A Y-DNA test, also known as a paternal lineage test, looks at the Y chromosome.
The Y chromosome is one of two sex chromosomes, X and Y. Sex chromosomes carry the genetic code that makes each of us biologically female or male.
Typically, people inherit two sex chromosomes. One comes from their mother and the other from their father.
Mothers always pass down an X chromosome to their children (both male and female). However, Fathers can pass down either an X chromosome or a Y chromosome, which determines the biological sex of the child.
When a father passes on a Y chromosome, the child is biologically male because they have a mixed set of chromosomes, XY: the X chromosome from their mother and a Y chromosome from their father.
When the father passes on an X chromosome, the child is biologically female because they have a pair of X chromosomes: one X chromosome from their mother and one X chromosome from their father.
Therefore, since females do not inherit a Y chromosome, they can not take a Y-DNA (paternal lineage) test.