Sexual differentiation and normal subsequent development are fundamental to the continuation of the human species. In recent years, our understanding of the control of this process has greatly increased. Following fertilization, the human embryo will differentiate into a male or female fetus, and subsequent development is genetically controlled. This chapter describes the processes involved and discusses the subsequent evolution to full maturation. | Chapter 3 Normal and abnormal sexual development and puberty Sexual differentiation Genetic sex Abnormal development 21 Puberty 26 21 Common clinical presentations 22 and problems 27 Sexual differentiation and normal subsequent development are fundamental to the continuation of the human species. In recent years our understanding of the control of this process has greatly increased. Following fertilization the human embryo will differentiate into a male or female fetus and subsequent development is genetically controlled. This chapter describes the processes involved and discusses the subsequent evolution to full maturation. Sexual differentiation Genetic sex The means by which the embryo differentiates is controlled by the sex chromosomes. This is known as fenetic sex. The normal chromosome complement is 46 including 22 autosomes derived from each parent. An embryo that contains 46 chromosomes and. has sex chromosomes XY will develop as a mate. Ifthe M chromosomes are XX the embryo will differenti-Jie into a female. The resulting development of the gonad will create either a teslis or an ovary. This is known as gonaclal sex. Subsequent development of e internal and external genitalia gives phenotypic A-. i r the sex ol appearance. Cerebral differen- arion to a male or female orientation is known as brain sex. hi the developing embryo with a genetic complement of 46 XY it is the presence of the Y chromosome that determines that the undifferentiated gonadwill become a testis Fig. . Absence ofthe Y chromosome will result in the development of an ovary. On the short arm of the Y chromosome is a region known as the SRI gene which is responsible for the determination oftes-ticular development as it produces a protein known as testicular determining factor TDF . TDF dircc influences the undifferentiated gonad to become testis. When this process occurs the testis abt - . . . Miillerian inhibitor. The imdifferentiated embryo contains b and Miillerian ducts. The .
