Answer the following question given this paragraph: 

The majority of human genes have two or more possible alleles , which are alternative forms of a gene. Differences in alleles account for the considerable genetic variation among people. In fact, most human genetic variation is the result of differences in individual DNA bases within alleles.


Q: The structure of the human tail bone is called what?

 Choices:

- a abnormal structure

- a vital structure

- an artifact

- a vestigial structure

A:
a vestigial structure
