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Meiosis A REDUCTION DIVISION TO PRODUCE GAMETES WHICH ULTIMATELY MAINTAINS A CONSISTENT CHROMOSOME NUMBER IN THE SPECIES PART 2 Prophase in Meiosis http://biowiki.ucdavis.edu/Genetics/Unit_II%3A_Replication,_Maintenance_and_Alteration_of_the_Genetic_Material/8._R ecombination_of_DNA/Meiotic_recombination https://creativecommons.org/licenses/by-nc-sa/3.0/us/ No changes have been made. Leptotene Stage of Prophase I in Meiosis Homologous Chromosome Pair Cell Membrane Paternal Sister Chromatids Centromere Drawing: Lynda Jones, MS, ONPRC Centromere Nuclear Membrane Maternal Sister Chromatids Zygotene Stage of Prophase I of Meiosis Synapsis http://commons.wikimedia.org/wiki/File:Tetrad.png http://creativecommons.org/licenses/by-sa/2.5/deed.en No changes were made Synapsis https://www.boundless.com/biology/textbooks/boundless-biology-textbook/meiosis-and-sexual-reproduction11/the-process-of-meiosis-92/meiosis-i-404-11631/images/fig-ch11-01-01/ http://creativecommons.org/licenses/by-sa/4.0/ No changes were made. Formation of the Sex Body in the Late Zygotene-Early Pachytene Stage of Prophase I of Meiosis in the Testes SRY Gene Paternal Y Sister Chromatids Pseudoautosomal Region (PAR) where the X and Y chromosomes synapse or forming a fused X and Y tetrad known as the sex body Centromeres Other PAR regions Maternal X Sister Chromatids SRY is the Sex-determining Region Y gene (also known as the TDF or Testis-Determining Factor gene). Drawing: Lynda Jones, MS, ONPRC Crossing Over - Pachytene Stage of Prophase I of Meiosis https://upload.wikimedia.org/wikipedia/commons/0/0e/Morgan_crossover_1.jpg Public Domain Frans Alfons Janssens (1865 – 1924) Discovered and described crossing- over in chromosomes during meiosis which he called ‘chiasmatypie’ - 1909 http://en.wikipedia.org/wiki/File:Frans_Janssens.jpg Public Domain Thomas Hunt Morgan (1866-1945) • Discovered sex-linked genes and did further work on crossing over based on Janssens’ work and provided the first true genetic interpretation of meiosis • Won Nobel Prize in Physiology or Medicine in 1933 “for his discoveries concerning the role played by the chromosome in heredity” http://www.nobelprize.org/nobel_prizes/medicine/ laureates/1933/ http://upload.wikimedia.org/wikipedia/commons/8/8f/Thomas_Hunt_Morgan.jpg Public Domain http://cnx.org/contents/[email protected]:57/Biology http://creativecommons.org No changes were made. Homologous Chromosomes in the Diplotene Stage of Prophase I of Meiosis Maternal Sister Chromatids Paternal Sister Chromatids Centromeres Drawing: Lynda Jones, MS, ONPRC Chiasmata https://en.wikibooks.org/wiki/Medical_Physiology/Cellular_Physiology/DNA_and_Reproduction#/media/File:Meiosis.png By Boumphreyfr (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) No changes were made. The Origin of Aneuploidy Gametes by Nondisjunction in Meiosis http://upload.wikimedia.org/wikipedia/commons/3/31/Mitotic_nondisjunction.png http://creativecommons.org/licenses/bysa/3.0/deed.en No changes have been made. The Origin of Aneuploidy Gametes by Nondisjunction at the First or Second Meiotic Division http://upload.wikimedia.org/wikipedia/commons/b/ba/Trisomy_due_to_nondisjunction_in_maternal_meiosis_1.png http://creativecommons.org/licenses/by-sa/3.0/deed.en No changes have been made.
