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READING ASSIGNMENT 1:
Caenorhabditis elegans (pronounced see-nor-hab-die-tuss ell-eh-ganz ) is a small, transparent roundworm that lives in soil and eats bacteria. A roundworm, which is also called a nematode, does not have a segmented body. This is one way to tell it apart from an earthworm.
A fully grown C. elegans adult worm is less than 1/16 of an inch long, and its body is made up of fewer than 1000 cells. That may seem like a lot of cells, but your body contains trillions of cells (one trillion equals 1000 X 1000 X 1000). Since C. elegans is clear, every cell in its body can be seen in the microscope. By carefully watching worms as they grew, scientists were able to learn how a fertilized C. elegans egg divides to form all the cells of an adult worm. This pattern of cell divisions is called the cell lineage.
Animals we are familiar with, such as dogs, cats, birds and flies, exist as one of two sexes: male and female. C. elegans is unusual. The two sexes of this nematode are males and hermaphrodites. C. elegans males, like other male animals, make only sperm. C. elegans hermaphrodites, unlike female animals, make both sperm and eggs. Since it makes both kinds of gametes, a hermaphrodite worm is self-fertile and does not have to mate with a male worm to reproduce. In fact, all by itself, a C. elegans hermaphrodite can produce 300 or more offspring!
C. elegans has a very short generation time, the length of time needed to develop from a fertilized egg into a mature adult. One day after the egg is fertilized by a sperm, it develops into a young animal, called a larva, which hatches and crawls away. Two days after hatching, the worm is a mature adult which can produce offspring. When it is a week old, a worm might already be a grandparent!
The first step in a genetic study is to find mutants, animals that develop abnormally. Since most mutants are very rare, many animals must be examined before an abnormal one is found. Because worms are small, self-fertile and have short generation time, it is easy to look at thousands of worms to find one that develops abnormally.
Another part of a genetic study is to learn how development goes wrong in a mutant. Since C. elegans develops from an egg into an adult in a few days and is transparent, a microscope can be used to see how a mutant worm develops. Since the worm's body contains fewer than 1000 cells, it is often possible to tell exactly which cells develop abnormally in a mutant.
A third part of genetics is to see how a mutation acts when it is passed from one generation to the next. Is it dominant or recessive? Since C. elegans is self-fertile and has a short generation time, it is possible to put a single mutant hermaphrodite on a plate and, in a few days, see how many of its offspring are normal and how many are mutant.
In summary, C. elegans is small, clear, self-fertile, contains fewer than 1000 cells and has a short generation time. These features make it very useful for genetic studies.
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