XY is the normal chromosomal makeup of a male mammal. The mother provides the X chromosome while the father provides the Y chromosome. Combining these chromosomes creates XY. XY is the alternative to XX, the normal chromosomal makeup of a female mammal.
Usually we refer to XY chromosomes, rather than using the letters XY on their own.
More About XY
The XY chromosomes come from the parents’ sex cells. The female ovum always has the X chromosome. Sperm contain either an X or Y chromosome. When a sperm with a Y chromosome fertilizes an ovum, they form a new cell call a zygote with both the X and Y chromosomes. The zygote develops to become an embryo and later a baby.
Babies with XY chromosomes are usually assigned the male gender at birth. These chromosomes typically give them male characteristics, such as a penis and scrotum.
While XY chromosomes normally make someone a cisgender male, this isn’t always the case. For example, people with androgen insensitivity syndrome have cells that don't respond to testosterone. They have XY chromosomes and female bodies. There are also people born with XY chromosomes and ambiguous genitalia. Then there are transgender people who have a female gender identity, despite possessing the XY chromosomes that usually point to a male identity.
