[daily Study] 5 Most Cloned Animals

[영어도우미]

5 Most Cloned Animals

by Jennifer Horton

Animal 1: Cloned Mice

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Three generations of cloned mice.

These ever-popular laboratory animals, mice are in even greater demand with the advent of reproductive cloning. The first cloned mouse, Cumulina, was born in July 1998 -- more than 10 years ago. And she wasn't alone: While it took Dolly's creators 277 tries before they had any success, Cumulina was the firstborn of ten identical siblings. Within five months, her creators had manufactured more than 60 clones [source: Caldwell].

Since mice are usually the most desirable animals for biomedical research, the possibility of having an endless supply of genetically identical rodents has caused quite a stir. Since Cumulina, the cloning process for mice has become even more successful. A study in 2007 discovered a cloning technique that achieved almost five times the success rate as the typical method [source: HHMI].

­M­ice, along with rats and birds, make up around 95 percent of the animals currently used in research [source: AAVS]. That will likely translate into thousands upon thousands of little cloned mice. Although there aren't any official numbers since facilities aren't required to report the number of animals they clone (or even use), it goes without saying that scientists will make use of cloning technologies in their studies. While that may not be good news for the mice, or for those individuals who oppose animal research, at least it earned the little guys a top spot on the list of most cloned animals.

 

Animal 2: Cloned Cattle

They've recently received a lot of flack for the excessive amount of methane gas they contribute to the atmosphere, but cows aren't going anywhere any time soon -- especially now that farmers can clone their best specimens to produce top-notch herds.

Cloning is simply an easier way for farmers to do what they've always done -- improve their stock by selectively breeding those animals with the most desired characteristics. Want consistently tender steak? Clone Butch. Want delicious, rich milk? Make some copies of old Bessie.

Cloning Controversy

Some people oppose cloning on both safety and ethical grounds. For every successful clone, they argue, thousands of embryos are lost, not to mention the fact that cloned animals are often riddled with health complications that shorten their lives. According to some estimates, more than 90 percent of cloning attempts fail, and even when they do succeed, the animal may die soon afterward. The endangered guar that was cloned in 2001 survived a mere 48 hours [source: Keim, Science News, Human Genome Project].

­If the thought of consuming products from cloned cattle turns your stomach, take heart: It's probably their traditionally conceived offspring that will make it into the food supply. Since cloning a cow costs between $10,000 and $20,000 (compared to a mere $50 for one created the old-fashioned way), the cloned animals will likely be used for breeding purposes only [source: Sharples].

Currently, two U.S. companies, Trans Ova Genetics and ViaGen, offer cloning services to cattle breeders. ViaGen churns out around 150 cloned cows annually, while Transova expected 250 in 2007 alone [source: Sharples, Trans Ova]. The European Food Safety Authority approximates that there are around 4,000 cloned cattle worldwide [source: EFSA].

 

Animal 3: Cloned Pigs

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All together now: awwww

If all pigs were as good at spelling as Wilbur, you might be a li­ttle more stoked about this particular selection. But while pigs can't spell -- it was Charlotte's doing, after all -- they do make some pretty mean bacon. If meat isn't your thing, cloned pigs are also sought after because of the suitability of their organs for human transplantation.

Transferring cells, tissues or organs from one species to another is known as xenotransplantation and is viewed as a potential solution to the shortage of organs and cells for lifesaving transplants. By tweaking the genetic makeup of pigs, a biopharmaceutical company named PPL Therapeutics has fine-tuned the animals' DNA so some of their organs and cells can be used successfully in people. These genetically altered pigs can be cloned to mass-generate things like insulin-producing cells for the treatment of type 1 diabetes and organs like hearts and kidneys [source: PPL Therapeutics, Inc.].

