Supplemental File S2. Why Meiosis Matters
Transcription
Supplemental File S2. Why Meiosis Matters
Introduction to the Case of the Mysterious Snake To preserve the animations, please be sure to work through the slide show before editing; movements will not appear on the slide itself – only during a slide show Notes about what to say are included on the slide notes area Professor Chiszar’s Big Surprise snakes Include a nice photo of a timber rattlesnake I had a photo of Prof. Chiszar in his lab, but the url is no longer available – I suggest adding a photo of someone handling snakes in a lab setting Timber rattlesnake Crotalus horridus For a nice photo, see: http://animals.timduru.org/dirlist/snake/TimberRattlesnake_01-OnSand.jpg http://animals.timduru.org/dirlist/snake/TimberRattlesnake_01-OnSand.jpg Timber rattlesnake: Crotalus horridus For a nice video see http://www.youtube.com/watch?v=EMaBH7EKYMU The newborn snake pops out at about 2:30 on the video http://www.youtube.com/watch?v=EMaBH7EKYMU Timber rattlesnake: Crotalus horridus For an interesting video see: http://www.youtube.com/watch?v=y7B8L47jP D0 http://www.youtube.com/watch?v=y7B8L47jPD0 Professor Chiszar’s big surprise For an nice photo see: http://www.bbc.co.uk/nature/adaptations/Ov oviviparity http://www.bbc.co.uk/nature/adaptations/Ovoviviparity One more surprise! It’s a boy! What would you like to ask Prof. Chiszar about this baby snake? Where do babies come from? • Ultimately: from cells • How do cells reproduce? Mitosis A Primer on Basic Features of Mitosis & Meiosis To preserve the animations, please be sure to work through the slide show before editing mitosis • Metaphase: homologous chromosomes independently line up • Produces two genetically identical nuclei (two genetically identical daughter cells after cell division) nucleus nucleus cell nucleus nucleus nucleus nucleus Original nucleus Daughter nucleus Daughter nucleus Could the baby snake be produced by mitosis? Well, where do baby snakes usually come from? For a nice photo of fertilization, see http://www.webmd.com/baby/ss/slideshowconception http://www.webmd.com/baby/ss/slideshow-conception meiosis • DNA replicates once, but cell divides twice – First meiosis: duplicated, homologous chromosomes pair up at metaphase so each cell gets one set of duplicated chromosomes – Second meiosis: duplicated chromosomes line up independently at metaphase so each cell gets one sister chromatid (i.e. all cells are haploid and have only one copy of each chromosome) • Produces gametes with one set of chromosomes – Four gametes (sperm) or one big gamete (egg) & three tiny cells called polar bodies nucleus nucleus cell nucleus nucleus nucleus nucleus nucleus nucleus nucleus Mitosis Cell division 2X Meiosis Cell division Cell division Cell division Cell division meiosis sex chromosomes X Y XY, male X Y X X Y Y X X Y Y X X Y Y X Y X X Y Y Genetic Sex Determination In Mammals Mitosis X X Y Y X X X Y Cell division X XY Meiosis X Y Cell division X Y Cell division X X X Cell division Cell division 2X XX XY X X Y Y X X X X Genetic Sex Determination In Birds,Reptiles Mitosis Z Z W W Z Z Z W Cell division Z ZW Meiosis Z W Cell division Z W Z Cell division Z Z Cell division Cell division 2X ZZ ZW Z Z W W Z Z Z Z Parthenogenesis in Vertebrates • Production of offspring from unfertilized eggs Some Variations in Vertebrate Reproduction Homologs Parthenogenesis Gynogenesis Ab M1 (P1 (P3 aB M2 P2) P4) Haplotype Haplotype M1 M2 M1 M2 Defective Meiosis Defective meiosis Diploid egg Diploid egg M1 M2 Hybridogenesis Diploid egg M1 P1 P1 P2 Fertilization M1 M2 P1 or P2 M1 M2 Paternal genome eliminated Defective meiosis Haploid egg (paternal genome eliminated) Diploid egg P3 P4 Fertilization M1 M1 P3 or P4 Development Development Development M1 M2 M1 M2 M1 P3 or M1 P4 P3 or P4 Parthenogenesis in Vertebrates Where might meiosis “go wrong” so that a diploid egg cell is produced? Mitosis A AA, Bb Genotype of Diploid Parent Cell B A B A A B b Meiosis A A b B Cell division b b A A Cell division Cell division A A A A A A A A B B b b b b B B Cell division Cell division 2X AA, Bb A B A B A b A b A b A b A B A B Bonus slides – showing chromosomes with alleles mitosis with alleles A A b AA, Bb B A A A A b b B B A A A A b b B B AA, Bb A A A A B b A A AA, Bb AA, Bb b b B B meiosis with alleles A A B AA, Bb b A A b B A A A A b b B B A A A A b b B B A A A A AA, Bb b b A, b B B A, b A, B A, B A A A A AA, Bb B B A, B b b A, B A, b A, b Mitosis A AA, Bb Genotype of Diploid Parent Cell B A B A A B b Meiosis A A b B Cell division b b A A Cell division Cell division A A A A A A A A B B b b b b B B Cell division Cell division 2X AA, Bb A B A B A b A b A b A b A B A B