Essential Cell Biology 5th edition

Model Organisms
29
Figure 1–34 Drosophila melanogaster is a
favorite among developmental biologists
and geneticists. Molecular genetic studies
on this small fly have provided a key to the
understanding of how all animals develop.
(Edward B. Lewis. Courtesy of the Archives,
California Institute of Technology.)
1 mm
Model Animals Include Flies, Worms, Fish, and Mice
Multicellular animals account for the majority of all named species of
living organisms, and the majority of animal species are insects. It is fitting,
therefore, that an insect, the small fruit fly Drosophila melanogaster
(Figure 1–34), should occupy a central place in biological research. The
foundations of classical genetics (which we discuss in Chapter 19) were
ECB5 e1.33/1.34
built to a large extent on studies of this insect. More than 80 years ago,
genetic analysis of the fruit fly provided definitive proof that genes—the
units of heredity—are carried on chromosomes. In more recent times,
Drosophila, more than any other organism, has shown us how the genetic
instructions encoded in DNA molecules direct the development of a fertilized
egg cell (or zygote) into an adult multicellular organism containing
vast numbers of different cell types organized in a precise and predictable
way. Drosophila mutants with body parts strangely misplaced or
oddly patterned have provided the key to identifying and characterizing
the genes that are needed to make a properly structured adult body, with
gut, wings, legs, eyes, and all the other bits and pieces—all in their correct
places. These genes—which are copied and passed on to every cell
in the body—define how each cell will behave in its social interactions
with its sisters and cousins, thus controlling the structures that the cells
can create, a regulatory feat we return to in Chapter 8. More importantly,
the genes responsible for the development of Drosophila have turned out
to be amazingly similar to those of humans—far more similar than one
would suspect from the outward appearances of the two species. Thus
the fly serves as a valuable model for studying human development as
well as the genetic basis of many human diseases.
Another widely studied animal is the nematode worm Caenorhabditis
elegans (Figure 1–35), a harmless relative of the eelworms that attack the
QUESTION 1–7
Your next-door neighbor has
donated $100 in support of cancer
research and is horrified to learn
that her money is being spent on
studying brewer’s yeast. How could
you put her mind at ease?
0.2 mm
Figure 1–35 Caenorhabditis elegans is
a small nematode worm that normally
lives in the soil. Most individuals are
hermaphrodites, producing both sperm and
eggs (the latter of which can be seen just
beneath the skin along the underside of the
animal). C. elegans was the first multicellular
organism to have its complete genome
sequenced. (Courtesy of Maria Gallegos.)