Introduction to the Case of the Mysterious Snake

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/Timber. Rattlesnake_01 -On. Sand. jpg

Timber rattlesnake: Crotalus horridus For a nice video see http: //www. youtube. com/watch? v=EMa. BH 7 EKYMU The newborn snake pops out at about 2: 30 on the video http: //www. youtube. com/watch? v=EMa. BH 7 EKYMU

Timber rattlesnake: Crotalus horridus For an interesting video see: http: //www. youtube. com/watch? v=y 7 B 8 L 47 j. P D 0 http: //www. youtube. com/watch? v=y 7 B 8 L 47 j. PD 0

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 cell

nucleus

nucleus

nucleus

nucleus Original 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 cell

nucleus

nucleus

nucleus

nucleus

Mitosis Cell division 2 X Meiosis Cell division

meiosis sex chromosomes

X Y XY, male

X Y

X X Y Y

X X Y 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 X X Cell division 2 X XX XY X X Y Y 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 2 X ZZ ZW Z Z W W Z Z

Parthenogenesis in Vertebrates • Production of offspring from unfertilized eggs

Some Variations in Vertebrate Reproduction Ab M 1 (P 3 a. B M 2 P 2) P 4) Haplotype Homologs Parthenogenesis Gynogenesis Defective Meiosis Defective meiosis Diploid egg M 1 M 2 M 1 P 1 M 2 M 1 M 2 Diploid egg Hybridogenesis Diploid egg Fertilization M 1 M 2 P 1 P 2 P 1 or P 2 M 1 M 2 Paternal genome eliminated Defective meiosis Haploid egg (paternal genome eliminated) Diploid egg P 3 P 4 Fertilization M 1 P 3 or P 4 Development M 1 M 2 M 1 P 3 or M 1 P 4 P 3 or P 4

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 A B b Meiosis A A b B Cell division b b A A Cell division A A A A B B b b B B Cell division 2 X AA, Bb A B A b A b A B

Bonus slides – showing chromosomes with alleles

mitosis with alleles

A A b B AA, Bb

A A b b B B

A A b b B B

AA, Bb A A B b A AA, Bb b b B B

meiosis with alleles

A A B b AA, Bb

A A b B

A A b b B B

A A b b B B

A A AA, Bb B B b b A, B

A A AA, Bb b b B B A, b

Mitosis A AA, Bb Genotype of Diploid Parent Cell B A A B b Meiosis A A b B Cell division b b A A Cell division A A A A B B b b B B Cell division 2 X AA, Bb A B A b A b A B