|
narrow-sense heritability:
The proportion of the phenotypic variance that results from additive
genetic variance.
nasal root: The top
of the nose, the indentation at the suture where the nasal bones
meet the frontal bone.
nasal spine (anterior):
The thin projection of bone at the midline on the lower nasal margin,
holding the cartilaginous center of the nose.
nasion: The point on
the midline where the two nasal bones and the frontal come together.
nasoalveolar clivus:
Portion of the premaxilla extending from the nasal cavity to the
incisor root sockets.
nasofrontal suture:
The suture along the upper border of the nasal bones with the frontal.
Its shape can help determine geograohic origin.
nasolacrimal duct:
See lacrimal duct.
nasospinale: Midpoint
of the lower nasal aperture.
natural selection:
Difference in reproductive success and/or survivorship of individuals
that result in the unequal contribution of genotypes to the gene
pool of the next generation.
neck: A constricted
portion of a bone immediately below the "head".
negative assortative
mating: A mating that occurs between dissimilar individuals more
often than it does between randomly chosen individuals.
negative feedback:
In systems thinking, this is a process which acts to counter or
"dampen" the potentially disruptive effects of external
inputs; it acts as a stabilizing mechanism.
neocortex: The cortex,
or outer surface of the cerebral hemispheres of the brain.
Neogene: A part of
the Cenozoic including the Miocene and Pliocene.
Neolithic: An Old World
chronological period characterized by the development of agriculture
and, hence, an increasing emphasis on sedentism.
Neolithic Revolution:
A term coined by V.G. Childe in 1941 to describe the origin and
consequences of farming (i.e. the development of stock raising and
agriculture), allowing the widespread development of settled village
life.
neolocal: Residence
of a couple after marriage in a new household not linked spatially
to that of the groom's or the bride's kin (cf. virilocal, uxorilocal).
neonate: A newborn
infacnt.
neural: Pertaining
to a nerve or the nervous system.
neural canal: The large
opening though the vertebrae than encloses the spinal cord, also
called the vertebral canal.
neurocranium: The portion
of the skull enclosing the brain, as distinct from the facial bones
and the basicranium.
neuron: Nerve cell.
neutral evolution:
Genetic changes that do not affect the fitness of the individual
or its offspring.
neutral mutation: A
base-pair change in the gene that changes a codon in the mRNA so
that there is no change in the function of the protein translated
from that message.
neutral-mutation hypothesis:
A hypothesis that replaced the classical model by acknoledging the
presence of extensive genetic variation in proteins, but proposing
that this variation is neutral with regard to natural selection.
neutron activation
analysis (NAA): A method used in the analaysis of artifact composition
which depends on the excitation of the nuclei of the atoms of a
sample's various elements, when these are bombarded with slow neutrons.
The method is accurate to about plus or minus 5 percent.
New Archaeology: A
new approach advocated in the 1960s which argued for an explicitly
scientific framework of archaeological method and theory, with hypotheses
rigorously tested, as the proper basis for explanation rather than
simply description.
New World primate:
A primate from North or South America.
niche: The limited
portions of the environment, in terms of space, resources, etc.,
that a species fits and/or that it requires for its survival and
reproductive success.
NISP (number of identified
specimens): A gross counting technique used in the quantification
of animal bones. The method may rpoduce misleading results in assessing
the relative abundance of different species, since skeletal differences
and differential rates of bone preservation mean that some species
will be represented more than others.
nitrogenous base: A
nitrogen-containing base that, along with a pentose sugar and a
phosphate, is one of the three parts of a nucleotide, the building
block of RNA and DNA.
nocturnal: Primarily
active during the night.
noncontributing alleles:
The alleles that do not have any effect on the phenotype of the
quantitative trait.
nondisjunction (primary
disjunction): A failure of homologous chromosomes or sister chromatids
to separate at anaphase.
nonhistone: A type
of acidic or neutral protein found in a chromatin.
nonhomologous chromosomes:
The chromosome containing dissimilar genes that do not pair during
meiosis.
non-Mendelian inheritance
(cytoplasmic inheritance): The inheritance of characters determined
by genes not located on the nuclear chromosomes but on mitochondrial
or chloroplast chromosomes. Such genes show inheritance patterns
distinctively different from those of nuclear genes.
nonmetric trait: Feature
whose expression is better or more accurately described as discrete
charater states than as measurements.
