Sexual Reproduction

Overview of Sexual Reproduction• 2 haploid sex cells (Sperm and Egg)

combine to form new diploid organism

*Sex cells produced via meiosis*

n n

2n Fertilized Egg (Zygote)

Egg CellSperm Cell

Why Study Sea Urchins?• Eggs and sperm are the same size as in

humans

• Fertilization in sea urchins happens outside their bodies - We can watch it happen!

How Do Sea Urchins Reproduce?

• Sea urchins expel gametes (eggs and sperm) outside their bodies

• We can make this happen in the lab

• We can then watch fertilization under a microscope

Life of a Zygote

• Zygote goes through series of cell divisions via mitosis

• Also has a larval stage before it reaches adulthood

Spawning

• Inject urchins with KCl to release eggs and sperm

Spawning

• Inject urchins with KCl to release eggs and sperm

Male or Female?

Eggs are orange

Sperm are white

Collecting the Gametes

Pipette sperm from urchin to tube

Collecting the Gametes

Let eggs fall into beaker of sea water

Add Eggs and Sperm to a Slide and Observe Fertilization!

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Previously fertilized cells show additional stages of cell

development…

…as well as larval development

Some of the preceding pictures, animations, and movies are from the

following websites:

• http://www.stanford.edu/group/Urchin/ani-plus.htm

• http://www.bio.davidson.edu/misc/movies/spermrace.mov