TheMorgan is now the unit of measurement of
distances along all chromosomes in flies, mice, and
humans. The University of Kentucky honored Morgan
by naming its school of biological science after him.
morphogen Adiffusible protein molecule present in
embryonic tissues that, through a concentration gradient,
can influence the development process of a cell; different
morphogen concentrations specify different cell fates.
morphogenesis The development of body shape and
organization of an embryo from fertilized egg to adult.
morphological species concept A way to classify
organisms in the same species if they appear identical
by anatomical criteria. Recognizing a species based ini-
tially on appearance; the individuals of one species
look different from the individuals of another.
morphometrics A branch of mathematics that
focuses on the study of the metrical and statistical
properties of shapes and the changes of geometric
objects both organic or inorganic. Biologically relevant
when dealing with species that have morphs that
appear radically different.
morphotype Reference to a particular morphologi-
cal appearance of an organism or group.
mosaic development Apattern of development in
which body parts aredetermined from an early stage of
cell division; the blastomere fate is established at a very
early stage in development. Cells develop more or less
independently and are largely unaffected by each other
or the environment. When and what the cell becomes is
under tight genetic control.
mosaic evolution When different anatomical, physi-
ological, and behavioral features evolve at different
rates and at different times. Human evolution and lan-
guage are examples.
mosquitoes Anorganism belonging to the dipteran
suborder, Nematocera, the more primitive group of
flies that also includes groups such as crane flies,
midges, gnats, and black flies. This is a large, abun-
dant, and well-known family (Culicidae) whose mem-
bers are pests to humans and who, with their long
proboscises for feeding on the blood of mammals, are
vectors for disease. Aedes aegypti(L.) is a vector for
yellow fever and dengue fever, Anopheles punctipennis
(Say) is the vector for malaria, and Culex pipiens(L.) is
the vector for filariasis and encephalitis.Mössbauer effect Resonance absorption of gamma
radiation by specific nuclei arranged in a crystal
lattice in such a way that the recoil momentum is
shared by many atoms. It is the basis of a form of
spectroscopy used for studying COORDINATEDmetal
ions. The principal application in bioinorganic chem-
istry is^57 Fe. The parameters derived from the
Mössbauer spectrum (isomer shift, quadrupole split-
ting, and the HYPERFINEcoupling) provide informa-
tion about the oxidation, spin, and COORDINATION
state of the iron.moth Any of numerous insects of the order Lepi-
doptera. The nocturnal counterpart to the butterfly.
Whereas moths rest with wings in various positions,
butterflies rest with the wings folded over the back.motif A pattern of amino acids in a protein SEQUENCE
that has a specific function, e.g., metal binding.
See alsoCONSENSUS SEQUENCE.motor neuron Aneuron that sends messages from
the central nervous system (brain or spinal cord) to
smooth muscles, cardiac muscle, or skeletal muscles.
There are upper-motor neurons that lie entirely within
the central nervous system and cause movement
because they terminate on a lower motor neuron; the
lower motor neurons cell body lies in the central ner-
vous system, and their axons leave the central nervous
system through a foramen (hole in a bone for nerves
and blood vessels) and terminate on an effector (e.g.,
muscle).motor neuron 227