25
Dec
2009
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Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

R

R
Arginine.
radical substitution
The substitution of an amino acid by another with markedly different chemical properties.
random genetic drift (drift, genetic drift)
The fluctuation in allele frequencies from generation to generation caused by chance events, such as gamete sampling.
rate of gene substitution
The number of gene substitutions per locus per unit time.
rate of mutation
The number of mutations per locus or nucleotide site per unit time, usually per generation time.
rate of nucleotide substitution
The number of nucleotide substitutions per nucleotide site per unit time.
reading frame
Linear sequence of codons in a protein-coding gene starting with the initiation codon and ending in the termination codon.
recessiveness
Lack of expression of an allele in the heterozygote.
recognition sequence
The sequence recognized by a restriction endonuclease. In many cases, a short palindrome.
recombination
The situation arising following a crossover event, in which new combinations of alleles are found in cis.
recombinator gene
A regulatory gene providing a recognition site for the recombination enzymes.
reduction division
(see meiosis)
regulatory gene
A nontranscribed gene. Sometimes used to denote a structural gene engaged in the regulation of gene expression.
relative-rate test
A calibration-free test for checking the constancy of the rate of nucleotide substitutions in different lineages during their evolution, thus determining whether or not the molecular clock operates at the same rate among different lineages.
repetitive DNA
DNA sequences present in many copies in the haploid genome.
replacement
The result of a nonsynonymous substitution at the protein level.
replication
The process of DNA synthesis on a DNA template.
replication slippage
A process in which a certain sequence of DNA is used more than once in a row as a template during DNA replication, thus creating a tandemly repeated sequence in the newly synthesized DNA.
replicative transposition (duplicative transposition)
The insertion of a copy of a transposable element into a new chromosomal position while the element itself remains in the original position.
replicator gene
A regulatory gene specifying the sites for initiation and termination of DNA replication.
replicon
A chromosomal region that contains the DNA sequences necessary for the initiation of DNA replication, and that is replicated as a unit.
reproductive barrier (reproductive isolation)
Any of several biological or environmental mechanisms that prevent gene exchange between populations.
restriction endonuclease (restriction enzyme)
An enzyme that hydrolyzes internal phosphodiester bonds in the DNA.
restriction site
The point at which a restriction endonuclease hydrolyzes (cuts) an internal phosphodiester bond in the DNA. May or may not reside in proximity to the recognition sequence.
restriction-fragment pattern
The number and sizes of the restriction fragments resulting from a DNA sequence being digested by a restriction endonuclease.
restriction-site map
The schematic representation of a DNA sequence showing the location of the restriction sites.
retroelement
A DNA or RNA sequence that possesses the ability to produce reverse transcriptase.
retrofection
The process of transfer of an RNA molecule from one cell to another, in particular to a germ-line cell, by means of a retroviral particle, into which the RNA is encapsulated; the RNA is then reverse-transcribed and incorporated into the host genome. Transduction by means of a retrovirus.
retrogene (processed gene)
A functional retrosequence producing a protein that is identical or nearly identical to that produced by the gene from which the mRNA was derived.
retron
A genomic sequence encoding reverse transcriptase but lacking the ability to transpose.
retroposition
An RNA-mediated mode of transposition.
retroposon
A transposable retroelement that neither constructs virion particles nor is flanked by terminally redundant sequences.
retropseudogene (processed pseudogene)
A pseudogene derived from the reverse transcription of an RNA molecule and subsequent incorporation of the cDNA into the genome. Diagnostic signs include lack of introns, polyadenine tails, flanking repeats, truncation, evidence of posttranscriptional modifications, and lack of physical linkage with either functional or nonprocessed functionless members of the gene family.
retrosequence (retrotranscript, processed sequence)
A genomic sequence that has been derived through the reverse transcription of RNA but by itself lacks the ability to produce reverse transcriptase. Retrogenes and retropseudogenes.
retrotransposon
A transposable retroelement that does not construct virion particles and that is flanked by terminally redundant sequences.
retrovirus
Any of a group of small single-stranded RNA viruses that encode reverse transcriptase.
reverse transcriptase
The enzyme that catalyzes reverse transcription.
reverse transcription
The synthesis of a single-stranded DNA molecule on an RNA template.
ribonucleic acid (RNA)
A macromolecular polymer of linked nucleotides in which the sugar residue is ribose. Usually, single-stranded.
ribosomal RNA (rRNA)
The RNA molecules that constitute the structural components of a ribosome.
ribosome
An intracellular particle composed of rRNA and proteins that furnishes the site at which mRNA is translated.
RNA
(see ribonucleic acid)
rolling-circle replication
A mode of amplification in which a circular extrachromosomal copy of a DNA sequence is created and replicated in a continuous fashion.
root
In rooted trees, the common ancestor of all the taxa under study.
rooted tree
A phylogenetic tree that specifies ancestral and descendant species, thus indicating the direction of the evolutionary path.
rRNA
(see ribosomal RNA)