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THE PRINCIPLES OF HEREDITY 



this bird grows into something looking exactly like a rooster. It will 

 even crow and try to mate with females. The source of the female sex 

 hormone was removed when the ovary was taken out and the engrafted 

 testes produced the male hormone. This caused suppression of the 

 female genes and expression of the male genes. If testes are engrafted 

 into young female chicks without removal of the ovaries there will 

 develop a peculiar combination of characteristics of both sexes because 

 of the influence of both hormones. There has even been one recent 



Fig. 32.9. Sex determination in human beings. All persons carry 48 chromosomes in 

 their body cells. These include two X-chromosomes in a woman and an X and a Y in 

 a man. When gametes are formed the eggs all carry an X-chromosome, while half 

 the sperm carry X-chromosomes and half carry Y-chromosomes. Sex is determined 

 by the type of sperm that fertilizes the egg. 



