Reproductive Character Displacement
The increased reproductive isolation between two closely related species when they live in the same geographic region (sympatry) as compared with when they live in separated geographic regions. A kind of character displacement in which the character concerned influences reproductive isolation, not ecological competition.

Restriction Enzyme Cutting Site.
A specific nucleotide sequence of DNA at which   particular restriction enzyme cuts the DNA. Some sites occur frequently in DNA (e.g., every several hundred base pairs); others much less frequently (rate-cutter; e.g., every 10,000 base pairs).

Replication
The process of DNA synthesis

Replication Fork
The Y-shaped region of a piece of DNA associated with the site of replication

Replicon
The amount of DNA that is replicated beginning at a single origin of replication.

Reporter Gene
See: marker    

Restriction Fragment
A fragment of DNA produced by cleavage of a larger DNA molecule with one or more restriction enzymes.

Restriction Fragment Length Polymorphism (RFLP)
Variation between individuals in DNA fragment sizes cut by specific restriction enzymes; polymorphic sequences that result in RFLPs are used as markers on both physic maps and genetic linkage maps. RFLPs usually are caused 'y mutation at a cutting site.
2. A genetic difference between individuals in a population detected by observing differences in restriction fragment lengths.

Restriction Endonuclease
A nuclease, derived frommicroorganisms, that recognizes a specific DNA sequence (usually a sequence of four to ten nucleotides) and nicks or cleaves the DNA at or near that site.