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Introduction to the
Case of the Mysterious SnakeTo 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 showNotes 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: http://animals.timduru.org/dirlist/snake/TimberRattlesnake_01-OnSand.jpg
Timber rattlesnakeCrotalus horridus
http://animals.timduru.org/dirlist/snake/TimberRattlesnake_01-OnSand.jpg
For a nice video seehttp://www.youtube.com/watch?v=EMaBH7EKYMU The newborn snake pops out at about 2:30 on the video
Timber rattlesnake: Crotalus horridus
http://www.youtube.com/watch?v=EMaBH7EKYMU
For an interesting video see: http://www.youtube.com/watch?v=y7B8L47jPD0
Timber rattlesnake: Crotalus horridus
http://www.youtube.com/watch?v=y7B8L47jPD0
Professor Chiszar’s big surprise
For an nice photo see:
http://www.bbc.co.uk/nature/adaptations/Ovoviviparity
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)
cell
nucleus
nucleus
nucleus
nucleus
nucleus
Daughternucleus
Daughternucleus
Originalnucleus
nucleus
Could the baby snake be produced by mitosis?
For a nice photo of fertilization, see
http://www.webmd.com/baby/ss/slideshow-conception
Well, where do baby snakes usually come from?
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
cell
nucleus
nucleus
nucleus
nucleus
nucleus
nucleus nucleusnucleusnucleus
MeiosisMitosis
2X
Cell divisionCell division Cell division
Cell division Cell division
meiosissex chromosomes
XY, male
X
Y
X
Y
X X
YY
XX
Y Y
X X
Y Y
X Y
X X Y Y
MeiosisMitosis
2X
Cell division
Cell division Cell division
Cell division Cell division
X Y X Y Y X X X XX
X X
Y Y
X
Y
X X X X X XY Y
X X
X X
X Y
Genetic Sex DeterminationIn Mammals
MeiosisMitosis
2X
Cell division
Cell division Cell division
Cell division Cell division
Z W Z W W Z Z Z ZZ
Z Z
W W
Z
W
Z Z Z Z Z ZW W
Z Z
Z Z
Z W
Genetic Sex Determination
In Birds,Reptiles
Parthenogenesis in Vertebrates• Production of offspring from unfertilized eggs
A b a BM1 M2(P1 P2)(P3 P4)
Hapl
otyp
e
Hapl
otyp
eHomologs
Some Variations in Vertebrate ReproductionParthenogenesis Gynogenesis
M1 M2
Defectivemeiosis
M1 M2
Diploid egg M1 M2
Development
Diploid egg
M1 M2
M1M2
P1 or P2
M1 M2
Paternal genome
eliminated
DefectiveMeiosis Fertilization
Development
M1 M2
P1 P2
Hybridogenesis
Defective meiosis
M1 P1
M1
or M1 P4
P3 or P4
M1P3 or
P4
Fertilization
Development
P3 P4
M1 P3
Haploid egg (paternal genome
eliminated)
Diploid egg
Diploid egg
Parthenogenesis in Vertebrates
Where might meiosis “go wrong” so that a diploid egg cell is
produced?
MeiosisMitosis
2X
Cell division Cell division Cell division
Cell division Cell division
AA, Bb A B A b A b A b A b A B A BA B
Genotype ofDiploid Parent
Cell
AA, Bb
A A
B B
b b
A A
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
mitosiswith alleles
A A
b B
AA, Bb
AA A A
bb B B
A A
A A
b b
B B
A
A
b
B
A
A
b
B
A A
B b
AA, Bb
AA, Bb AA, Bb
meiosiswith alleles
A A
B b
AA, Bb
A A
b B
AA A A
bb B B
AA A A
bb B B
A A
b b
A A
B B
A, b A, b A, B A, B
AA, Bb
A A
B B
A A
b b
AA, Bb
A, B A, B A, b A, b
MeiosisMitosis
2X
Cell division Cell division Cell division
Cell division Cell division
AA, Bb A B A b A b A b A b A B A BA B
Genotype ofDiploid Parent
Cell
AA, Bb
A A
B B
b b
A A
A
B
A
b
A
B
A
B
A
b
A
b
A
b
A
B
A
b
A
B
A
B
A
b