According to the European Food Safety Authority (EFSA), which recently conducted a study on the safety of products obtained from cloned animals and their offspring for consumption, there are already at least 500 cloned pigs in existence worldwide [source: EFSA]. And like goats, porcine foodstuffs also got the green light from the FDA, so it's likely that the number of pigs being cloned will increase. As advancements continue to be made with the treatment of human disease and xenotransplantation, pigs should continue to stake out a pretty prominent spot on the list of most cloned animals.

Animal 4: Cloned Goats and Sheep (It's a Tie)

For most people, it's probably more exciting to imagine clones of Fido running around the house than livestock clones bumbling around the farm. But to scientists and breeders, cloned goats and sheep are simply captivating and hold a lot of promise.

Sheep, for instance, can be genetically engineered to produce drugs that are useful in treating human diseases. One example is Polly, a cloned lamb designed to produce milk containing a protein that's deficient in hemophiliacs. Theoretically, sheep like Polly could be mass-produced to churn out medicinal drugs [source: Pecorino].

Ode to Dolly

Dolly captured our hearts and minds with her monumental birth in 1996. It could be said that this endearing sheep kicked off the mass interest in cloning. Dolly lived out her years at the Roslin Institute in Scotland and was the mother of six lambs born the old-fashioned way. Sadly, Dolly was euthanized on Valentine's Day 2003 due to crippling arthritis and lung cancer. She was only 6 years old.

­Fuzzy sheep are yet another benefit of cloning. Breeders have manually tinkered with their herds for years to get extra-woolly critters, and cloning enables them to easily perpetuate the genetics of those individuals that provide them with the most wool, thus creating a more bountiful product.

Likewise, some goats are cloned to produce herds that yield higher quality milk and meat products. Goat cloning got an additional boost by being one of the three species OK'd by the FDA in January 2008 for human consumption. There's no question breeders will take advantage of that decision to maximize the desirable traits of their Billys.

 

Animal 5: Cloned Pets

In 2005, scientists in South Korea announced they had produced the first dog clone -- an Afghan hound named Snuppy. Several years earlier, in late 2001, the world's first cloned kitten, CC (short for Copycat), entered the world. Since then, at least 40 dogs and an unknown number of cats have been replicated [source: Keim].

In July 2008, BioArts International auctioned off four dog cloning spots to the highest bidders. The program, aptly titled "Best Friends Again," also offered up one, all-expenses-paid spot for a lucky winner in its Golden Clone Giveaway contest. That spot has since been won by a heroic Sept. 11 rescue dog, dubbed the world's most "clone-worthy" dog [source: BioArts International].

Handout/Getty Images
Snuppy and his donor daddy.

Hund­reds of people ­pay upward of $1,000 a year to preserve tissue from their cat or dog for future cloning [source: Shiels]. Despite the high demand for commercially cloned pets, BioArts states on its Web site that its Best Friends Again program is a limited service that may or may not be continued.

Surely someone will step up to the plate, which is why pets merit a spot on this list. With thousands of potential customers having expressed interest in duplicating their beloved pets, it's only a matter of time before the technology advances enough to support a commercial venture.

Indeed, the Seoul-based company RNL Bio recently opened its doors for business and after the birth of five cloned puppies in August 2008, announced itself as the "first successful commercial canine cloning service." The team has already cloned more than 20 dogs and has plans to clone about 300 per year [source: CNN]. So if you have $150,000 to spare and a beloved pug to duplicate, you may want to take a trip to South Korea.

 

Source: www.howstuffworks.com

Vocabulary:

cloning - to produce a copy or imitation of
advent - a coming into place, view, or being
biomedical - the application of the natural sciences, esp. the biological and physiological sciences, to clinical medicine
crippling - to disable; impair
therapeutics - of or pertaining to the treating or curing of disease

Discussion Questions:

1. What was your reaction after reading the article?

2. What is cloning?

3. How can cloning be useful to humans? Why? 

4. Do you think that it is immoral to clone animals? Why? Why not? 

5.  What are the advantages and disadvantages of cloning?