Meiosis & Sexual Reproduction PDF

Meiosis & Sexual Reproduction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MITOSIS SP...

Meiosis & Sexual Reproduction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MITOSIS SPERMATOGENESIS 2n Primary spermatocyte 2n 2n Meiosis I 2n Secondary spermatocytes MITOSIS n Meiosis II spermatids 2n n Metamorphosis and maturation sperm n zygote OOGENESIS Primary oocyte 2n = 46 2n diploid (2n) Meiosis I MEIOSIS FERTILIZATION First haploid (n) polar body n = 23 n Secondary oocyte n n Meiosis II Meiosis II is completed Second after entry of sperm polar body n egg Fertilization cont'd n n sper m nucl egg eus fusion of sperm n zygote sperm nucleus and egg nucleus 2n 1 Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display Outline  Reduction in Chromosome Number  Homologous Pairs  Meiosis Overview  Genetic Variation  Crossing-Over  Independent Assortment  Fertilization  Phases of Meiosis  Meiosis I  Meiosis II  Meiosis Compared to Mitosis  Human Life Cycle  Changes in Chromosome Number and Structure 2 Meiosis: Halves the Chromosome Number  Special type of cell division  Used only for sexual reproduction  Halves the chromosome number prior to fertilization  Parents diploid  Meiosis produces haploid gametes  Gametes fuse in fertilization to form diploid zygote  Becomes the next diploid generation 3 Homologous Pairs of Chromosomes  In diploid body cells chromosomes occur in pairs  Humans have 23 different types of chromosomes  Diploid cells have two of each type  Chromosomes of the same type are said to be homologous  They have the same length  Their centromeres are positioned in the same place  One came from the father (the paternal homolog) the other from the mother (the maternal homolog)  When stained, they show similar banding patterns  A location on one homologue contains gene for the same trait that occurs at this locus on the other homologue  Although the genes may code for different variations of that trait  Alternate forms of a gene are called alleles 4 Homologous Chromosomes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. sister chromatids Nonsister duplication duplication chromatids kinetochore centromere chromosome homologous pair chromosome paternal chromosome maternal chromosome b. 5 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 6 Homologous Pairs of Chromosomes  Homologous chromosomes have genes controlling the same trait at the same position  Each gene occurs in duplicate  A maternal copy from the mother  A paternal copy from the father  Many genes exist in several variant forms in a large population  Homologous copies of a gene may encode identical or differing genetic information  The variants that exist for a gene are called alleles  An individual may have:  Identical alleles for a specific gene on both homologs (homozygous for the trait), or  A maternal allele that differs from the corresponding paternal allele (heterozygous for the trait) 7 Overview of Meiosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Four haploid daughter cells centrioles nucleolus sister chromatids synapsis centromere chromosome duplication 2n = 4 2n = 4 n=2 n=2 MEIOSIS I MEIOSIS II Homologous pairs Sister chromatids separate, synapse and then separate. becoming daughter chromosomes. 8 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Phases of Meiosis I: Prophase I & Metaphase I  Meiosis I (reductional division):  Prophase I  Each chromosome internally duplicated (consists of two identical sister chromatids)  Homologous chromosomes pair up – synapsis  Physically align themselves against each other end to end  End view would show four chromatids – Tetrad  Metaphase I  Homologous pairs arranged onto the metaphase plate 10 Phases of Meiosis I: Anaphase I & Telophase I  Anaphase I  Synapsis breaks up  Homologous chromosomes separate from one another  Homologues move towards opposite poles  Each is still an internally duplicate chromosome with two chromatids  Telophase I  Daughter cells have one internally duplicate chromosome from each homologous pair  One (internally duplicate) chromosome of each type (1n, haploid) 11 Phases of Meiosis I: Cytokinesis I & Interkinesis  Cytokinesis I  Two daughter cells  Both with one internally duplicate chromosome of each type  Haploid  Meiosis I is reductional (halves chromosome number)  Interkinesis  Similar to mitotic interphase  Usually shorter  No replication of DNA 12 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Genetic Variation: Crossing Over  Meiosis brings about genetic variation in two key ways:  Crossing-over between homologous chromosomes, and  Independent assortment of homologous chromosomes  Crossing Over:  Exchange of genetic material between nonsister chromatids during meiosis I  At synapsis, a nucleoprotein lattice (called the synaptonemal complex) appears between homologues  Holds homologues together  Aligns DNA of nonsister chromatids  Allows crossing-over to occur  Then homologues separate and are distributed to different daughter cells 14 Crossing Over Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. nucleoprotein lattice sister chromatids sister chromatids of a chromosome of its homologue A A a a Aa B B b b chiasmata of B b nonsister nhromatids 1 and 3 c C C c C c D D d d D d 1 34 1 2 3 1 2 3 4 2 Bivalent 4 Daughter forms Crossing-over chromosomes has occurred a. b. c. d. Courtesy Dr. D. Von Wettstein 15 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 16 Genetic Variation: Independent Assortment Independent assortment: