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Asexual Reproduction (Mitosis) 1 1 How do little elephants grow up to be BIG elephants? The process of asexual reproduction begins after a sperm fertilizes an egg. Skin cancer - the abnormal growth of skin cells - most often develops on skin exposed to the sun. Cell that reproduce by asexual reproduction reproduce constantly. Animated Cell Cycle http://www.cellsalive.com/mitosis.htm • Interphase • Prophase • Metaphase • Anaphase • Telophase & Cytokinesis chromatin: uncoiled DNA(noodles) chromatid: single, coiled piece of DNA, 1/2 a chromosome (dreadlock) chromosome: X-shaped pair of identical DNA pieces Homologous pairs: a set of two chromosomes (one from each parent) that have the same genetic traits but different versions Diploid: a cell with all necessary homologous pairs Haploid: a cell with no homologous pairs Note: Mitosis makes DIPLOID cells A cell grows, prepares for division, and divides to form 2 daughter cells FOUR phases: 1. G1 (gap 1) 2. S phase (synthesis, DNA replication) 3. G2 (gap 2) 4. M phase (mitosis) • • • • G1, S, and G2 phases occur Chromosomes are copied in S phase DNA appears as threadlike chromatin Cell is doing its “day job” and maintaining homeostasis (staying alive) Nucleus CELL MEMBRANE Cytoplasm Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Mitosis begins (divide nucleus and DNA) • Centrioles (animal cell only) move to opposite end of the cell. • Spindle fibers form • DNA - Chromatin becomes rod-like chromatids that combine with copy to form X-shaped chromosomes • Centrioles Chromosomes Spindle fibers Animal Cell Plant Cell Spindle fibers Centrioles Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm • Chromosomes attach to the spindle fibers in the middle single-file Centrioles Spindle fibers Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Chromosomes are pulled apart to opposite ends of the cell. • Each side now has a single copy of each chromatid • Centrioles Spindle fibers Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm • • • Two new nuclei form. Chromatids uncoil to form chromatin (threads rather than rods). Mitosis ends. Nuclei Chromatin Nuclei Animal Cell Plant Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm • • • The rest of the cell splits to create two daughter cells – each with its own nucleus and identical chromosomes. Plant Cells – new cell wall forms called a cell plate Animal cells – pinches inward to form a cleavage furrow Animal Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Interphase Plant Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Interphase 25 - Cell Division 26 26 Interphase (G1, S, G2) Mitosis Prophase Metaphase Anaphase Telophase Cytokinesis Interphase Prophase Metaphase Anaphase Telophase Cytokinesis Interphase Prophase Metaphase Anaphase Telophase Cytokinesis two daughter cells have identical copies of the parent cell’s DNA # of chromosomes is the same in both cells A microscope was used to examine onion root tips. 4 different fields (A, B, C, and D) were used. In each field, the cells in the mitotic phases were identified and counted. Cells in interphase were also counted. What does this data reveal? Area A Area B Area C Area D Total Interphase 30 23 34 22 109 Prophase 3 4 3 2 12 Metaphase 6 3 2 4 15 Anaphase 3 1 2 1 7 Telophase 0 2 1 1 4 A human cell has 46 individual chromatids in its cells. After the S phase of the cell cycle, how many chromosomes will the cell contain? How many homologous (or matching) pairs of chromosomes will the cell have at prophase?