A chromosomal segment that branches off from the rest of the
chromosome but is still connected by a thin filament or stalk.
(ORNL)
Scaffold
In genomic mapping, a series of contigs that are in the right
order but not necessarily connected in one continuous stretch
of sequence. (ORNL)
Seed Alignment
Alignment that contains only one of each pair of homologues
that are represented in a CLUSTALW-derived phylogenetic tree
linked by a branch of length less than a distance of 0.2 (see
the related article). (SMART)
A program for filtering low complexity regions in amino acid
sequences. Residues that have been masked are represented as
"X" in an alignment. SEG filtering is performed by
default in the blastp subroutine of BLAST 2.0. (Wootton and
Federhen) (NCBI)
Segregation
The normal biological process whereby the two pieces of a
chromosome pair are separated during meiosis and randomly distributed
to the germ cells. (ORNL)
Short (200 to 500 base pairs) DNA sequence that has a single
occurrence in the human genome and whose location and base sequence
are known. Detectable by polymerase chain reaction, STSs are
useful for localizing and orienting the mapping and sequence
data reported from many different laboratories and serve as
landmarks on the developing physical map of the human genome.
Expressed sequence tags (ESTs) are STSs derived from cDNAs.
(ORNL)
The X or Y chromosome in human beings that determines the
sex of an individual. Females have two X chromosomes in diploid
cells; males have an X and a Y chromosome. The sex chromosomes
comprise the 23rd chromosome pair in a karyotype.
See also: autosome (ORNL)
Sequencing method that involves randomly sequenced cloned
pieces of the genome, with no foreknowledge of where the piece
originally came from. This can be contrasted with "directed"
strategies, in which pieces of DNA from known chromosomal
locations are sequenced. Because there are advantages to both
strategies, researchers use both random (or shotgun) and directed
strategies in combination to sequence the human genome.
See also: library, genomic
library (ORNL)
Similarity
The extent to which nucleotide or protein sequences are related.
The extent of similarity between two sequences can be based
on percent sequence identity and/or conservation. In BLAST similarity
refers to a positive matrix score. (NCBI)
Single nucleotide polymorphism (SNP)
DNA sequence variations that occur when a single nucleotide
(A, T, C, or G) in the genome sequence is altered.
See also: mutation, polymorphism,
single-gene disorder
(ORNL)
Hereditary disorder caused by a mutant allele of a single
gene (e.g., Duchenne muscular dystrophy, retinoblastoma, sickle
cell disease).
See also: polygenic disorders
(ORNL)
Somatic cell
Any cell in the body except gametes and their precursors.
See also: gamete (ORNL)
Incorporating new genetic material into cells for therapeutic
purposes. The new genetic material cannot be passed to offspring.
See also: gene therapy (ORNL)
Somatic cell
genetic mutation
A change in the genetic structure that is neither inherited
nor passed to offspring. Also called acquired mutations.
See also: germ line
genetic mutation (ORNL)
Southern
blotting
Transfer by absorption of DNA fragments separated in electrophoretic
gels to membrane filters for detection of specific base sequences
by radio-labeled complementary probes. (ORNL)
Spectral karyotype (SKY)
A graphic of all an organism's chromosomes, each labeled with
a different color. Useful for identifying chromosomal abnormalities.
See also: chromosome (ORNL)
Splice site
Location in the DNA sequence where RNA removes the noncoding
areas to form a continuous gene transcript for translation into
a protein. (ORNL)
Cancer that occurs randomly and is not inherited from parents.
Caused by DNA changes in one cell that grows and divides,
spreading throughout the body.
See also: hereditary cancer
(ORNL)
Stem cell
Undifferentiated, primitive cells in the bone marrow that
have the ability both to multiply and to differentiate into
specific blood cells. (ORNL)
Structural genomics
The effort to determine the 3D structures of large numbers
of proteins using both experimental techniques and computer
simulation (ORNL)
Substitution
The presence of a non-identical amino acid at a given position
in an alignment. If the aligned residues have similar physico-chemical
properties the substitution is said to be "conservative".
(NCBI)
Substitution
In genetics, a type of mutation due to replacement of one
nucleotide in a DNA sequence by another nucleotide or replacement
of one amino acid in a protein by another amino acid.
See also: mutation (ORNL)
Substitution Matrix
A substitution matrix containing values proportional to the
probability that amino acid i mutates into amino acid j for
all pairs of amino acids. such matrices are constructed by assembling
a large and diverse sample of verified pairwise alignments of
amino acids. If the sample is large enough to be statistically
significant, the resulting matrices should reflect the true
probabilities of mutations occuring through a period of evolution.
(NCBI)
Suppressor gene
A gene that can suppress the action of another gene. (ORNL)