When homologues align at the metaphase plate: Theyseparate in a random manner The maternal or paternal homologue may be oriented toward either pole of mother cell Causes random mixing of blocks of alleles into gametes 17 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Independent Assortment Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 19 Recombination Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © American Images, Inc/Getty Images 20 Genetic Variation: Fertilization  When gametes fuse at fertilization:  Chromosomes donated by the parents are combined  In humans, (223)2 = 70,368,744,000,000 chromosomally different zygotes are possible  If crossing-over occurs only once  (423)2, or 4,951,760,200,000,000,000,000,000,000 genetically different zygotes are possible 21 Genetic Variation: Significance  Asexual reproduction produces genetically identical clones  Sexual reproduction cause novel genetic recombinations  Asexualreproduction is advantageous when environment is stable  However, if environment changes, genetic variability introduced by sexual reproduction may be advantageous  Offspring adapt to that environment 22 Phases of Meiosis II: Similar to Mitosis  Metaphase II  Overview  Unremarkable  Virtually indistinguishable from mitosis of two haploid cells  Prophase II – Chromosomes condense  Metaphase II – Chromosomes align at metaphase plate  Anaphase II  Centromere dissolves  Sister chromatids separate and become daughter chromosomes  Telophase II and cytokinesis II  Four haploid cells  All genetically unique 23 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Meiosis I & II in Plant Cells (Cont.) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plant Cell at Interphase centrosome has centrioles kinetochore 2n = 4 Prophase I Metaphase I Anaphase I Homologous Chromosomes have duplicated. Homologous pairs align chromosomes separate Animal Cell Homologous chromosomes pair during Independently at the metaphase and move toward the poles. at Interphase synapsis and crossing-over occurs. plate. MEIOSIS I n=2 n=2 Prophase II Metaphase II Anaphase II Cells have one chromosome Chromosomes align Sister chromatids separate and from each homologous pair. at the metaphase plate. become daughter chromosomes. MEIOSIS II © Ed Reschke 25 Meiosis I & II in Plant Cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. n=2 Telophase I Interkinesis Daughter cells have one Chromosomes still chromosome from each homologous n=2 consist of two chromatids. pair. MEIOSIS I cont'd n=2 n=2 Telophase II Daughter cells Spindle disappears, nuclei Meiosis results in four form, and cytokinesis takes haploid daughter place. cells. MEIOSIS II cont'd © Ed Reschke 26 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 27 Meiosis vs. Mitosis  Meiosis  Mitosis  Requires two nuclear  Requires one nuclear divisions division  Chromosomes synapse and  Chromosomes do not cross over synapse nor cross over  Centromeres survive  Centromeres dissolve in Anaphase I mitotic anaphase  Halves chromosome  Preserves chromosome number number  Produces four daughter  Produces two daughter nuclei nuclei  Produces daughter cells  Produces daughter cells genetically different genetically identical to from parent and each parent and to each other other  Used for asexual  Used only for sexual reproduction and growth reproduction 28 Meiosis Compared to Mitosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Telophase I Daughter cells are forming and will go on to divide again. n=2 Daughter cells Sister chromatids separate and become 2n = 4 daughter chromosomes. Four haploid daughter cells. Their nuclei are genetically n=2 Prophase I Metaphase I Anaphase I n=2 different from the parent cell. Synapsis and Homologous pairs align Homologous chromosomes crossing-over independently at the metaphase plate. separate and move towards the poles. MEIOSIS I occur. MEIOSIS I cont'd MEIOSIS II Daughter cells Two diploid daughter cells. 2n = 4 Telophase Their nuclei are genetically Daughter cells identical to the parent cell. Prophase Metaphase Anaphase are forming. Chromosomes align Sister chromatids separate and at the metaphase become daughter chromosomes. MITOSIS cont'd MITOSIS plate. 29 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 30 Meiosis I Compared to Mitosis 31 Meiosis II Compared to Mitosis 32 Life Cycle Basics: Plants  Haploid multicellular “individuals” alternate with diploid multicellular “individuals”  The haploid individual:  Known as the gametophyte  May be larger or smaller than the diploid individual  The diploid individual:  Known as the sporophyte  May be larger or smaller than the haploid individual  Mosses are haploid most of their life cycle  Ferns & higher plants have mostly diploid life cycles  In fungi and most algae, only the zygote is diploid  In plants gametes are produced by haploid individuals  Plants have both haploid and diploid phases in their life cycle 33 Life Cycle Basics: Animals  In familiar animals:  “Individuals” are diploid; produce haploid gametes  Only haploid part of life cycle is the gametes  The products of meiosis are always gametes  Meiosis occurs only during gametogenesis  Production of sperm  Spermatogenesis  All four cells become sperm  Production of eggs  Oogenesis  Only one of four nuclei get cytoplasm 34 The Human Life Cycle  Sperm and egg are produced by meiosis  A sperm and egg fuse at fertilization  Results in a zygote  The one-celled stage of an individual of the next generation  Undergoes mitosis  Results in multicellular