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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.
Scientists have pieced together the genomes of four different mammoths over the past few years, but more hurdles remain: If researchers decide to create new mammoths, how will they do it? 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.
Editor's note: This story was updated on Sept. 15, 2017, to include the fact that several mammoth genomes are now available.
DNA degradationSlide 2 of 23
DNA begins to degrade the moment an organism dies. This happens because enzymes from the body cells and environment, as well as 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.
However, researchers are working around this "short fragment" challenge by using the modern elephant genome as a scaffold, Shapiro told Live Science.Slide 3 of 23
DNA contaminationSlide 4 of 23
Anient DNA is often 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.
Luckily, this isn't a big deal for mammoths, because "we can distinguish mammoth [DNA] from human and bacteria [DNA]," she told Live Science.Slide 5 of 23
Close relativesSlide 6 of 23
Scientists may 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 described the Asian elephant genome in 2015 in the Journal of Biosciences, and another effort is underway at the Broad Institute in Cambridge, Massachusetts, to sequence the genome of an Asian elephant.
The mammoth and the Asian elephant diverged between about 2.5 million and 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.
"The reads that I get are short, but — as long as there is a close relative that has a sequenced genome — I can still map those short reads onto that closest relative's genome and, piece by piece, put the genome together," Shapiro told Live Science in an email, referring to the "reads" of a DNA sequence. "There will be missing pieces … but it will be mostly there."Slide 7 of 23
Back breedingSlide 8 of 23