When a particular mutagen identified by the Ames test is...

When a particular mutagen identified by the Ames test is injected into mice, it causes the appearance of many tumors, showing that this substance is carcinogenic. When cells from these tumors are injected into other mice not exposed to the mutagen, almost all of the new mice develop tumors. However, when mice carrying mutagen-induced tumors are mated to unexposed mice, virtually all of the progeny are tumor free. Why can the tumor be transferred horizontally (by injecting cells) but not vertically (from one generation to the next)?

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Key Concepts

Germline Mutation

Germline mutations occur in the reproductive cells (sperm or ova) and can be inherited by offspring. Unlike somatic mutations, changes in these cells affect every cell in the organism, making them responsible for hereditary conditions, but they are not involved in the development of tumors induced by external mutagens in non-germ cells.

Carcinogenesis

Carcinogenesis is the process by which normal cells transform into cancerous cells due to the accumulation of mutations, typically somatic mutations. This process usually remains confined to the individual in which the mutations occur, which explains why cancer developed from such mutations can be transmitted horizontally (by transferring tumor cells) but not passed vertically to progeny.

Somatic Mutation

Somatic mutations are genetic alterations acquired by non-reproductive cells during an organism's lifetime. These mutations can lead to uncontrolled cell growth and tumor formation, but because they occur in cells that are not involved in reproduction, they are not passed on to the next generation.

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