Section 2

Gene Expression in Development and Cell Division

• The development of specialized cells is called cell differentiation. The development of form in an organism is called morphogenesis. Both cell differentiation and morphogenesis are governed by gene expression.

• Homeotic genes are regulatory genes that determine where anatomical structures will be placed during development.

• Within each homeotic gene, a specific DNA sequence known as the homeobox regulates patterns of development. The homeoboxes of many eukaryotic organisms appear to be very similar.

Vocabulary cell differentiation (p. 223) homeotic gene (p. 223) homeobox (p. 224) proto-oncogene (p. 225)

• Mutations of proto-oncogenes or tumor-suppressor genes may lead to cancer. Cancer is the uncontrolled growth of abnormal cells.

• A carcinogen is any substance that can induce or promote cancer. Most carcinogens are mutagens, substances that cause mutations.

• Unlike normal cells, cancer cells continue to divide indefinitely, even if they become densely packed. Cancer cells will also continue dividing even if they are no longer attached to other cells.

tumor-suppressor gene (p. 225) metastasis (p. 226) carcinogen (p. 226)

carcinoma (p. 228) sarcoma (p. 228) lymphoma (p. 228) leukemia (p. 228)

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