Mitosis and Meiosis PDF

12/11/2018 Cell Division: Mitosis & Meiosis Isolated DNA The cell cycle multiplies cells T...

12/11/2018 Cell Division: Mitosis & Meiosis Isolated DNA The cell cycle multiplies cells The Cell Cycle  The cell cycle is an ordered sequence of events for cell division  It consists of two stages – Interphase: duplication of cell contents – G1—growth, increase in cytoplasm – S—duplication of chromosomes – G2—growth, preparation for division – Mitotic phase: division – Mitosis—division of the nucleus – Cytokinesis—division of cytoplasm Copyright © 2009 Pearson Education, Inc. 1  12/11/2018 The large, complex chromosomes of eukaryotes duplicate with each cell Time Duration in the Cell Cycle division  Eukaryotic chromosomes are composed of chromatin – Chromatin = DNA + proteins – To prepare for division, the chromatin becomes highly compact, and the chromosomes are visible with a microscope – Early in the division process, chromosomes duplicate – Each chromosome appears as two sister chromatids, containing identical DNA molecules – Sister chromatids are joined at the centromere, a narrow region Copyright © 2009 Pearson Education, Inc. Number of chromosomes in Sister chromatids various organisms Centromere Electron micrograph of a duplicated chromosome. This electron micrograph provides a view of sister chromatids. 2  12/11/2018 Parts of a metaphase chromosomes Chromosome 1. Chromatin: duplication Heterochromatin - where the DNA is more condensed, and usually there is not much transcriptional activity. Some Sister heterochromatin will remain condensed Centromere chromatids throughout the cell cycle. Euchromatin - this is where the "active" genes are - usually this region is much less condensed. 2. Centromere: During mitosis, spindle fibers attach to the centromere via the kinetochore - a highly complex multiprotein structure that is Chromosome responsible for the actual events of distribution chromosome segregation (Anaphase) to 3. Chromosome arms daughter P arm cells Q arm Parts of a metaphase chromosomes Telomeres Human 4. Secondary constriction: chromosomes Organism Telomeric repeat Site of nucleolus formation and are called "Nucleolar Organizing Region.“ sequence (grey) capped by 5. Satellite Yeasts telomeres (white)  This is the blob-like terminal part of a chromosome extending beyond the secondary Saccharomyces cerevisiae G1–3T constrictions.  It is rounded or elongated. Schizosaccharomyces pombe G2–5TTAC  It is also called trabant. Protozoans 6. Telomere Tetrahymena GGGGTT  The telomere represents the tip of a linear chromosome, one at each end. Dictyostelium G1–8A  Each has many repeats of DNA sequences. Plant  It prevents the adhesion of one chromosome to another at the ends. Arabidopsis AGGGTTT  A telomere is necessary for a proper replication of a chromosome. Mammal  It is also necessary for the attachment of chromosomes to the inner side of the Human AGGGTT nuclear envelope. Telomerase is an enzyme which can make the telomerase longer. 3  12/11/2018 Types of Chromosomes based Telomeres and Aging on Centromere Position Kind Position of Shape at Over-all length of centromere anaphase chromosome arms Metacentric Median V Equal Submetacentric Submedian L or J Unequal Telocentric Terminal l Highly unequal Acrocentric Subterminal i Very unequal Polytene Chromosome Giant chromosome formed when multiple rounds of DNA replication produce many sister chromatids that remain synapsed together. Found in salivary gland cells in the larval stages of Drosophila Have characteristic light and dark banding patterns that can be used to identify chromosomal rearrangements and deletions. Dark banding frequently corresponds to inactive chromatin, whereas light banding is usually found at areas with higher transcriptional activity. 4  12/11/2018 Lampbrush Chromosome Found in the growing oocytes (immature eggs) of most animals, except mammals Organized into a series of chromomeres with large chromatin loops extended laterally giving a hairy ”lampbrush” appearance. Polytene chromosomes Present during Prophase I in Axarus Cell division is a continuum of dynamic Cell division is a continuum of dynamic changes changes  Mitosis progresses through a series of stages  A mitotic spindle is required to divide the – Prophase chromosomes – Metaphase – The mitotic spindle is composed of microtubules – Anaphase – It is produced by centrosomes, structures in the cytoplasm that – Telophase – Organize microtubule arrangement  Cytokinesis often overlaps telophase – Contain a pair of centrioles in animal cells – The role of centrioles in cell division is unclear -- Centrioles are absent in plant cells Copyright © 2009 Pearson Education, Inc. Copyright © 2009 Pearson Education, Inc. 5  