<P> The Y chromosome is one of two sex chromosomes ( allosomes ) in mammals , including humans , and many other animals . The other is the X chromosome . Y is the sex - determining chromosome in many species , since it is the presence or absence of Y that determines the male or female sex of offspring produced in sexual reproduction . In mammals , the Y chromosome contains the gene SRY , which triggers testis development . The DNA in the human Y chromosome is composed of about 59 million base pairs . The Y chromosome is passed only from father to son . With a 30 % difference between humans and chimpanzees , the Y chromosome is one of the fastest - evolving parts of the human genome . To date , over 200 Y - linked genes have been identified . All Y - linked genes are expressed and ( apart from duplicated genes ) hemizygous ( present on only one chromosome ) except in the cases of aneuploidy such as XYY syndrome or XXYY syndrome . ( See Y linkage . ) </P>
<P> The Y chromosome is one of two sex chromosomes ( allosomes ) in mammals , including humans , and many other animals . The other is the X chromosome . Y is the sex - determining chromosome in many species , since it is the presence or absence of Y that determines the male or female sex of offspring produced in sexual reproduction . In mammals , the Y chromosome contains the gene SRY , which triggers testis development . The DNA in the human Y chromosome is composed of about 59 million base pairs . The Y chromosome is passed only from father to son . With a 30 % difference between humans and chimpanzees , the Y chromosome is one of the fastest - evolving parts of the human genome . To date , over 200 Y - linked genes have been identified . All Y - linked genes are expressed and ( apart from duplicated genes ) hemizygous ( present on only one chromosome ) except in the cases of aneuploidy such as XYY syndrome or XXYY syndrome . ( See Y linkage . ) </P>
a gene on the y chromosome that determines maleness is
a gene on the y chromosome that determines maleness is
SRY
SRY