SAMPLE ESSAY WITH PARENTHETICAL CITATION
SEX CHROMOSOMES
The sex chromosomes were first described by American geneticist Thomas Hunt Morgan
in 1906. His experiments involved the observation of the chromosomes in the sex organs
of fruit flies. He noted that in male fruit flies not every chromosome had a homologous
pair (Ritter 554), that is, two chromosomes alike in size, shape and banding pattern of
genes (Kelly 10). He observed that the last pair of chromosomes in females had the same
size and shape (ie. they were homologous), but the last pair in males didn’t. One of the
chromosomes was smaller and had a hooked shape. The small chromosome was called Y
and the larger one X. Morgan called this odd pair in males the sex chromosomes and
observed that the female sex chromosomes were homologous (Ritter 555).
Human females have two X chromosomes while males have one X and one Y
chromosome; thus, the presence of the Y chromosome indicates maleness (Ritter 555).
Current theory identifies one gene on the Y chromosome as being responsible for
maleness. It is called SRY for “sex determining region Y” (Jegalian 57). A full
explanation of the differences between the X and Y chromosomes continues to be
researched.
Works Cited for the above example (this should appear on a separate page of your
paper, list alphabetically, note indents):
Works Cited
Jegalian, Karin and Lahn, Bruce. “Why the Y is so Weird”. Scientific American, Volume
284: Scientific American, Inc., February 2001.
Kelly, Thaddeus E.. Clinical Genetics and Counseling. Chicago, USA: Year Book
Medical Publishers, Inc., 1986.
Ritter, Bob and Coombs, Richard. Biology. Scarborough, Canada: Nelson Canada,
1993.
Below are copies of the references that were used to write the example: