Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 8 The Cellular Basis of Reproduction and Inheritance

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION 8.1 Like begets like, more or less Some organisms reproduce asexually –And their offspring are genetic copies of the parent and of each other LM 340  Figure 8.1A

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Other organisms reproduce sexually –Creating a variety of offspring Figure 8.1B

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.2 Cells arise only from preexisting cells Cell division is at the heart of the reproduction of cells and organisms –Because cells come only from preexisting cells

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.3 Prokaryotes reproduce by binary fission Prokaryotic cells –Reproduce asexually by cell division Colorized TEM 32,500  Prokaryotic chromosomes Figure 8.3B

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings THE EUKARYOTIC CELL CYCLE AND MITOSIS 8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division A eukaryotic cell has many more genes than a prokaryotic cell –And they are grouped into multiple chromosomes in the nucleus

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LM 600  Individual chromosomes contain a very long DNA molecule associated with proteins –And are visible only when the cell is in the process of dividing If a cell is not undergoing division –Chromosomes occur in the form of thin, loosely packed chromatin fibers Figure 8.4A

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Before a cell starts dividing, the chromosomes replicate –Producing sister chromatids joined together at the centromere TEM 36,000  Centromere Sister chromatids Figure 8.4B

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Cell division involves the separation of sister chromatids –And results in two daughter cells, each containing a complete and identical set of chromosomes Centromere Chromosome duplication Sister chromatids Chromosome distribution to daughter cells Figure 8.4C

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.5 The cell cycle multiplies cells The cell cycle consists of two major phases INTERPHASE S (DNA synthesis) G1G1 G2G2 Cytokinesis Mitosis MITOTIC PHASE (M) Figure 8.5

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Interphase (G 1, S and G 2 ) –Chromosomes duplicate and cell parts are made Mitotic phase (M phase) –Duplicated chromosomes are evenly distributed into two daughter nuclei

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.6 Cell division is a continuum of dynamic changes In mitosis, after the chromosomes coil up –A mitotic spindle moves them to the middle of the cell

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The sister chromatids then separate –And move to opposite poles of the cell, where two nuclei form Cytokinesis, in which the cell divides in two –Overlaps the end of mitosis

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The stages of cell division INTERPHASEPROPHASEPROMETAPHASE LM 250  Chromatin Centrosomes (with centriole pairs) Nucleolus Nuclear envelope Plasma membrane Early mitotic spindle Centrosome Centromere Chromosome, consisting ot two sister chromatids Spindle microtubules Kinetochore Fragments of nuclear envelope Figure 8.6 (Part 1)

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Spindle Metaphase plate Daughter chromosomes Nuclear envelope forming Cleavage furrow Nucleolus forming Figure 8.6 (Part 2)

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.7 Cytokinesis differs for plant and animal cells In animals –Cytokinesis occurs by a constriction of the cell (cleavage) Cleavage furrow SEM 140  Daughter cells Cleavage furrow Contracting ring of microfilaments Figure 8.7A

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings In plants –A membranous cell plate splits the cell in two Figure 8.7B TEM 7,500  Cell plate forming Wall of parent cell Daughter nucleus Cell wall New cell wall Vesicles containing cell wall material Cell plate Daughter cells

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.8 Anchorage, cell density, and chemical growth factors affect cell division Most animal cells divide –Only when stimulated, and some not at all

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Cells anchor to dish surface and divide. When cells have formed a complete single layer, they stop dividing (density- dependent inhibition). If some cells are scraped away, the remaining cells divide to fill the dish with a single layer and then stop (density-dependent inhibition). In laboratory cultures –Most normal cells divide only when attached to a surface They continue dividing –Until they touch one another Figure 8.8A

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Growth factors –Are proteins secreted by cells that stimulate other cells to divide After forming a single layer, cells have stopped dividing. Providing an additional supply of growth factors stimulates further cell division. Figure 8.8B

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.9 Growth factors signal the cell cycle control system A set of proteins within the cell –Controls the cell cycle

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Signals affecting critical checkpoints in the cell cycle –Determine whether a cell will go through the complete cycle and divide Control system G1G1 S G2G2 M G 1 checkpoint G 2 checkpoint M checkpoint G0G0 Figure 8.9A

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.11 Review of the functions of mitosis: Growth, cell replacement, and asexual reproduction When the cell cycle operates normally, mitotic cell division functions in –Growth LM 500  Figure 8.11A

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LM 700  Replacement of damaged or lost cells Figure 8.11B

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Asexual reproduction LM 10  Figure 8.11C

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings MEIOSIS AND CROSSING OVER 8.12 Chromosomes are matched in homologous pairs The somatic (body) cells of each species –Contain a specific number of chromosomes For example human cells have 46 –Making up 23 pairs of homologous chromosomes

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The chromosomes of a homologous pair –Carry genes for the same characteristics at the same place, or locus Chromosomes Centromere Sister chromatids Figure 8.12

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.13 Gametes have a single set of chromosomes Cells with two sets of chromosomes –Are said to be diploid (2n) Gametes, eggs and sperm, are haploid –With a single set of chromosomes (n)

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Sexual life cycles –Involve the alternation of haploid and diploid stages Mitosis and development Multicellular diploid adults (2n = 46) Diploid zygote (2n = 46) 2n2n Meiosis Fertilization Egg cell Sperm cell n Haploid gametes (n = 23) n Figure 8.13