nonparental-ditype
(NPD): One of three types of tetrads possible when two genes are
segregating in a cross. The NPD tetrad contains four nuclei, all
of which have recombinant (non-parental) genotypes, that is, two
of each possible type.
non-probabilistic sampling:
A statistical sampling strategy which concentrates on sampling areas
on the basis of intuition, historical documentation, or long field
experience in the area.
nonsense codon: See
chain-terminating codon.
nonsense mutation:
A gene mutation in which a base-pair change in the DNA causes a
change in an mRNA codon from an amino acid-coding codon to a chain-terminating
(nonsense) codon. As a result, polypeptide chain synthesis is terminated
prematurely and is therefore either nonfunctional or, at best, partially
functional.
nontranscribed spacer
(NTS) sequence: Sequences, which are not transcribed, found between
transcription units in rDNA. Important sequences that control transcription
of the rDNA are within the NTS.
non-unilineal descent:
An alternative term to cognatic descent. Since cognatic descendants
include patrilineal descendants and matrilineal descendants this
usage is flawed. It has been suggested that the term be used in
societies that recognize a unilineal core within a cognatic descent
category to denot descent status through at least one alternate
sex link (i.e., non-agnatic where descent includes at least one
female link, nonuterine where it includes at least one male link).
normal distribution:
A probability distribution in statistics, graphically displayed
as a bell-shaped curve.
normal polarity epoch:
Period of geological time in which the earth's magnetic field is
directed as it is at present.
norm of reaction: The
extent to which the phenotype produced by a genotype varies with
the environment.
northern blot analysis:
A similar technique to Southern blotting except that RNA rather
than DNA is separated and transferred to a filter for hybridization
with a probe.
nuchal: Pertaining
to the nape of the neck.
nuchal crest: A raised
bony ridge on the back of the skull caused by the attachment of
neck muscles.
nuchal line: Three
lines that transversely cross the cranial rear. From lowest to highest
they are:
inferior nuchal line extends across the middle of the nuchal lane,
separating the nuchal muscles semispinalis capitis above from rectus
capitis below.
superior nuchal line
the most prominent, develops along the top of the semispinalis capitis
muscle and some of the muscles lying over it attach directly to
the line, trapezius more centrally and sternocleidomastoid more
laterally. It separates the nuchal from the occipital planes of
the occiput.
supreme nuchal line
lies above the superior line, on the occipital plane. It may be
totally absent, a distinct line dipping downward at the midline,
or the superior border of the nuchal torus (if there is one).
nuchal plane (lower scale): The area at the nape of the neck where
the neck muscles attach, the lower portion of the occipital bone
below the superior nuchal line.
nuchal torus: A thickened
bony prominence extending transversely across some or all of the
back of the head, on the occipital bone, reflecting the pattern
of muscle use as it separates the nuchal plane below from the occipital
plane above.
nuclear family: A family
unit consisting of parents and their dependent children.
nuclease: An enzyme
that catalyzes the degradation of a nucleic acid by breaking phosphodiester
bonds. Nucleases specific for DNA are termed deoxyribonucleases
(DNases), and nucleases specific for RNA are termed ribonucleases
(RNases).
nucleofilament: A fiber
seen in chromatin. It is approximately 10 nm in diameter and consists
of DNA wrapped around nucleosome cores.
nucleoid: Central region
in a bacterial cell in which the chromosome is compacted.
nucleolus: An organelle
within the eukaryotic nucleus; the site of transcription of the
ribosomal RNA genes and assembly of the ribosomal subunits.
nucleoside phosphate:
See nucleotide.
nucleosome: The basic
structural unit of eukaryotic nuclear chromosomes, consisting of
two molecules each of the four core histones (H2A, H2B, H3, and
H4, the histone octamer), a single molecule of the linker histone
H1, and about 180 bp of DNA.
nucleotide: A monomeric
molecule of RNA and DNA that consists of three distinct parts: a
pentose (ribose in RNA, deoxyribose in DNA), a nitrogenous base,
and a phosphate group.
nucleus: A discrete
structure within the cell that is bounded by a nuclear membrane.
It contains most of the genetic material of the cell.
nullisomy: The aberrant,
aneuploid state in a normally diploid cell or organism in which
there is a loss of one pair of homologous chromosomes.
numerical dating: Age
estimation in calendrical years before the present, also known as
absolute dating, chronometric dating.
nutritional mutation:
See auxotraphic mutation.
|
