. Metacentric Two arms are roughly equal in length Value of Variation Hard to distinguish which is the p arm and Variation – differences between members of a population q arm because the centromere is exactly in Meiosis results in random separation of chromosomes in the middle gametes Chromosomes: Causes diverse populations that over time can be stronger 1, 3, 16, 19, 20 for survival 06 MIDTERMS – CHROMOSOMES Submetacentric Chromosome Short and long arms of unequal length with chroma means color; some/soma means bodies the centromere more towards one end Threadlike structures Common; p arm and q arm can be easily Contains genes identified Colored bodies Chromosomes: are threadlike structures that are located inside our nucleus. 2, 4, 5, 6, 7, 8, 9, 10, 11, 12, 17, 18 It contains DNA and genes; colored bodies x Chromosome Structures Centromere → found in the middle; Acrocentric used during cell division as attachment p arm is hard to observe but still present point centromere is very near to one end and Telomere → both ends; used to have very small short arm maintain chromosomal integrity by acro means tip or top capping off the ends; telo means end Chromosomes: Short arm → p (petite) 13, 14, 15, 21, 22 Long arm → q (queue: tail) Y Telocentric Centromere is located at the terminal end of the chromosome Do not exist in humans Telo means end Mouses has telocentric Chromosomal Classification Stalk/Satellite (with Secondary Constriction) Autosome or sex chromosomes Centromere is also known as the Centromere location primary constriction Contains genes which code for Autosomal Chromosomes rRNA 22 pairs Responsible in nucleolus 1-22 chromosome formation Contain genes that are responsible for somatic SAT CHROMOSOMES → characteristics Chromosomes that contains satellite Sex Chromosomes 23rd pair Types of Chromosomes X and Y (XX female, XY male) Contains genes that encodes for our sexual characteristics that will identify the sex of an individual Flores, Keziah Hymn S.  CYTOGENETICS Chromosome Identification Group C Chromosome 6-12, X Medium size Submetacentric Group A Chromosomes: 1-3 Largest 1 and 3 are metacentric but 2 is submetacentric Chromosome 6 Medium submetacentric Largest among the Group C chromosomes 170 million base pairs Chromosome 7 Medium submetacentric 158 million base pairs X Chromosome Medium submetacentric 153 million base pairs Chromosome 8 Chromosome 1 Medium submetacentric Largest chromosome 146 million base pairs Metacentric 246 million base pairs Chromosome 9 Medium submetacentric Chromosome 2 136 million base pairs (largest) Submetacentric Second largest Chromosome 10 243 million base pairs Medium submetacentric 135 million base pairs Chromosome 3 Metacentric Chromosome 11 199 million base pairs Medium submetacentric 134 million base pairs Group B Chromosome: 4-5 Chromosome 12 Large Medium submetacentric Submetacentric with two arms very different in size 132 million base pairs Group D Chromosomes:13-15 Medium size Acrocentric with satellites Chromosome 13 Chromosome 4 Medium acrocentric Submetacentric With stalk 191 million base pairs 113 million base pairs Chromosome 5 Chromosome 14 Submetacentric Medium acrocentric 181 million base pairs With stalk 105 million base pairs Flores, Keziah Hymn S.  CYTOGENETICS Chromosome 15 Chromosome 22 Medium acrocentric Small acrocentric With stalk Second smallest chromosome 100 million base pairs With stalk 49 million base pairs Group E Chromosomes: 16-18 Y Chromosome Small Small acrocentric 16 is metacentric Without satellites 17 and 28 are submetacentric Largest in Group G 50 million base pairs Euploidy Condition of having a normal number of structurally normal chromosomes Chromosome 16 Small metacentric 90 million base pairs Chromosome 17 Small submetacentric Aneuploidy 81 million base pairs Any abnormal number of chromosomes that is not a multiple of the haploid number (23 chromosomes) Chromosome 18 Result of nondisjunction → failure of chromosomes to Small submetacentric separate normally during cell division (meiosis) 76 million base pairs o Trisomy – presence of an extra chromosome o Monosomy – absence of a single chromosome Group F Chromosomes: 19-20 Cause of Aneuploidy Small Metacentric Chromosome 19 Small metacentric 63 million base pairs Chromosome 20 Small metacentric 59 million base pair Group G Chromosomes: 21-22, Y Small Acrocentric 21 and 22 with satellites Chromosome 21 Smallest chromosome Acrocentric with satellite 46 million base pairs Flores, Keziah Hymn S.  CYTOGENETICS Polyploidy Heterochromatin Chromosome number is higher than 46 but is always an Tightly packed chromatin exact multiple of the haploid chromosome number of 23 Low gene density o Triploidy (3n) – a karyotype with 69 Constitutive heterochromatin chromosomes Facultative heterochromatin o Tetraploidy (4n) – a karyotype with 92 Closed chromatin conformation: repression chromosomes Chromosome Numbers of Some Plants and Animals: G-Banding Giemsa stain Dark bands = A-T Light bands = G-C Chromosomal Banding Staining Technique for chromosomes Comprised of alternating light and dark stripes (bands) Appear along its length after being stained with a dye R-Banding Reverse patterns of G bands Staining with Giemsa dye Dark bands = G-C Light bands = A-T Types of Chromosomal Banding G-banding R-banding Q-banding C-banding T-banding NOR banding Euchromatin Lightly packed chromatin Enriched in genes Active transcription Q-Banding Open chromatin conformation: activation Quinacrine stain Fluorescent pattern Dark bands = A-T Light bands = G-C Flores, Keziah Hymn S.  CYTOGENETICS C-Banding Dark bands – Constitutive heterochromatin Centromeric T-Banding Staining telomeric regions Giemsa stain or Acridine orange NOR Staining Identifies genes for ribosomal RNA that were active in a previous cell cycle Nucleolar Organizing Region Silver Staining methos NORs are located on the short arms of the acrocentric chromosomes 13, 14, 15, 21, 22 Flores, Keziah Hymn S.