RAPD
Randomly amplified polymorphic DNA. A method of analysis where PCR amplification using two copies of an arbitrary oligonucleotide primer is used to create a multilocus fingerprint (i.e., band profile).

reciprocal monophyly
A genetic lineage is reciprocally monophyletic when all members of the lineage share a more recent common ancestor with each other than with any other lineage on a phylogenetic tree.

recombination
The process that generates a haploid product of meiosis with a genotype differing from both the haploid genotypes that originally combined to form the diploid zygote.

reintroduction
The introduction of a species or population into a historical habitat from which it had previously been extirpated.

relative fitness
A measure of fitness that is the ratio of a given genotype’s absolute fitness to the genotype with the greatest absolute fitness. Relative fitness is used to model genetic change by natural selection.

rescue effect
When immigration into an isolated deme (either genetically or demographically) reduces the probability of the extinction of that deme.

restriction enzyme
An enzyme (see endonuclease), isolated from bacteria, that cleaves DNA at a specific four or six nucleotide sequence. Over 400 such enzymes exist that recognize and cut over 100 different DNA sequences; used in RFLP, AFLP, and RAPD analysis and to construct recombinant DNA (in genetic engineering).

restriction fragment length polymorphism (RFLP)
A method of genetic analysis that examines polymorphisms based on differences in the number of fragments produced by the digestion of DNA with specific endonucleases. The variation in the number of fragments is created by mutations within restriction sites for a given endonuclease.

reverse mutation rate
Back mutation rate. The rate at which a gene’s ability to produce a functional product is restored. This rate is much lower than the forward mutation rate because there are many more ways to remove the function of a gene than restore it. Also used to describe mutation at microsatellite loci where (under the stepwise mutation model, for example) a back mutation yields an allele of length that already exists (i.e., homoplasy) in the population.

RFLP
See restriction fragment length polymorphism.

ribonucleic acid (RNA)
A polynucleotide similar to DNA that contains ribose in place of deoxyribose and uracil in place of thymine. RNA is involved in the transfer of information from DNA, programming protein synthesis, and maintaining ribosome structure.

Robertsonian fission
An event where a metacentric chromosome breaks near the centromere to form two acrocentric chromosomes.

Robertsonian fusion
An event where two acrocentric chromosomes fuse to form one metacentric chromosome.

Robertsonian translocation
A special type of translocation where the break occurs near the centromere or telomere and involves the whole chromosomal arm so balanced gametes are usually produced.