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Cellular Reproduction
Ch. 8
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(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
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Chromosomes (cont.) 2 sister chromatids Connected by centromere
Exact copies of each other Connected by centromere Cell division separates chromatids Each new cell gets 1 copy of each chromosome
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Chromosome # Each species has characteristic # of chromosomes in each cell Ameba Goldfish Alligator Garden Pea Brown bat Grasshopper Bullfrog Horse Carrot Human Cat Lettuce Chicken Onion Chimpanzee Redwood Corn Sand dollar Earthworm Fruit fly
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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)
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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
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Karyotype Photomicrograph of chromosome in a living cell
Humans: 22 homologues & 2 sex chromo.’s
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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
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Reproduction When sperm (1n) & egg (1n) combine to make 1st cell of new organism, the new cell is diploid (2n)
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(8-2) Cell Division Process in which cells produce offspring cells
Why do cells divide? Size is limited Replace damaged cells Growth
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Prokaryotic Cell Division
Binary fission: division of prokaryotes into 2 offspring cells 3 stages: Chromosome copied Cell grows Cell wall forms & cell splits into 2 new identical cells
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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
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The Cell Cycle Interphase Cell Division G1 S G2
Mitosis (M phase): nucleus divides Cytokinesis: cytoplasm divides
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Interphase Cells in this stage most 3 stages Time b/w cell divisions
G1: offspring grow to mature size G0: leave cycle, usually when mature S: DNA replication G2: cell preps for cell division
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DNA Replication After replication, each double stranded molecule contains 1 old strand & 1 new strand of DNA
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Step 1: Prophase Chromo.’s form from chromatin
Nuclear membrane disassembles Centrioles move to pole Spindle fibers form
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Step 2: Metaphase Fibers line chromo.’s up in the middle of the cell
Metaphase plate
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Step 3: Anaphase Sister chromatids separate (become individual chromo.’s) & move to opposite poles
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Step 4: Telophase Spindle fibers disappear Nuclear membrane reforms
Chromo.’s go back to chromatin 2 nuclei per 1 cell
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Cytokinesis Division of cytoplasm Results: 2 identical daughter cells
Animals - cell membrane pinches Plants - cell plate forms Results: 2 identical daughter cells
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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
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(8-3) Meiosis Nuclear division that reduces the # of chromo.’s in new cells to ½ the # of the original cell
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2 Stages: Meiosis I Meiosis II Results in 4 haploid cells 2n n n n n n
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Interphase Same as mitosis 3 stages: G1, S, G2 Prep for meiosis I
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Meiosis I 2 haploid cells form from 1 diploid cell
“Reduction Division”
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Step 1: Prophase I Chromo.’s form from chromatin
Nuclear membrane breaks down Centrioles move to poles Spindle fibers form Synapsis occurs
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Definitions Synapsis: pairing of homologues to form tetrad
Crossing over: chromatids of hom. chromo.’s twist & trade places to exchange DNA (genetic recombination)
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Step 2: Metaphase I Tetrads line up randomly at the metaphase plate
Spindle fibers attach
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Step 3: Anaphase I Tetrads split & each homologue is moved toward opposite pole Independent assortment: random separation of maternal & paternal chromo.’s Genetic variety
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Step 4: Telophase I Nuclear membrane reforms
Spindle fibers & centrioles disappear Each nucleus now has haploid # of chromo.’s
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Cytokinesis I Cytoplasm splits to produce 2 haploid daughter cells
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Meiosis II No interphase b/w meiosis I & II
4 haploid cells produced from 2 haploid cells Exact same process as mitosis
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Step 1: Prophase II Spindle fibers form & begin to move towards middle of the cell
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Step 2: Metaphase II Chromo.’s move to midline
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Step 3: Anaphase II Chromatids separate & move to opposite poles
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Step 4: Telophase II Nuclear membrane forms around chromo.’s in each of 4 new cells
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Cytokinesis II End result = 4 haploid cells
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Gamete Production Gamete: haploid sex cells Oogenesis: egg production
egg & sperm Oogenesis: egg production 1 large egg & 3 polar bodies Spermatogenesis: sperm production 4 sperm
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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
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Asexual Reproduction Offspring is an exact copy of parent
All cells form through mitosis Mainly occurs in prokaryotes Bacteria, molds, algae, & protozoa
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Asexual Reproduction Regeneration Budding Spores Binary Fission
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Mitosis vs. Meiosis Meiosis Mitosis 2 divisions 1 division
4 daughter cells Each unique Diploid to haploid Purpose: Make gametes Genetic variation Mitosis 1 division 2 daughter cells Exact copies of parent cells Diploid to diploid Purpose: Growth Repair Asexual reproduction
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