Perhaps the " high-water mark " of phenetics were the DNA-DNA hybridization studies by Charles G. Sibley, Jon E. Ahlquist and Burt L. Monroe Jr., from which resulted the 1990 Sibley-Ahlquist taxonomy for birds.

These base pairs have a higher thermal stability ( melting point, see also DNA-DNA hybridization ) than adenine-thymine, a property that might convey, among organisms living in high-temperature environments, a selective advantage on variants enriched in GC content.

The use of techniques such as DNA-DNA hybridization to study evolutionary relationships was pioneered by Charles Sibley and Jon Edward Ahlquist resulting in what is called the Sibley-Ahlquist taxonomy.

However, the resolution of the DNA-DNA hybridization technique used by Sibley & Ahlquist was not sufficient to properly resolve the relationships in this group, and indeed it appears as if the Charadriiformes consititute a single large and very distinctive lineage of modern birds of their own.

Following the development of research techniques in molecular biology in the late 20th century, in particular methods for studying DNA-DNA hybridization, a great deal of new information has surfaced, much of it suggesting that many birds, although looking very different from one another, are in fact more closely related than was previously thought.

Molecular studies such as DNA-DNA hybridization ( Sibley & Ahlquist, 1990 ) and sequence analyses fail to resolve the relationships of grebes properly due to insufficient resolution in the former and long-branch attraction in the latter.

* ( 1988 ): A classification of the living birds of the world based on DNA-DNA hybridization studies.

In the period of 1974 – 1986, DNA-DNA hybridization was the dominant technique.

In the period of 1974 – 1986, DNA-DNA hybridization was the dominant technique.

This was confirmed by Sibley & Ahlquist ( 1990 ) based on DNA-DNA hybridization and subsequently by Paton et al.

Sibley and Ahlquist furthermore removed button-quails ( Turnicidae ) from the Gruifomes based on large DNA-DNA hybridization distances to other supposed Gruiformes.

It is based on DNA-DNA hybridization studies conducted in the late 1970s and throughout the 1980s.

DNA-DNA hybridization is among a class of comparative techniques in molecular biology that produce distance data ( versus character data ) and that can be analyzed to produce phylogenetic reconstructions only using phenetic tree-building algorithms.

In DNA-DNA hybridization, the percent similarity of DNA between two species is estimated by the reduction in hydrogen bonding between nucleotides of imperfectly complemented heteroduplex DNA ( i. e., double stranded DNAs that are experimentally produced from single strands of two different species ), compared with perfectly matched homoduplex DNA ( both strands of DNA from the same species ).

However the classification study did not employ modern cladistic methods, as it relies strictly on DNA-DNA hybridization as the sole measure of similarity.

Initial mtDNA cytochrome b sequence analysis ( Mariaux & Braun 1996 ) agreed with earlier morphological ( Cracraft 1981 ) and DNA-DNA hybridization ( Sibley & Ahlquist 1990 ) studies insofar as that the oilbird and the frogmouths seemed rather distinct.

The swallows and martins are morphologically unique within the passerines, but the use of DNA-DNA hybridization studies has suggested relationships with the Old World warblers ( a large wastebin taxon that has recently been split into several new families ), the white-eyes and the tits.

This makes the expanded Sturnidae a rather noninformative group and is probably due to the methodological drawbacks of their DNA-DNA hybridization technique.

Estimate of relationships among subgenera based on DNA-DNA hybridization.

The Sibley-Ahlquist taxonomy elevated them to ordinal status as the Turniciformes and basal to other Neoaves either because their accelerated rate of molecular evolution exceeded the limits of sensitivity of DNA-DNA hybridization or because the authors did not perform the appropriate pairwise comparisons or both.

Morphological, DNA-DNA hybridization and sequence data indicate that turnicids correctly belong to the shorebirds ( Charadriiformes ).

However, the grouping of Sibley & Monroe ( besides leaving the subfamily rank vacant ) is overly coarse due to methodological drawbacks of their DNA-DNA hybridization technique and most of their proposed revisions of taxonomic rank have not been accepted ( see for example Ciconiiformes ).

* Sheldon, Frederick H .; McCracken, Kevin G. & Stuebing, Keeley D. ( 1995 ): Phylogenetic relationships of the zigzag heron ( Zebrilus undulatus ) and white-crested bittern ( Tigriornis leucolophus ) estimated by DNA-DNA hybridization.

