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Cellular Reproduction Ch. 8 (8-1) Chromosomes • DNA & protein in a coiled, rod-shaped form that occurs during cell division – Uncoiled form is chromatin • Histone: protein DNA wraps around – Maintains shape & tight packing Chromosomes (cont.) • 2 sister chromatids – Exact copies of each other • Connected by centromere • Cell division separates chromatids • Each new cell gets 1 copy of each chromosome Chromosome # • Each species has characteristic # of chromosomes in each cell Ameba 50 Goldfish 94 Alligator 32 Garden Pea 14 Brown bat 44 Grasshopper 24 Bullfrog 26 Horse 64 Carrot 18 Human 46 Cat 32 Lettuce 18 Chicken 78 Onion 16 Chimpanzee 48 Redwood 22 Corn 20 Sand dollar 52 Earthworm 36 Fruit fly 8 Sex Chromosomes • Determine sex of organism & may carry genes for other characteristics – Humans (X or Y) • Autosomes: all other chromosomes besides sex – Humans = 44 (other 2 are sex) Homologous Chromosomes • Homologues: pairs of chromosomes – Same size, shape, & genes – Different from other homologues • In sexual reproduction, organism receives 1 copy of each autosome from each parent Karyotype • Photomicrograph of chromosome in a living cell – Humans: 22 homologues & 2 sex chromo.’s Diploid • (2n): cells that contain 2 sets of chromosomes – Humans 2n is 46 • Haploid (1n): cells that contain 1 chromosome of each hom. pair – Sex chromo.’s Reproduction • When sperm (1n) & egg (1n) combine to make 1st cell of new organism, the new cell is diploid (2n) (8-2) Cell Division • Process in which cells produce offspring cells • Why do cells divide? – Size is limited – Replace damaged cells – Growth Prokaryotic Cell Division • Binary fission: division of prokaryotes into 2 offspring cells • 3 stages: 1. Chromosome copied 2. Cell grows 3. Cell wall forms & cell splits into 2 new identical cells Eukaryotic Cell Division • Mitosis (Growth Div.): division of cell producing 2 identical daughter cells – 2n 2n • Meiosis (Reduction Div.): division of cell producing 4 haploid daughter cells – 2n 1n The Cell Cycle 1. Interphase • • • G1 S G2 2. Cell Division • • Mitosis (M phase): nucleus divides Cytokinesis: cytoplasm divides Interphase • Cells in this stage most – Time b/w cell divisions • 3 stages – G1: offspring grow to mature size • G0: leave cycle, usually when mature – S: DNA replication – G2: cell preps for cell division DNA Replication • After replication, each double stranded molecule contains 1 old strand & 1 new strand of DNA cell doubles in size enzymes and ribosomes and mitochondria double in number cell growth Cytokinesis Mitosis DNA replicates Growth and preparation for mitosis rapid growth, synthesizing necessary enzymes and structures for mitosis Step 1: Prophase • • • • Chromo.’s form from chromatin Nuclear membrane disassembles Centrioles move to pole Spindle fibers form Step 2: Metaphase • Fibers line chromo.’s up in the middle of the cell • Metaphase plate Step 3: Anaphase • Sister chromatids separate (become individual chromo.’s) & move to opposite poles Step 4: Telophase • • • • Spindle fibers disappear Nuclear membrane reforms Chromo.’s go back to chromatin 2 nuclei per 1 cell Cytokinesis • Division of cytoplasm – Animals - cell membrane pinches – Plants - cell plate forms • Results: 2 identical daughter cells Cancer • Uncontrolled growth of cells • Don’t respond normally to body’s control mechanisms • Mutations can interfere w/ ability to slow or stop cell cycle Brain Cancer (8-3) Meiosis • Nuclear division that reduces the # of chromo.’s in new cells to ½ the # of the original cell 2 Stages: 2n Meiosis I n n Meiosis II Results in 4 haploid cells n n n n Interphase • Same as mitosis • 3 stages: G1, S, G2 • Prep for meiosis I Meiosis I • 2 haploid cells form from 1 diploid cell • “Reduction Division” Step 1: Prophase I • Chromo.’s form from chromatin • Nuclear membrane breaks down • Centrioles move to poles • Spindle fibers form • Synapsis occurs Definitions • Synapsis: pairing of homologues to form tetrad • Crossing over: chromatids of hom. chromo.’s twist & trade places to exchange DNA (genetic recombination) Step 2: Metaphase I • Tetrads line up randomly at the metaphase plate • Spindle fibers attach Step 3: Anaphase I • Tetrads split & each homologue is moved toward opposite pole • Independent assortment: random separation of maternal & paternal chromo.’s – Genetic variety Step 4: Telophase I • Nuclear membrane reforms • Spindle fibers & centrioles disappear • Each nucleus now has haploid # of chromo.’s Cytokinesis I • Cytoplasm splits to produce 2 haploid daughter cells Meiosis II • No interphase b/w meiosis I & II • 4 haploid cells produced from 2 haploid cells • Exact same process as mitosis Step 1: Prophase II • Spindle fibers form & begin to move towards middle of the cell Step 2: Metaphase II • Chromo.’s move to midline Step 3: Anaphase II • Chromatids separate & move to opposite poles Step 4: Telophase II • Nuclear membrane forms around chromo.’s in each of 4 new cells Cytokinesis II • End result = 4 haploid cells Gamete Production • Gamete: haploid sex cells – egg & sperm • Oogenesis: egg production – 1 large egg & 3 polar bodies • Spermatogenesis: sperm production – 4 sperm Sexual Reproduction • Each parent contributes genes & offspring is different from any other member of their species (except id. twin) • Gives offspring better chance of surviving in a changing environment Asexual Reproduction • Offspring is an exact copy of parent – All cells form through mitosis • Mainly occurs in prokaryotes – Bacteria, molds, algae, & protozoa Asexual Reproduction Regeneration Spores Budding Binary Fission Mitosis vs. Meiosis • Mitosis – 1 division – 2 daughter cells – Exact copies of parent cells – Diploid to diploid – Purpose: • Growth • Repair • Asexual reproduction • Meiosis – 2 divisions – 4 daughter cells – Each unique – Diploid to haploid – Purpose: • Make gametes • Genetic variation