D-loop

A diagram in the paper introducing the term illustrated the D-loop with a shape resembling a capital "D", where the displaced strand formed the loop of the "D".

Researchers at Caltech discovered in 1971 that the circular mitochondrial DNA from growing cells included a short segment of three strands which they called a displacement loop.

[citation needed] Replication of the mitochondrial DNA can occur in two different ways, both starting in the D-loop region.

The more recently reported mode starts at a different origin within the D-loop region and uses coupled-strand replication with simultaneous synthesis of both strands.

[7] The function of the D-loop is not yet clear, but recent research suggests that it participates in the organization of the mitochondrial nucleoid.

[10] In 1999 it was reported that telomeres, which cap the end of chromosomes, terminate in a lariat-like structure termed a T-loop (Telomere-loop).

This makes use of the intact chromosome homologous to the broken one as a template to bring the two double-stranded pieces into correct alignment for rejoining.

A current model of meiotic recombination, initiated by a double-strand break or gap, followed by pairing with an homologous chromosome and strand invasion to initiate the recombinational repair process. Repair of the gap can lead to crossover (CO) or non-crossover (NCO) of the flanking regions. CO recombination is thought to occur by the Double Holliday Junction (DHJ) model, illustrated on the right, above. NCO recombinants are thought to occur primarily by the Synthesis Dependent Strand Annealing (SDSA) model, illustrated on the left, above. Most recombination events appear to be the SDSA type.