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Many mammoth questionsThe road to bringing back the mammoth — a giant that went extinct at the end of the last ice age — is filled with barriers.
The questions are almost never ending: Will scientists find ancient, uncontaminated mammoth DNA? How will they create new mammoths? If a mammoth calf is born, how will it learn how to behave without a parent or herd to guide it?
Beth Shapiro, a professor of ecology and evolutionary biology at the University of California, Santa Cruz, discusses these queries in "How to Clone A Mammoth: The Science of De-Extinction" (Princeton University Press, 2015). Here are 11 of the many challenges she considers, including those that are scientific, ethical and environmental.
DNA degradationSlide 2 of 23
DNA begins to degrade the moment an organism dies. This happens because enzymes from the body cells and environment and ultraviolet radiation from the sun start to break down the genetic code. Oxygen and water can also alter DNA, breakings its strands.
Some mammoth DNA, however, has survived because it was frozen in permafrost. Some of these frozen remains contain short fragments of DNA — mostly between 30 to 90 base pairs long (one base pair is made up of two "letters" of DNA linked together: cytosine and guanine, or adenine with thymine). To put this number in perspective, there are 3 billion base pairs in the human genome.
Researchers have collected these short, mammoth DNA fragments for years, but they still don't have enough to compile an entire mammoth genome, according to "How To Clone a Mammoth."Slide 3 of 23
DNA contaminationSlide 4 of 23
DNA contaminationEven if pieces of preserved ancient DNA are uncovered, they might be contaminated with foreign DNA from fungus, bacteria, plants, animals and even from humans handling it for research purposes.
This DNA contamination can make it difficult for researchers to know which DNA molecule belongs to the animal, and which is from contamination, especially if the extinct animal doesn't have a living relative whose DNA can serve as a roadmap, Shapiro wrote.Slide 5 of 23
Close relativesSlide 6 of 23
Scientists have only fragments of mammoth DNA, but they can use DNA from the mammoth's close relatives — modern-day elephants — to help fill in the genetic gaps.
Mammoths are more closely related to Asian elephants (Elephas maximus) than they are to African elephants. Researchers in India published the Asian elephant genome in a 2015 study in the Journal of Biosciences, and another effort is underway at the Broad Institute in Cambridge, Massachusetts.
The mammoth and the Asian elephant diverged about 2.5 million to 5 million years ago. If they, let's say, diverged about 4 million years ago, then about 2 percent of their genomes would be different, amounting to 70 million genetic differences, Shapiro wrote.
It will be difficult to learn what those differences are, meaning that if scientists were to recreate the mammoth, it wouldn't be an exact mammoth, but rather a hybrid.Slide 7 of 23
Back breedingSlide 8 of 23