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.14 Meiosis reduces the chromosome number from diploid to haploid Meiosis, like mitosis –Is preceded by chromosome duplication –Duplication only occurs before meiosis I But in meiosis –The cell divides twice to form four daughter cells

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The first division, meiosis I –Starts with synapsis, the pairing of homologous chromosomes In crossing over –Homologous chromosomes exchange corresponding segments Meiosis I separates each homologous pair –And produce two daughter cells, each with one set of chromosomes

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Meiosis II is essentially the same as mitosis –The sister chromatids of each chromosome separate –The result is a total of four haploid cells

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The stages of meiosis MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Centrosomes (with centriole pairs) Sites of crossing over Spindle Microtubules attached to kinetochore Metaphase plate Sister chromatids remain attached Nuclear envelope Chromatin Sister chromatids Tetrad Centromere (with kinetochore) Homologous chromosomes separate Figure 8.14 (Part 1)

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings PROPHASE II METAPHASE II ANAPHASE II TELOPHASE I AND CYTOKINESIS TELOPHASE II AND CYTOKINESIS Cleavage furrow Haploid daughter cells forming Sister chromatids separate MEIOSIS II: Sister chromatids separate Figure 8.14 (Part 2)

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings MitosisMeiosis Parent cell (before chromosome replication) Chromosome replication Chromosomes align at the metaphase plate Tetrads align at the metaphase plate Sister chromatids separate during anaphase Homologous chromosomes separate during anaphase I; sister chromatids remain together No further chromosomal replication; sister chromatids separate during anaphase II Prophase Metaphase Anaphase Telophase Duplicated chromosome (two sister chromatids) Daughter cells of mitosis 2n2n 2n2n Daughter cells of meiosis I n n n n 2n = 4 Tetrad formed by synapsis of homologous chromosomes Meiosis i Meiosis ii Prophase I Metaphase I Anaphase I Telophase I Haploid n = 2 Daughter cells of meiosis II 8.15 Review: A comparison of mitosis and meiosis Figure 8.15

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.16 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring Each chromosome of a homologous pair –Differs at many points from the other member of the pair

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Random arrangements of chromosome pairs at metaphase I of meiosis –Lead to many different combinations of chromosomes in eggs and sperm Combination 1 Combination 2 Combination 3 Combination 4 Gametes Metaphase II Two equally probable arrangements of chromosomes at metaphase I Possibility 1Possibility 2 Figure 8.16

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Random fertilization of eggs by sperm –Greatly increases this variation

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.17 Homologous chromosomes carry different versions of genes The differences between homologous chromosomes –Are based on the fact that they can bear different versions of a gene at corresponding loci Tetrad in parent cell (homologous pair of duplicated chromosomes) ec EC White Pink ec ec EC EC Meiosis BlackBrown Chromosomes of the four gametes Eye-color genes Coat-color genes Brown coat (C); black eyes (E) White coat (C); pink eyes (e) Figure 8.17A Figure 8.17B

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.18 Crossing over further increases genetic variability Genetic recombination –Which results from crossing over during prophase I of meiosis, increases variation still further Figure 8.18A Chiasma Tetrad Centromere TEM 2,200 

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE 8.19 A karyotype is a photographic inventory of an individual’s chromosomes A karyotype –Is an ordered arrangement of a cell’s chromosomes

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CONNECTION 8.20 An extra copy of chromosome 21 causes Down syndrome A person may have an abnormal number of chromosomes (2n – 1 or 2n + 1) –Which causes problems

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Down syndrome is caused by trisomy 21 –An extra copy of chromosome 21 5,000  Figure 8.20AFigure 8.20B

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8.21 Accidents during meiosis can alter chromosome number Abnormal chromosome count is a result of nondisjunction –The failure of homologous pairs to separate during meiosis I –The failure of sister chromatids to separate during meiosis II

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Nondisjunction in meiosis I Normal meiosis II Gametes n  1 n  1 Number of chromosomes Nondisjunction in meiosis II Normal meiosis I Gametes n  1n  1 n n Number of chromosomes Figure 8.21A Figure 8.21B

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Fertilization after nondisjunction in the mother Sperm cell Egg cell n (normal) n + 1 Zygote 2n + 1 Figure 8.21C

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CONNECTION 8.22 Abnormal numbers of sex chromosomes do not usually affect survival Nondisjunction can also produce gametes with extra or missing sex chromosomes –Leading to varying degrees of malfunction in humans but not usually affecting survival Figure 8.22A Poor beard growth Breast Development Under-developed testes Figure 8.22B Characteristic facial features Web of skin Constriction of aorta Poor breast development Under developed ovaries

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Human sex chromosome abnormalities

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CONNECTION 8.23 Alterations of chromosome structure can cause birth defects and cancer Chromosome breakage can lead to rearrangements –That can produce genetic disorders or, if the changes occur in somatic cells, cancer

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Deletions, duplications, inversions, and translocations Deletion Duplication Inversion Homologous chromosomes Reciprocal translocation Nonhomologous chromosomes “Philadelphia chromosome” Chromosome 9 Chromosome 22 Reciprocal translocation Activated cancer-causing gene Figure 8.23A Figure 8.23C Figure 8.23B