Hormones as a Key to Understanding Genes

All mammals start as a single-celled zygote—an egg that has been fertilized by a sperm—that undergoes a rapid sequence of mitotic divisions until it reaches the stage of a hollow, microscopic ball of identical cells called the blastula. Signaling molecules called hormones stimulate the blastula to fold in upon itself and form layers of tissue that gradually become differentiated into organs because of the presence of other hormones, which affect the tissue in sequence. Still other hormones later influence the interactions of organ systems for the smooth function of the organism. Knowledge of the chemical mechanisms and sequences through which hormones exert their effects will provide the key to understanding the action of genes, which in a more fundamental way are re sponsible for the various stages of life. Hormones direct cellular differentiation and development in the organism for the rest of its life. Hormones will be crucially involved in fetal development, birth, early growth and development, puberty, reproductive cycles, aging, and eventually death. Hormones control virtually all aspects of an organism's life.

If certain relevant mammalian developmental hormones can be identified, then target cells— cells that respond to the hormones in discrete but interrelated ways—may also be determined. A "developmental profile" for any organism would then be a real possibility, and the control of any organism's development, even behavior, could result, although this may pose ethical problems.

Currently, there is some detailed knowledge of the functions of many developmental hormones. Many hormones remain to be identified, however, and the overall scheme of hormonal control of development is still sketchy. Extensive research will be needed in the future.

—David Wason Hollar, Jr. See also: Aging; Communication; Development: Evolutionary perspective; Endocrine system of vertebrates; Estrus; Gametogenesis; Genetics; Growth; Hibernation; Lactation; Mammals; Mating; Morphogenesis; Regeneration; Reproductive system of female mammals; Reproductive system of male mammals; Rhythms and behavior.

Pregnancy And Childbirth

Pregnancy And Childbirth

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