O "O" is a program for converting x-ray crystallographic
data into 3D molecular coordinates object oriented observed heterozygosity heterogygosity 3-OH terminus The end of a polynucleotide that terminates with a
hydroxyl group attached to the 3' carbon of the sugar. Okazaki fragment one of the short segments of the RNA-primed DNA
synthesized during replication of the lagging strand of the
double helix oligonucleotide-directed mutagenesis An in vitro mutagenesis technique in which a
synthetic oligonucleotide is used to introduce a
predetermined nucleotide alteration in th the gene to be
mutated. O-linked glycosylation The attachment of sugar untis to a serine or threonine in
a polypeptide oncogene A gene that acts to promote the development of cancer,
when active. Many oncogenes are involved, directly or
indirectly, in controlling the rate of cell growth. ontogeny the sequence of events in the development of an organism
from zygote to adult. Open promoter complex A structure formed during assembly of the transcription
initiation complex consisting of the RNA polymerase and/or
accessory proteins attached to the promoter, after the DNA
has been opened up by breakage of base pairs. open reading frame (ORF) A substring in DNA that contains no stop codons (UAA,
UAG, or UGA) when read in a single reading frame.
Alternatively it is defined as a substring in DNA between
the start codon AUG and the first stop codon found in the
same reading frame as the start codon. Identifying the open
reading frams is often the first step in trying to locate
genes in a genome. operational taxonomic unit (OTU) One of the organisms being compared in a phylogenetic
analysis operator the nucleotide sequence to which a repressor protein
binds to prevent transcription of a gene or operon operon A genetic unit or cluster that consists of one or more
genes that are transcribed as a unit and expressed in a
coordinated manner optical mapping A technique for the direct visual examination of
restricted DNA molecules optimal alignment The best possible alignment of two sequences under
specific conditions. Optimal alignments are sensitive to the
scoring system, penalties for gaps, and to the algorithm
(local or global) used organelle functional membrane-enclosed structures within eukaryotic
cells (e.g., nuclei, mitochondria, chloroplasts). In common
usage, nuclei are not considered an organelle. origin of replication A site on a DNA molecule where replication initiates orphan family A group of homologous genes whose functions are
unknown orthologous Refers to homologous genes located in the genomes of
different organisms. orthologs Homologous sequences are said to be orthologous when they
are direct descendants of a sequenc ein the common ancestor
(i.e., withouth having undergone a gene duplication
event). orthology sequence similarity as a consequence of a speciation
event outgroup A species or a set of species that is the least related
to the others in a group of species. The taxon that diverged
from a group of taxa before the others diverged from each
other. out of africa A hypothesis that holds that modern humans eveolved in
Africa, moving to the rest of the Old World between 100,000
and 50,000 years ago, displacing descendants of Homo
erectus that they encountered. out-of-phase overlapping the encoding of two or more proteins in different frames
of the same DNA sequence overdominance A selection regime resulting from the heterozygote having
a higher fitness than either homozygote. overlapping genes Two genes whose coding regions overlap. overlaps Segments of sequence that are common to sequences derived
from separate sequencing experiments.