12/11/2018 Stages of Mitosis INTERPHASE PROPHASE PROMETAPHASE Chromatin METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Centrosomes Early mitotic Centrosome Fragments (with centriole pairs) spindle of nuclear Kinetochore Nucleolus Metaphase Cleavage envelope plate furrow forming Nuclear Plasma Centromere Spindle Nuclear envelope membrane Chromosome, consisting microtubules Daughter envelope Spindle chromosomes forming Nucleolus of two sister chromatids 6  12/11/2018 Wall of Cell plate Daughter parent cell forming nucleus Cytokinesis Cell wall New cell wall Vesicles containing Cell plate Daughter cells cell wall material 7  12/11/2018 Allium cepa Chromosome Abberation Test for Genotoxicity Analysis Chromosomal aberrations induced by QPE herbicide in root tip cells of Allium cepa. (a) Stickiness; (b, c, d) Bridges. 8  12/11/2018 Test System Stages of Meiosis Meiosis I Meiosis II Prophase I Leptotene  The chromosomes are long, thin threads occurring in the diploid number. Zygotene  The homologous chromosomes begin to pair; pairing is exact. Pachytene  The chromosomes have contracted and thickened; each chromosome has doubled itself so that the chromosome pair at this stage consists of four strands. Crossing over takes place during this stage. Diplotene  Each pair of synapsed chromosomes begins to uncoil and can be seen to contain four chromatids, two per chromosome (bivalent). Diakinesis  The bivalents have dispersed in the nucleus; the chromosomes assume different shapes due to repulsion and chiasma attachments. 9 12/11/2018 10  12/11/2018 Gametogenesis Spermatogenesis DNA copy Ploidy number/ Cell type chromosomes Process entered by cell chromatids in human in human spermatogonium diploid (2N) / 46 2C / 46 spermatocytogenesis (mitosis) primary diploid (2N) / 46 4C / 46 spermatidogenesis (meiosis 1) spermatocyte two secondary haploid (N) / 23 2C / 46 spermatidogenesis (meiosis 2) spermatocytes four spermatids haploid (N) / 23 1C / 23 spermiogenesis four functional haploid (N) / 23 1C / 23 spermiation spermatozoids Fertilization 11  12/11/2018 Drosophila life cycle Alternation of Generation in Angiosperms Nondisjunction Chromosome Mutations 12  12/11/2018 Karyotyping Process Normal Human Karyotype Down Syndrome (Trisomy 21) Can changes in the number of chromosomes affect health and development? Trisomy is the presence of an extra chromosome in cells. Down syndrome is an example of a condition caused by trisomy. 13  12/11/2018 Patau Syndrome (Trisomy 13) Edward Syndrome (Trisomy 18) The baby has no eyes, no nose The baby has elongated skull, opening, and an elongated bulb short neck, short breastbone, hanging from forehead. malformed ears and mentally deficient Karyotype of Metafemale (47-XXX) Turner Syndrome 14  12/11/2018 Klinefelter Syndrome Richard Speck: A Wrong Case of Jacob Syndrome (44-XYY) Jacob Syndrome Speck systematically killed eight student nurses from South Chicago Community Hospital in Chicago, Illinois on July 14, 1966. 15  12/11/2018 Chromosomal Mosaicism Cri-du-chat Syndrome When an individual has two or more cell populations with a different chromosomal makeup, this situation is called chromosomal mosaicism. Philadelphia chromosome or Philadelphia translocation Robertsonian translocation associated with Chromosome 21 breaks off and attaches to chromosome 14 chronic myelogenous The person in which this happens (called a translocation carrier) is leukemia (cancer of normal because, in essence, he or she only has the material of two the white blood cells). chromosome 21s, but part of one of them just happens to be attached to chromosome 14. reciprocal However, their child can inherit three “doses” of chromosome 21 translocation between material because the child might receive both a normal chromosome 21 chromosome 9 and 22 and the chromosome 14 that has the extra chromosome 21 material, then the child would have Down syndrome. About 3-5% of Down syndrome cases occur this way. For many parents who have had a child with Down syndrome due to a translocation, there is a 3-12% chance of that couple having another child with Down syndrome because the parent could pass on both a normal chromosome 21 and the chromosome 14 that has the extra chromosome 21 material to any child of theirs. 16  12/11/2018 Cancer HeLa Cell Line When normal cells are damaged beyond repair, they are eliminated by apoptosis (A). Cancer cells avoid apoptosis and continue to multiply in an unregulated manner (B). Henrietta Lacks (August 1, 1920 – October 4, 1951) For more info about Henrietta Lacks visit http://redwood.mntm.org/studentsite/highschool/Thinkquest%20Entrance%20 Site/heLa/history.htm Reference Genomes ,Chromatin, and Chromosomes http://kc.njnu.edu.cn/swxbx/shuangyu/8.htm 17