Webster's New World Medical Dictionary

2
In genetics,
the Y chromosome.
Y chromosome
The sex chromosome that is
found, together with an X chromosome, in most
normal males. The Y chromosome contains the
unique male-determining gene and the male fitness
genes that are active only in the testis and are
responsible for the formation of sperm. Other genes
on the Y chromosome have counterparts on the X
chromosome, are active in many body tissues, and
play crucial “housekeeping” roles with the cell.
Y chromosome sex-determining region
The
region on the Y chromosome that decides the sex of
the individual. Abbreviated SRY. SRY is necessary for
male determination. It encodes the testis-determin-
ing factor. Mutations in SRY are responsible for XY
females with gonadal dysgenesis who appear to be
normal females at birth but at puberty do not
develop secondary sexual characteristics (such as
breasts), do not menstruate, and have scarred
(fibrous) gonads without eggs.
Y map
The array of genes on the Y chromosome.
yard
A measurement of length that is equal to 0.9
meters, 3 feet, or 36 inches.
yawn
Involuntary opening of the mouth, accom-
panied by slowly breathing inward and then out-
ward. Repeated yawning can be a sign of
drowsiness, boredom, or depression. The yawn
helps to open tiny air sacs (alveoli) in the lungs that
can collapse during shallow breathing.
yaws
A chronic infectious disease that occurs
commonly in the warm, humid regions of the trop-
ics. Yaws is characterized by bumps on the skin of
the face, hands, feet, and genital area. Almost all
cases of yaws are in children under 15 years of age.
The organism that causes yaws is a type of spiro-
chete bacteria, Treponema pertenue, which enters
the skin at a scraped or cut spot after contact with
an infected person. A painless bump (the mother
yaw) arises and grows at this spot. Nearby lymph
nodes may become swollen. The mother yaw is fol-
lowed by recurring (secondary) crops of bumps
and more swollen lymph nodes. In its late (tertiary)
stage, yaws can destroy and deform areas of the
skin, bones, and joints. The palms and soles tend to
become thickened and painful (“dry crab yaws”).
Diagnosis is confirmed via blood tests and via 
dark-field examination of the spirochete under a
microscope. Treatment involves administration of
antibiotics. Also known as granuloma tropicum,
polypapilloma tropicum, and thymiosis.