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 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)

Hap

loty

pe

Hap

loty

peHomologs

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