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 Connected by centromere 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: Chromosome copied Cell grows 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 Interphase Cell Division G1 S G2 Mitosis (M phase): nucleus divides Cytokinesis: cytoplasm divides

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

DNA Replication After replication, each double stranded molecule contains 1 old strand & 1 new strand of DNA

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 Results: 2 identical daughter cells 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: Meiosis I Meiosis II Results in 4 haploid cells 2n n 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 Oogenesis: egg production 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 Budding Spores Binary Fission

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