Transcript Meiosis I
Chromosomes and Mitosis/Meiosis Info. On Chromosomes Vocabulary 1. Chromatin: DNA and Protein DNA existing as thin, uncoiled strands This looks like spaghetti in the nucleus. 2. Chromosome: A visible carrier of the genetic information. Chromosomes contain many genes. Every human cell contains 23 pairs of chromosomes. Females: XX Males: XY 3. Chromatids: are identical copies of a chromosome. sister chromatids contain the same genes and same alleles. 4. Centromere: Point at which the pair of chromatids are attached. 5. Allele: alternative forms of a gene 6. Autosomes/somatic: body cells; chromosome pairs 1-22 7. Sex Chromosomes: 23rd pair- determines sex of child Human Karyotype Homologous chromosomes: Each pair is similar in size, shape, and genetic content. Steps in the cell cycle Cell Cycle 1. Interphase: G1, S, G2 2. Prophase 3. Metaphase Mitosis 4. Anaphase 5. Telophase 6. Cytokinesis These are the steps in the entire cell cycle. • Each new cell has 46 chromosomes. • Cells are identical to each other: Called daughter cells Mitosis if Animal cells Mitosis in Plant Cells Interphase • • • • • • • Period of cell growth Not a true stage of mitosis Can’t see chromosomes at first – duplication 90% of time G1: Normal Growth Phase S: DNA Duplicates and Pairs together G2: all other cell structures duplicate Prophase - Chromosomes become visible Nuclear membrane dissolves In animal cells, 2 centrioles move to opposite ends of cell Spindle fibers between centrioles stretch across the call Metaphase - Double stranded chromosomes line up around center of cell - Each centromere becomes attached to a spindle fiber - Spindle fibers link the chromatids of each chromosome to opposite poles Anaphase • Each centromere divides • Two chromatids (now called chromosomes) move toward opposite poles as spindle fibers attached to them shorten Telophase • Centrioles and spindle fibers start to disappear • Chromosomes uncoil/stretch out and become hard to see • Nuclear membrane forms around each mass of chromosomes – forms new nuclei • Cytokinesis begins - cytoplasm separates into 2 new cells Cytokinesis: The division of the cytoplasm after Mitosis (division of the nucleus) occurs. Final step in cell cycle. • Animal Cell – Cytoplasm pinches apart • Plant Cell – CELL PLATE forms between cells – before cell walls form Checkpoints 1. G1 checkpoint: decides of cell will divide a. S phase- Interphase (where DNA is copied). When its not the right conditions, cells will exit S phase and stay in resting period forever. Cells such as brain and some nerve cells stay in resting period and never divide. 2. DNA synthesis (G ) checkpoint: Replicated DNA is checked for errors. 3. Mitosis checkpoint: Triggers exit from mitosis. Signals G1 phase. Cancer 1. Uncontrolled growth of cells. 2. Genes contain info needed to make the proteins that regulate cell growth and division. Mutations of these genes can cause the proteins to malfunction and normal cell growth and regulation is disrupted. 3. Mutations cause overproducing growth-promoting molecules, speeding up the cell cycle. (stepping on the accelerator) 4. Inactivating the proteins that slow or stop the cell cycle (taking away the brakes) 5. Benign: tumors in which cancer cells remained in original site, can be removed successfully with out individuals having cancer. Inability to Metastasize (spread). Most are not harmful. Can be removed 6. Malignant: Cancerous tumors. They will Metastasize causing cancer. Treated with Radiation and Chemotherapy. MEIOSIS! (p142) • http://www.cellsalive.com/meiosis.htm a.Two Parts: Meiosis I and Meiosis II b.Meiosis I 1. Prophase 1: Nucl. Mem. Goes away, Nucleolus goes away, centrioles form spindles, Forms XX Tetrad , crossing over occurs___________ 2. Metaphase 1: Chromosome PAIRS line up in the middle 3. Anaphase 1: Chromosome pairs go towards centrioles at opposite ends of the cell. 4. Telophase1: Chromosomes are at opposite ends and the cytoplasm divides. (nucleolus comes back, nucleus comes back etc… 5. cytokinesis1. Cytoplasm splits into 2 genetically different cells. (diploid Cells= 46) CROSSING OVER • When portions of a chromatid (one of a pair of strands of DNA) on one homologous chromosome are broken & exchanged with the corresponding portions on one of the chromatids of the other homologous chromosome. • MEIOSIS II a. Prophase 2: nucl. Mem/Nucleolus goes away, spindles form b. Metaphase 2: Chromosomes line up in the middle c. Anaphase 2. Chromosomes split at centromere Move to centrioles d. Telophase 2: nucleolus/ nuc. Mem. Comes back, spindles go away, cell starts to split e. Cytokinesis 2: cytoplasm splits into 4 genetically different cells. (Haploid= 23) http://www.youtube.com/watch?v=JKXAdwCibsA&feature=related http://www.youtube.com/watch?v=35ncSrJOwME&feature=related 3:34 MEIOSIS CONTRIBUTES TO GENETIC VARIATION 3 Mechanisms make key contributions to genetic variation in Meiosis: 1. 2. 3. INDEPENDENT ASSORTMENT: - Random distribution of homologous chromosomes during Meiosis - 8 million different gene combinations! CROSSING OVER RANDOM FERTILIZATION: - 70 trillion possible outcomes! Independent Assortment GAMETE FORMATION IN MALE/FEMALE ANIMALS (p146) • SPERMATOGENESIS - Process by which sperm are produced in male animals - Occurs in Testes - Resulting 4 Haploid cells = SPERM • OOGENESIS - Process by which gametes are produced in female animals - Occurs in Ovaries - Resulting in larger egg or OVUM with most of the cytoplasm to nourish developing organism. CLONE - Produced by Asexual Reproduction – Genetically identical to its parents! Parthenogenesis! - New individual develops from an unfertilized egg (Ex: Drones – Bees) a form of reproduction in which the ovum develops into a new individual without fertilization. Natural parthenogenesis has been observed in many lower animals. In many social insects, such as the honeybee and the ant, the unfertilized eggs give rise to the male drones and the fertilized eggs to the female workers and queens. It has also been observed in some snakes, fish, and monitor lizards.