DNA-DNA hybridization generally refers to a molecular biology technique that measures the degree of genetic similarity between pools of DNA sequences.

The Bearded Reedling tended to appear close to larks in phylogenies based on e. g. DNA-DNA hybridization ( Sibley & Ahlquist 1990 ), or on mtDNA cytochrome b and nDNA c-myc exon 3, RAG-1 and myoglobin intron 2 sequence data ( Ericson & Johansson 2003 ).

Sim4 is a nucleotide sequence alignment program akin to BLAST but specifically tailored to DNA to cDNA / EST ( Expressed Sequence Tag ) alignment ( as opposed to DNA-DNA or protein-protein alignment ).

This placement of both the Black-necked Stork and Saddle-billed Stork under the same genera was later supported by osteological and behavioural data, and DNA-DNA hybridisation and Cytochrome-b data.

Notably, distance methods allow use of data that may not be easily converted to character data, such as DNA-DNA hybridization assays.

Following the development of research techniques in molecular biology in the late 20th century, in particular methods for studying DNA-DNA hybridisation, a great deal of new information has surfaced, much of it suggesting that many birds, although looking very different from one another, are in fact more closely related than was previously thought.

In their pioneering DNA-DNA hybridisation work, Sibley and Ahlquist found that the genetic difference between the eared-nightjars and the typical nightjars was, in fact, greater than that between the typical nightjars and the nighthawks of the New World.

Sibley & Ahlquist ( 1990 ) united the " Old World warblers " with the babblers and other taxa in a superfamily Sylvioidea as a result of DNA-DNA hybridisation studies.

Sibley and Ahlquist's landmark DNA-DNA hybridisation studies ( see Sibley-Ahlquist taxonomy ) led to them placing the families traditionally contained within the Pelecaniformes together with the grebes, cormorants, ibises and spoonbills, New World vultures, storks, penguins, albatrosses, petrels, and loons together as a sub-group within a greatly expanded order Ciconiiformes, a radical move which by now has been all but rejected: their " Ciconiiformes " merely assembled all early advanced land-and seabirds for which their research technique delivered insufficient phylogenetic resolution.

By the early 1970s Sibley was pioneering DNA-DNA hybridisation studies, with the aim of discovering, once and for all, the true relationships between the modern orders of birds.

The relationship of the Petroicidae to other bird families is uncertain ; Sibley and Alquist's DNA-DNA hybridisation studies had placed them in the Corvoidea ( a huge group that includes the shrikes, crows and jays, butcherbirds, woodswallows, drongos, cuckoo-shrike, fantails, monarch flycatchers and many others ).

Charles Sibley and Jon Ahlquist, pioneers of the technique, used DNA-DNA hybridization to examine the phylogenetic relationships of avians ( the Sibley-Ahlquist taxonomy ) and primates.

On the other hand, DNA-DNA hybridization ( Sibley & Ahlquist 1990 ) placed the white-eyes closer to Sylvia.

The Sibley-Ahlquist taxonomy of birds, based upon DNA-DNA hybridization, suggested that the Limpkin's closest relatives were the Heliornithidae finfoots, and Sibley and Monroe even placed the species in that family in 1990.

Sibley and Ahlquist in 1990 considered it likely to be a basal cuckoo based on DNA-DNA hybridization.

Thamnophilidae was removed from Formicariidae, leaving behind the antthrushes and antpittas, due to recognition of differences in the structure of the breastbone ( sternum ) and syrinx, and Sibley and Ahlquist's examination of DNA-DNA hybridisation.

According to Sibley and Ahlquist's DNA-DNA hybridization studies the Tyranni can be divided into three suborders: Acanthisittides, Eurylaimides, and Tyrannides.

On the basis of the DNA-DNA hybridization studies of Sibley and Alhquist its closest relatives have now been identified as the leafbirds.

Their relationship with the Australian radiation of passerines was suggested by S. A. Parker on the basis of egg colour, nest structure and nestling plumage, and their position in this radiation was vindicated by Sibley and Ahlquist's DNA-DNA hybridization studies.

* 1981 – Sibley and Ahlquist use DNA-DNA hybridisation to determine degrees of genetic similarity between species.

Sibley and Ahlquist's DNA-DNA hybridisation studies placed the robins in a Corvida parvorder comprising many tropical and Australian passerines including pardalotes, fairy-wrens and honeyeaters as well as crows.