II. Reading Activities.

2. Read the text below using a dictionary. Two Worms Are Better Than One

Mark Patterson, Innovations Report

Caenorhabditis elegans, a 1-mm soil-dwelling roundworm with 959 cells, may be the best-understood multicellular organism on the planet. As the most "pared-down" animal that shares essential features of human biology from embryogenesis to aging C. elegans is a favorite subject for studying how genes control these processes. The way these genes work in worms helps scientists understand how diseases like cancer and Alzheimer's develop in humans when genes malfunction. With the publication of a genome sequence of C. elegans' first cousin, C. briggsae, Lincoln Stein and colleagues have greatly enhanced biologists' ability to mine C. elegans for biological gold.

Confirming the accuracy of the sequence (it covers 98% of the genome and has an accuracy of 99.98%), the researchers turned to the substance of the genome. Examining the two worm genomes side by side, scientists can quickly spot genes and flag interesting regions for further investigation. Analyzing the organization of the two genomes, Stein et al. not only found strong evidence for roughly 1,300 new C. elegans genes, but also indications that certain regions could be "footprints of unknown functional elements." While both worms have roughly the same number of genes (about 19,000), the C. briggsae genome has more repeated sequences, making its genome slightly larger. The size is estimated to be just over 100 million base pairs, about 1/30 the size of the human genome.

Because the worms set out on separate evolutionary paths about the same time mice and humans parted ways - about 100 million years ago, compared to 75 million years ago - the authors could compare how the two worm genomes have diverged with the divergence between mice and humans. The worms' genomes, it seems, are evolving faster than their mammalian counterparts, based on the change in the size of the protein families (C. elegans has more chemosensory proteins than C. briggsae, for example), the rate of chromosomal rearrangements, and the rate at which silent mutations (DNA changes with no functional effect) accumulate in the genome. This would be expected, the researchers point out, because generations per year are a better measure of evolutionary rate than years themselves. (Generations in worms are about three days; in mice, about three months.)

What is surprising, they say, is that despite these genomic differences, the worms look nearly identical and occupy similar ecological niches; this is obviously not the case with humans and mice, which nevertheless have remarkably similar genomes. It's the quality, rather than the quantity of the changes in the genome, that's important. The nature of these changes, along with many other issues, can now be explored by searching the two species' genomes and comparing those elements that have been conserved with those that have changed.

With the C. briggsae genome sequence in hand, worm biologists have a powerful new research tool. By comparing the genetic makeup of the two species, C. elegans researchers can refine their knowledge of this tiny human stand-in, fill in gaps about gene identity and function, as well as illuminate those functional elements that are harder to find, and study the nature and path of genome evolution.

B. Look through the text again and translate the following parts from English into Russian:

― soil-dwelling roundworm

― Lincoln Stein and colleagues have greatly enhanced biologists' ability to mine C. elegans for biological gold

― Confirming the accuracy of the sequence, the researchers turned to the substance of the genome.

― Examining the two worm genomes side by side, scientists can quickly spot genes and flag interesting regions

― found strong evidence for roughly 1,300 new C. elegans genes

― the size is estimated to be just over 100 million base pairs

― occupy similar ecological niches

― fill in gaps about gene identity

― researchers can refine their knowledge of this tiny human stand-in

― illuminate those functional elements that are harder to find

C. Read the text again and answer the following questions in your own words.

1. Why are Caenorhabditis elegans considered to be the best-understood multicellular organism on the planet?

2. How does the worms’ genome evolve?

3. What kinds of worms are mentioned in the reading? Basing on the text, give as much information about them as possible.

4. How are worms connected with humans in the reading?

5. What are the reasons of the fact that the worms' genomes are evolving faster than mammalian ones?

6. What is the use of C.elegans in science?

7. What is the evidence of fast progress of the worms' genomes? 8. Why do the scientists study the genomes of C. briggsae and C. elegans simultaneously?

9. Why is it important to find out the way the worms' genomes work?

10. Why do two kinds of worms differ from each other more than human and mice do?

11. What is silent mutation according to the reading? 12. What is the mechanism of spotting genes?

D. The text below has been jumbled. Arrange the paragraphs in the correct order to make a full story.

Rain worms.

(1) A further theory is that, as there are many other organisms in the ground as well, and their respiration increases carbon dioxide, this gas may dissolve into the rainwater to form carbonic acid. As the soil becomes too acidic for the worms, they seek a more neutral environment on the surface.

(2) An alternative theory concerning this behaviour is that as some species (notably Lumbricus terrestris) come to the surface to mate they may become stranded. However, as this behaviour is limited to only a few species and L. terrestris is rarely, if ever, one of those found stranded on impermeable surfaces, this theory does not seem a very likely explanation.

(3) Earthworms are seen on the surface after large rain storms flood the soil because, despite needing a moist environment to allow the diffusion of gases across their skin membrane, where the soil becomes saturated they begin to drown. To protect themselves they escape to the surface but if the ground is unnaturally hard they may become stranded and die from exposure. This is why they are seen in places like driveways after a storm. However, this theory is not applicable to certain earthworm species that can survive immersion for several days in oxygenated water.

(4) Another theory is that the worms may be using the moist conditions on the surface to travel more quickly than they can underground, thus colonizing new areas more quickly. Since the relative humidity is higher during and after rain, they do not become dehydrated. This is a dangerous activity in the daytime, since earthworms die quickly when exposed to direct sunlight with its strong UV content, and are more vulnerable to predators such as birds.