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

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 Professor Chiszar’s Big Surprise snakes

For a nice photo, see: Timber rattlesnake Crotalus horridus

For a nice video see The newborn snake pops out at about 2:30 on the video Timber rattlesnake: Crotalus horridus

For an interesting video see: D0 Timber rattlesnake: Crotalus horridus

Professor Chiszar’s big surprise For an nice photo see: oviviparity

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)

cell nucleus

Daughter nucleus Daughter nucleus Original nucleus

Could the baby snake be produced by mitosis?

For a nice photo of fertilization, see conception Well, where do baby snakes usually come from?

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

cell nucleus

MeiosisMitosis 2X Cell division

meiosis sex chromosomes

XY, male XX YY

XX YY

XXXX YYYY

XXXX YYYY

XX XX YY YY X Y X X Y Y

Meiosis Mitosis 2X Cell division X YXYYXXXXX XX YY X Y XX XXXX YY XX X X Y Genetic Sex Determination In Mammals

Meiosis Mitosis 2X Cell division Z WZWWZZZZZ ZZ WW Z W ZZ ZZZZ WW ZZ Z Z W Genetic Sex Determination In Birds,Reptiles

Parthenogenesis in Vertebrates Production of offspring from unfertilized eggs

A b a B M1 M2 (P1 P2) (P3 P4) Haplotype Homologs Some Variations in Vertebrate Reproduction ParthenogenesisGynogenesis M1 M2 Defective meiosis M1 M2 Diploid egg M1 M2 Development Diploid egg M1 M2 M1 M2 M1 M2 P1 or P2 M1 M2 Paternal genome eliminated Defective Meiosis Fertilization Development M1 M2 P1 P2 Hybridogenesis Defective meiosis M1 P1 M1 or M1 P4 P3 or P4 M1 P3 or P4 M1 P3 or P4 Fertilization Development P3 P4 M1 P3 Haploid egg (paternal genome eliminated) Diploid egg

Parthenogenesis in Vertebrates Where might meiosis “go wrong” so that a diploid egg cell is produced?

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

AAAA bbBB AA, Bb

AAAAAAAA bbbbBBBB

AAAA AAAA bbbb BBBB

AA AA bb BB AA AA bb BB AAAA BBbb

meiosis with alleles

AAAA BBbb AA, Bb

AAAA bbBB

AAAAAAAA bbbbBBBB

AAAAAAAA bbbb BBBB

AA AA bbbb AAAA BB BB A, b A, B AA, Bb

AA AA BBBB AAAA bb bb A, B A, b

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