1. Why would the scientific method support the hypothesis of epigenesis better than the theory of preformation?

2. How can very different specialized cells have identical genes?

3. How do morphogen gradients cause cells to differentiate?

4. How are the human male and female reproductive tracts similar? How are the structures of the testis and ovary similar?

5. Arrange these prenatal humans in order from youngest to oldest: morula, gastrula, zygote, fetus, blastocyst, and embryo.

6. What events must take place for fertilization to occur?

7. What is the difference between life span and life expectancy?

1. Describe an experiment in a model organism that illustrates how cells lose pluripotency as they develop.

2. Why did biologists choose to develop a complete fate map for C. elegans, rather than for an organism more like humans?

3. What role do homeotic genes play in early development?

4. How do the developmental fates of a trophoblast cell and an inner cell mass cell differ? How do fates differ for cells in the ectoderm, endoderm, and mesoderm?

5. Toxins usually cause more severe medical problems if exposure occurs during the first 8 weeks of pregnancy rather than during the later weeks. Why?

6. How do less efficient enzymes that normally catalyze reactions carrying out DNA repair or free-radical scavenging contribute to aging?

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