Session One: How are living things made?

How does a fertilized egg turn into a fly, a chicken, you or me?

Think about the diversity in the world. There are different kinds of animals and people. Each is made from a single cell. How does a single cell become a living thing? The process where a single cell becomes a living thing is called DEVELOPMENT. People who study development are called developmental biologists.

Watch NOVA video of human development.

Ask: How did the single cell (created when the father's sperm fertilizes the mother's egg) know to make a human being?

Answer: The instructions are in the cell. The instructions are contained within genes. Genes are made up of DNA. So a human being becomes a human, and a dog a dog, etc. because their genes contain different instructions or blueprints.

Scientists obviously can not do experiments on humans. So instead, they try to gain a better understanding of development by studying the development of model organisms such as mice, fruit flies, or worms.

We study worms. Why?? The worm lives in the dirt; it is a soil nematode. It is small, less than 1/16 of an inch long. To study it, we have to use a microscope.

Other advantages include:

1. transparent
2. easy to handle and grow large numbers of worms
3. two sexes: hermaphrodite and male
4. small number of cells, only 959 somatic cells and approximately 1000 germ cells in the adult
5. known cell lineage (show)
   Scientists watched cells divide as the worm developed. They traced the pattern of cell divisions and discovered what each cell makes such as muscle, intestine, etc. Here is a family tree of every cell in the worm.