# genus

In biology, genus is a taxonomic category
ranking below family and above species.
A genus is a group of closely related biological species with common
characteristics; for example the genus *Canis* includes the dog,
wolf, and jackal. Genus names are printed in italic with a capital letter;
for example, modern humans belong to the genus *Homo*. Plural:
genera.

In topology, genus, roughly speaking, is the number of holes in a surface. Spheres, bowling balls and wine glasses have a genus of 0 and can be represented by quadratic equations. Bagels, inner tubes, and teacups have a genus of 1 and can be described by cubic equations. Humans are more difficult to specify. However, you will certainly increase your genus by one if you have your ear pierced! Different definitions of genus apply to other types of mathematical object such as a curve, a knot, or a set.