in boys following changes occur 
Pubic hair growth -- as well as armpit, leg, chest, and facial hair -- begins in boys at about age 12, and reaches adult patterns at about 15 to 16 years. 
Boys do not start puberty with a sudden incident, like the beginning of menstrual periods 
Boys' voices change at the same time . Nocturnal emissions occur with the peak of the height spurt. 

and in girls following changes occur 
Pubic hair, armpit and leg hair usually begin to grow at about age 9 or 10, and reach adult patterns at about 13 to 14 years. 
Menarche occurs about 2 years after pubic hair appear. It may occur as early as age 10, or as late as age 15. 
Girls have a rapid growth in height between ages 9.and 14., peaking at around age 12. 
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The following changes occur during adolescence period
1) the male hormone begins to be released by the testes.the testes and penis become larger . the testes start making sperms.
2) IN GIRLS - the ovaries start producing the female hormone. as a result the ovaries enlarge and start releasing the egg.
3) HEIGHT INCREASE- there is a sudden increase in height during adolescence . in both boys and girls.
4) CHANGES IN BODY SHAPE- in boys shoulder becomes broader and the chest becomes wider. 
5) HAIR DEVELOPMENT- in both boys and girls hair starts growing in the armpits and in the pubic area. 
6)VOICE CHANGES- boys develop a deep voice 

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