Scientists from Spain, USA and Canada construct a physical map of the Drosophila buzzatii genome

A useful tool for evolution studies

An international team of researchers led by the Universitat Autònoma de Barcelona Professor Alfredo Ruiz, has launched in this month’s issue of the journal Genome Research the first detailed physical map of the Drosophila buzzatii chromosomes. This fly species is used worldwide as a model for studies in evolutionary genetics.

The investigation involved two steps. First, a genomic library was produced. This library comprises more than 18.000 random fragments of the fly’s genome inserted within bacterial cells. Each bacterial clone carries one of these DNA fragments, about 150.000 nucleotides long, and can be multiplied in a laboratory culture to amplify the fly’s DNA.

The second step involved arranging the random fragments present in the library in the same order and position as they are in the intact chromosomes. This amounts to composing a puzzle with thousands of pieces. Two methods were used for this task. One of them is called “fingerprinting” and consists in cutting the original clones into smaller fragments and then sizing these fragments by electrophoresis. The computerized comparison of the fragments produced by different clones (their “fingerprints”) allows to determine which clones overlap and belong to the same chromosomal region. The second method required the hybridization of the genomic clones to the giant salivary gland chromosomes of the larvae, a technique known as “in situ hybridization” which allows locating the chromosomal position of each clone (see image).

The physical map of Drosophila buzzatii genome is one of the most detailed maps ever built in Drosophila. Its interest stems from the species Drosophila buzzatii, which is widely used in studies of genome evolution, ecological adaptation and speciation. Now, thanks to the genomic library and the physical map, the international research community will find it easier to compare the genomes of this and related species, and to assemble the reads when the genomes of these species are sequenced.

The research has been coordinated by Professor Alfredo Ruiz from the Departament of Genetics and Microbiology of the UAB (Spain), and the team included 13 other investigators from this university and from the Children’s Hospital Oakland Research Institute in Oakland, California (USA); the Genome Sciences Centre in Vancouver (Canada); and the Lawrence Berkeley National Laboratory, in Berkeley, California (USA).