Natural and Experimental Sex Reversal in Birds and Other Groups of Vertebrates, with the Exception of Mammals

The review is focused on the current problem of sex determination. Many research papers were devoted to this issue, but all the details of its mechanisms have not yet been disclosed, since they are very diverse. The article summarizes new data obtained in the studies of natural and experimental sex reversal cases in vertebrates. Representatives of cold-blooded (fish, amphibians, reptiles) and warm-blooded (birds) vertebrates are considered. Sex reversal, which occurs in both natural and experimental conditions, may result from genetic disorders that appear at the early stages of embryonic development, as well as from normal changes that occur in mature animals under the control of neuroendocrine system. It is suggested that sex reversal and sex determination can be interrelated phenomena. Special emphasis is put on sex reversal and determination in birds. The studies on experimental sex reversal in these animals are considered in detail. For these purposes, the results of research studies on the relationship between the phenotypic sex manifestation at the cellular, tissue, and organ levels and its chromosomal and hormonal determination, as well as genetic and epigenetic control, are summarized. Finally, promising directions in the study of natural and experimental sex reversal in vertebrates are suggested.