This edition: Generations: Mitosis and Meiosis
Cell division is at the heart of all the stories in the program. They illustrate how this process powers a continuous stream of molecular messages that define each organism and how it grows, reproduces, and repairs itself. Dr. Christopher Wills and Dr. Gary Karpen explain how hereditary instructions contained in chromosomes dictate the physical and behavioral traits of organisms. For continuance, each species must pass on those instructions from one generation to the next.
The program reveals that each species has a specific number of chromosomes: Humans have 46, horsetail grass has 216, and pea plants have 14. As an organism develops, its cells begin to differentiate into various forms (e.g., nerve cells, muscle cells, and bone cells) that are not clones, although each cell in an organism does carry an exact copy of all chromosomes. The process of mitosis is illustrated by a trip to a winery, where grapes of prime stock are cloned to preserve genetic characteristics in each crop.
In contrast, meiosis produces cells, called gametes, with only half of the hereditary information of the parent germ cells. Researcher Arlene Kumamoto of the Center for Reproduction of Endangered Species discusses the implication of cell division on the reproductive patterns of dik-dik antelopes at the San Diego Zoo.