By Phillip Jones
While the words “cloning” and “danger” conjure up visions of the ferocious dinosaurs in Michael Crichton’s Jurassic Park (1990), the true threat of cloning does not reside in the cloned animals. To be more precise, the process of cloning is perilous to the health of the animals involved.
Scientists are attempting to return certain extinct species to the planet in an endeavor called “de-extinction.” An example of this undertaking is the bucardo, a wild goat that lived for thousands of years in the mountain range between France and Spain. Humans hunted the bucardo to the threshold of extinction until 1999, when a single bucardo remained. Then, a rotten tree fell on the goat—a female named Celia—and terminated the entire species. Before Celia died, a scientist removed a small piece of skin and then froze the tissue.
To resurrect the bucardo species, scientists decided to clone Celia using a technique called “nuclear transfer.” The scientists obtained goat egg cells and removed the nuclei (the heart of cells that contains the DNA). After isolating nuclei from Celia’s preserved skin cells, they injected them into the goat eggs. The scientists implanted the eggs in female goats and then waited to see if the surrogate mothers would succeed in birthing Celia clones.
The motivation driving cloning efforts is the creation of breeding stock with certain traits. These traits include increased resistance to disease and enhanced suitability for the changing climate.
Figure 1: Sheep Cloning Process
Image Source: European Society of Dog and Animal Welfare
In 1997, Ian Wilmut of Scotland’s Roslin Institute proclaimed the birth of the first livestock animal cloned from an adult. Wilmut and his colleagues isolated cells from mammary gland tissue of an adult Finn-Dorset sheep as nuclei donor cells. The scientists then obtained egg cells from a Scottish blackface sheep, removed the nuclei from the egg cells, and fused pairs of egg cells and donor cells by treating them with electricity. The shock treatment also activated the fused cells to begin development into embryos. The researchers then transferred the embryos into the uteruses of Scottish blackface sheep—the surrogate mothers. The cloned sheep (named Dolly) had characteristics of a Finn-Dorset lamb—the type of sheep that donated the nucleus.
So, how is cloning hazardous to animal health?
The scientists who attempted to clone Celia the goat produced seven pregnant goats from 57 implantations. Six of the goats miscarried. The only Celia clone—delivered by cesarean section—struggled to breathe and then died 10 minutes later. A necropsy revealed that one of the clone’s lungs had a massive additional lobe of solid tissue.
Dolly the sheep—the harbinger of a new cloning age—suffered from early-onset arthritis. The animal died at about half the anticipated life expectancy from a type of lung disease most common in older sheep. Because Dolly was cloned with cells from a six-year-old sheep, this suggested that she aged prematurely. Beginning life with an older nucleus probably doomed the clone.
Cloning animals has uncovered a minefield of unanticipated problems. Nuclear transfer cloning has a success rate that ranges from 0.1 percent to three percent according to the Genetic Science Learning Center at the University of Utah. Clones that somehow manage to survive to birth tend to have abnormally large organs that cause problems—such as breathing difficulties and poor blood flow. Clones may also develop kidney or brain deformities and weakened immune systems, leaving the clones susceptible to diseases.
1. Which ONE sentence below from Passage 1 BEST supports the author’s central argument?
A“The shock treatment also activated the fused cells to begin development into embryos.”
B"The only Celia clone—delivered by cesarean section—struggled to breathe and then died 10 minutes later.”
C“Beginning life with an older nucleus probably doomed the clone.”
D“The motivation driving cloning efforts is the creation of breeding stock with certain traits.”
1 answer
B "The only Celia clone—delivered by cesarean section—struggled to breathe and then died 10 minutes later."
This sentence best supports the author’s central argument about the health hazards associated with cloning animals, highlighting a specific and dire outcome of the cloning process.
