Biology 2- UH BIOL 1362- Meiosis
Biology 2- UH BIOL 1362- Meiosis BIOL 1362
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This 4 page Class Notes was uploaded by Alexis Clowtis on Thursday February 25, 2016. The Class Notes belongs to BIOL 1362 at University of Houston taught by CHEEK in Spring 2016. Since its upload, it has received 26 views. For similar materials see Biology 2 in Biology at University of Houston.
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Date Created: 02/25/16
Biology 1362- 8:30am TTH SW 102 Doctor Ann Cheek- 2/23/16 Mechanism of Meiosis Meiosis I Separation of homologous chromosomes during formation of gametes (Figure) Replicate everything, separate homologous chromosomes then separate copies in meiosis II Prophase I - Homologous chromosomes held together by synaptonemal complex-proteins - Crossing over- chunks of DNA are swapped between non-sister chromatids o Enzymes cut DNA then after switch, other enzymes glue pieces to other chromosomes o If crossing over happened between sister chromatids, genetic info wouldn’t change - Chiasma (singular)- point t which crossover occurs (pl. chiasmata) - Crossing over during prophase I produces recombinant chromosomes: chromosomes that contain genes from both parents o You mix what your parents gave you TO PASS ON TO OFFSPRING because this is in making gametes - Nuclear envelope breaks down - Spindle forms and microtubules attach to kinetochores Biology 1362- 8:30am TTH SW 102 Doctor Ann Cheek- 2/23/16 Metaphase I - Kinetochores of homologs (1/2 of homologous pair; one of each homologous pair) are attached to microtubules from opposite poles Anaphase I - Homologs separate (but chromatids still together) - Homologs move along spindle to opposite poles Telophase I - 2 haploid nuclei (separate at end of cytokinesis to 2 haploid cells) - 2 sister chromatids per chromosome - Complete haploid set of chromosomes at each pole - Identified as 2 chromosomes because 1 chromosome per cell of each number, 4 unique DNA molecules “That’s info for chromosome 2, but we have 4 different codes for same characters” Cytokinesis - Cytoplasm divides - Result: 2 haploid (1n) daughter cells (Further explanation on pg. 198 of textbook where Meiosis I and II are together) Biology 1362- 8:30am TTH SW 102 Doctor Ann Cheek- 2/23/16 Meiosis II: separation of sister chromatids Prophase II - New spindle forms - Microtubules attach to kinetochores Anaphase II - Chromatids separate and move along spindle to opposite poles Telophase II and Cytokinesis - Nuclear envelope reforms - Chromosomes relax - Each nucleus contains 1 copy of each chromosome - Cytoplasm is divided Group activity Notes: Enucleated egg= egg without a nucleus so sperm is the only one contributing genetic material; because they both were normal, this organism only needs 18 chromosomes to survive (sperm has 18, egg has 18, zygote only needs 18 to survive) Biology 1362- 8:30am TTH SW 102 Doctor Ann Cheek- 2/23/16 Additional notes from textbook: Mitosis Meiosis DNA Replication Interphase- S phase Interphase- S phase Number of divisions 1 2 Synapsis of homologous ---does not occur--- Occurs during prophase I chromosomes along with crossing over between nonsister chromatids Number of daughter cells 2 diploid, clones 4 haploid, each genetically different from parent cell and each other Role in animal body Body cells; epithelium (get Produces gametes; a scratchhealing) introduces genetic variability *MEIOSIS IS FOR GAMETES ONLY NOT BODY CELLS* decides what offspring will pass on to their offspring \ Genetic variation among offspring occurs because of independent assortment of chromosomes, crossing over, and fertilization