Mitosis and Meiosis Asexual v. Sexual Reproduction Cell dIVISION Mitosis and Meiosis Asexual v. Sexual Reproduction

Cell Division “process where 1 cell splits into 2” Replaces somatic (body) cells in multicellular organisms Allows for multicelullar growth Allows for asexual reproduction in plants

Chromosome – rod shaped structure made up DNA and protein a. held together by centromere - holds chromatids together until they separate during division b. only found during cell division

Chromosome Number Human/animal chromosomes – sex chromosomes and autosomes Humans have 46 chromosomes in somatic cells Karyotype – used to examine an individual’s chromosomes

Haploid Diploid Reproductive cells (sperm and egg) Somatic cells (body-all other cells) ½ the # of chromosomes (23) Has ALL chromosomes (46) half the DNA Has ALL DNA N = haploid 2N = diploid

Cell Division in Prokaryotes Binary Fision – two identical cells are produced from one cell * division in bacteria

Cell Division in Eukaryotes Mitosis Meiosis Asexual Reproduction Sexual Reproduction Division of diploid cells (somatic cells) Division of haploid cells (reproductive cells) Results in 2 identical daughter cells Results in 4 haploid daughter cells 1 division 2 divisions

Cell Cycle “series of events leading to cell division” Interphase – occurs before mitosis begins - longest part of the cell cycle

Mitosis Asexual Reproduction Diploid cells split into 2 identical diploid cells Allows body cells to be replaced and cells to GROW

Phases of Mitosis 1. Prophase Chromatin coils to make chromosomes 2 pairs of centrioles move apart and spindle fibers appear 2 types of spindle fibers a. kinetochore fibers b. polar fibers

2. Metaphase Kinetochore fibers move chromosomes to the center (equator) of the cell

3. Anaphase Spindle fibers grab the centromeres of each chromosome and pull the chromatids apart Chromatids now separate (now called daughter chromosomes) and are pulled to the opposite poles

4. Telophase Spindle fibers disassemble and chromosomes return to a less tightly coiled chromatin state Nuclear envelope and membrane reappear Cytokinesis – splitting of the cytoplasm a. cleavage furrow b. 2 cells are equal in size c. each cell receives an identical copy of the original cell’s chromosomes

Cytokinesis “division of the cytoplasm” *animal cell – creates 2 new cells * Plant cell – forms cell plate

Meiosis “sexual reproduction” Fusing of 2 haploid gametes to form 1 diploid zygote

Stages 2 divisions a. Meiosis I

b. Meiosis II

Sources of Genetic Variation Crossing – over Fertilization Independent Assortment