Biology Reference
In-Depth Information
The data banks can be searched over the web, but some caution is required
because errors apparently are common in both the data banks and scientific
journals. Errors, particularly in noncoding regions, may arise from sequencing or
clerical errors. Submission of a sequence to a database in a machine-readable
form is a prerequisite for publishing in many journals (
Cinkosky et al. 1991
).
Methods of DNA sequence analysis using computer programs such as BLAST
and PAUP are described briefly in Chapter 12 on molecular systematics and are
described by
Mount (2004)
.
There are so many databases available on the web, each with useful informa-
tion on various aspects of molecular biology, that there are now databases of
databases (
Baxevanis 2001
).
7.10 A Brief History of the
Drosophila
Genome Project
The Human Genome Project was the reason the
Drosophila
Genome Project was
initiated. The Human Genome Project was one of the largest initiatives in the
history of biology and was one of the most controversial. To prepare for this
enormous undertaking, the genomes of the yeast
Saccharomyces cerevisiae
, the
nematode
Caenorhabditis elegans
, the fruit fly
D. melanogaster
, and the labora-
tory mouse
Mus musculus
were targeted for sequencing to develop and improve
methods before undertaking the larger human genome. Even these proposed
subprojects generated considerable controversy.
Controversy arose as to whether it was appropriate to spend resources to
sequence the
Drosophila
genome. Knowledge of the structure and function of
the
D. melanogaster
genome already was far greater than that for any other
multicellular organism (
Kafatos et al. 1991
), and some believed a
Drosophila
Genome Project
was unnecessary. The
D. melanogaster
genome is
≈
180 Mb of
DNA, a third of which is heterochromatin. The 120 Mb of euchromatin is on the
two large autosomes and the X; the fourth chromosome is mostly heterochro-
matin, with only
≈
1 Mb of euchromatin. By 1991,
≈
3800 different genes, approx-
imately a fourth of the total, already had been mapped by recombination
studies. Many had been associated cytogenetically with one of the 5000 bands
of the polytene-gland chromosomes. Approximately 3000 “transcription units”
had been placed on the cytogenetic map by localizing the DNA on specific poly-
tene chromosomes by
in situ
hybridization. Nearly 10% of the total genes, 1300
genes, in
D. melanogaster
already had been cloned and sequenced by individual
laboratories (
Rubin and Lewis 2000
). However, after the project was concluded it
was discovered that approximately one-third of the genes in
Drosophila
do not
have obvious phenotypes when mutated, making the sequencing project a use-
ful gene-discovery method.
