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Human Reproduction and Development
March 3, 2004

Readings: Ch 38: p 644-649, 652-653, 666-673, CD-ROM: Great illustrations and quiz!

"One of life's great dramas: the development of an offspring in the image of its parents"
- Cecie Starr
I. What's the use of Sexual Reproduction?
Sexual reproduction: a costly process
  * Special reproductive cells and structures must be constructed
  * Courtship behavior, hormones, colors, scents must be developed
  * Reproductive timing � finding and recognizing mates, sperm and egg available at the same time - must occur
  * The developing embryo and young must be cared for, often for years or decades!
Why bother, then?
The genetic diversity that results from sexual reproduction increases the possibility that the offpsring will survive and pass its genes on to the next generation, offsetting the biological "cost".

II. Stages of Development of an Animal Embryo: (please know the terms mentioned in the Learning Objectives!)
How does a one-celled zygote - the product of fertilization - become a multicellular organisms with tissues, organs, and other specialized cells and structures? [Besides Lots and Lots of mitosis!]?

Most animals, including humans, go through 6 stages of embryonic development: Successful development at each stage depends on successful completion of the stage before!
1. Gamete formation (n + n): eggs and sperm are produced in specialized tissues (We already discussed Meiosis!)
2. Fertilization: the union of egg and sperm
-Occurs in Fallopian Tubes (usually)
- 200 million sperm to one egg! (sometimes 2, 3 or more eggs!).

-When 1 sperm penetrates the zona pellucida (clear zone around egg), cortical granules are released that prevent any other sperm from penetrating the egg

- After fertilization, the egg and sperm and nuclei fuse, and a new diploid human zygote results (2n) - the first cell of the new animal... |
The Moment of Fertilization |
3. Cleavage: The first days and weeks after...

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