Webster's New World Medical Dictionary

Meibomian cyst
See 
cyst, Meibomian.
Meibomian gland
See 
gland, Meibomian.
meibomianitis
Inflammation of the little glands
in the tarsus of the eyelids. Chronic inflammation of
these glands can lead to a lump in the eyelid known
as a chalazion. Also known as meibomitis.
meibomitis
See 
meibomianitis.
meiosis
The process chromosomes undertake
during germ-cell formation to halve the chromo-
some number from 46 to 23. In meiosis, the 46
chromosomes in the cell divide to make two new
cells with 23 chromosomes each. Before meiosis is
complete, however, chromosomes pair with their
corresponding chromosomes and exchange bits of
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genetic material. In women, X chromosomes pair; in
men, the X and Y chromosomes pair. After the
exchange, the chromosomes separate, and meiosis
continues.
meiotic
Pertaining to meiosis.
meiotic nondisjunction
Failure of two mem-
bers of a chromosome pair to separate from one
another during meiosis, causing both chromosomes
to go to a single daughter cell. Meiotic nondisjunc-
tion is responsible for the extra chromosome 21 in
trisomy 21 (Down syndrome) and for extra and
missing chromosomes that cause other birth defects
and many miscarriages.
melan-
Prefix meaning dark or black, as in
melancholia (a dark and gloomy mood) and
melanin (a dark pigment).
melancholia
An old term for depression.
melanin
The pigment that gives human skin, hair,
and eyes their color. Dark-skinned people have
more melanin in their skin than light-skinned peo-
ple have. Melanin is produced by cells called
melanocytes. It provides some protection again skin
damage from the sun, and the melanocytes increase
their production of melanin in response to sun
exposure. Freckles, which occur in people of all
races, are small, concentrated areas of increased
melanin production.