Webster's New World Medical Dictionary

inheritance, mitochondrial
The inheritance of
a trait encoded in the mitochondrial genome.
Mitochondrial inheritance does not obey the classic
rules of genetics. Mitochondrial DNA is always
inherited from the mother only, meaning that per-
sons with a mitochondrial disease may be male or
female but are always related in the maternal line,
and no male with the disease can transmit it to his
children. The mitochondria are structures in the
cell’s cytoplasm, located outside the nucleus, and
are responsible for energy production (metabo-
lism). See also 
mitochondria; mitochondrial 
diseases.
inheritance, multifactorial
A type of hereditary
pattern seen when there is more than one genetic
factor and, sometimes, environmental influence.
Many common traits and many common diseases
are multifactorial. Skin color, for example, is multi-
factorially determined, as is intelligence. Type 2 dia-
betes is multifactorial because it is due to inherited
(genetic) factors but may also require environmen-
tal factors, such as obesity, to develop.
inheritance, Y-linked
Inheritance of genes on
the Y chromosome. Because normally only males
have Y chromosomes, Y-linked genes can be trans-
mitted only from father to son. Also known as
holandric inheritance.
inhibin
One of two hormones (designated
inhibin-A and inhibin-B) secreted by the gonads (by
Sertoli cells in the male and the granulosa cells in
the female) and that inhibit the production of folli-
cle-stimulating hormone (FSH) by the pituitary
gland. The inhibins are also involved in the control
of the production of gametes and embryonic and
fetal development. Because inhibin-A is elevated in
the blood serum of women carrying a fetus with
Down syndrome, inhibin-A is included in the mater-
nal serum screening tests for Down syndrome in the
second trimester of pregnancy.