embryo that gradually takes on features determined when zygote was formed  All growth occurs as mitotic division  As a result of mitosis, each somatic cell in body  Has same number of chromosomes as zygote  Has genetic makeup determined when zygote was formed 35 The Human Life Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MITOSIS 2n 2n 2n MITOS IS 2n zygote 2n = 46 diploid (2n) MEIOSIS FERTILIZATION haploid (n) n = 23 n n egg sperm 36 Gametogenesis in Mammals Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. SPERMATOGENESIS Primary spermatocyte 2n Meiosis I Secondary spermatocytes n Meiosis II spermatids n Metamorphosis and maturation sperm n OOGENESIS Primary oocyte 2n Meiosis I First polar body n Secondary oocyte n Meiosis II Meiosis II is completed Second after entry of sperm polar body n Fertilization egg cont'd n sper m nucl eus n fusion of sperm nucleus and zygote egg nucleus 2n 37 Changes in Chromosome Number  Euploid is the correct number of chromosomes in a species.  Aneuploid is change in the chromosome number  Results from nondisjunction  Monosomy - only one of a particular type of chromosome,  Trisomy - three of a particular type of chromosome 38 Changes in Chromosome Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. pair of pair of homologous homologous chromosomes chromosomes Meiosis I nondisjunction normal nondisjunction Meiosis II normal Fertilization Zygote 2n 2n 2n + 1 2n - 1 2n + 1 2n + 1 2n - 1 2n - 1 a. b. 39 Trisomy  Trisome 21  Occurs when an individual has three of a particular type of chromosome  The most common autosomal trisomy seen among humans  Also called Down syndrome  Recognized by these characteristics:  short stature  eyelid fold  flat face  stubby finger  wide gap between first and second toes 40 Trisomy 21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. extra chromosome 21 a. b. a: © Jose Carrilo/PhotoEdit; b: © CNRI/SPL/Photo Researchers 41 Changes in Sex Chromosome  Result from inheriting too many or too few X or Y chromosomes  Nondisjunction during oogenesis or spermatogenesis  Turner syndrome (XO)  Female with single X chromosome  Short, with broad chest and widely spaced nipples  Can be of normal intelligence and function with hormone therapy  Klinefelter syndrome (XXY) – a male  Male with underdeveloped testes and prostate; some breast overdevelopment  Long arms and legs; large hands  Near normal intelligence unless XXXY, XXXXY, etc.  No matter how many X chromosomes, presence of Y renders 42 Changes in Sex Chromosome Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Turner syndrome b. Klinefelter syndrome a: Courtesy UNC Medical Illustration and Photography; b: Courtesy Stefan D. Schwarz, http://klinefeltersyndrome.org 43 Changes in Chromosome Structure  Changes in chromosome structure include:  Deletions  One or both ends of a chromosome breaks off  Two simultaneous breaks lead to loss of an internal segment  Duplications  Presence of a chromosomal segment more than once in the same chromosome  Translocations  A segment from one chromosome moves to a non- homologous chromosome  Follows breakage of two nonhomologous chromosomes and improper re-assembly 44 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 45 Changes in Chromosome Structure  Duplication A segment of a chromosome is repeated in the same chromosome  Inversion  Occursas a result of two breaks in a chromosome  The internal segment is reversed before re-insertion  Genes occur in reverse order in inverted segment 46 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Types of Chromosomal Mutation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a a a b b b b c + a c c d c d d d e e e e f d f f g e g g f a. Deletion b. Duplication g a a a a b l b l c m c m b b d n d n d c d c e o e o f p f p e e g q q g f f h r r h g c. Inversion g d. Translocation 48 Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 50 Types of Chromosomal Mutation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a a b b + h ion lost c c delet d d e e f f g g h b: Courtesy The Williams Syndrome Association a. b. 51 Types of Chromosomal Mutation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a s a s b t b t c c u u v translocation d d v e w e w f x f x g y g y h z h z a. b. b: American Journal of Human Genetics by N. B. Spinner. Copyright 1994 by Elsevier Science & Technology Journals. Reproduced with permission of Elsevier Science & Technology Journals in the format Textbook via Copyright Clearance Center 52 Review  Reduction in Chromosome Number  Meiosis Overview  Homologous Pairs  Genetic Variation  Crossing-Over  Independent Assortment  Fertilization  Phases of Meiosis  Meiosis I  Meiosis II  Meiosis Compared to Mitosis  Human Life Cycle  Changes in Chromosome Number and Structure 53  BIOLOGY Chapter 10: pp. 169 - 188 10th Edition Meiosis & Sexual Sylvia S. Mader Reproduction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MITOSIS SPERMATOGENESIS 2n Primary spermatocyte 2n 2n Meiosis I 2n Secondary spermatocytes MITOSIS n Meiosis II spermatids 2n n Metamorphosis and maturation sperm n zygote OOGENESIS Primary oocyte 2n = 46 2n diploid (2n) Meiosis I MEIOSIS FERTILIZATION haploid (n) First polar body n n = 23 Secondary n oocyte n Meiosis II Meiosis II is completed Second after entry of sperm polar body n Fertilization egg n cont'd sper n m egg nucl eus sperm n fusion of sperm zygote nucleus and egg nucleus 2n PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor 54 Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display