The age of development of secondary sexual characteristics varies greatly. As indicated in Chapter 16, The Breast, development of the breasts in girls may begin as early as 8 years of age and continues for the next 5 years. The development of pubic hair in girls occurs at around the same time. Testicular development in boys begins somewhat later, at about 9 to 10 years of age. Pubic hair starts to develop in boys at about 12 years of age and continues to develop until 15 years of age. The growth of the penis begins about a year after the beginning of testicular enlargement, at 10 to 11 years of age. In boys with Klinefelter syndrome (karyotype 47,XXY), this normal relationship between appearance of pubic hair, development of testes, and growth of the penis is disturbed; the hallmark of this syndrome is the presence of prepuberty-sized testes with normal pubic hair and penile length growth. Whereas the growth spurt in girls occurs at about 12 years of age, early in their pubertal development, this spurt is not seen until around 14 years of age in boys, when the genital changes are fairly well advanced.
Sex maturity ratings for boys and girls were established by J. M. Tanner in 1962. In the boy, the growth of pubic hair and the development of the penis, testes, and scrotum are used to assign a sex maturity rating from 1 to 5. The examiner should record two ratings: one for the pubic hair and one for the genitalia. If the development of the penis differs from that of the testes and scrotum, the two ratings should be averaged. The Tanner sex maturity ratings for genital development in boys are illustrated and summarized in Figure 24-44.
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