AP Biology class blog for discussing current research in Biology

Tag: de-extinction

Instead of Bringing Back Dinosaurs, These Scientists are Bringing Back the Extinct Christmas Island Rat

Majestic dinosaurs and mammoths on our planet both underwent extinction millions and millions of years ago. The Christmas Island rat? In 1908. De-extinction techniques, also known as resurrection biology, garnered popularity within the science world in the 1990s. The Encyclopedia Britannica defines it as, “the process of resurrecting species that have died out or gone extinct.” Here is how these scientists are attempting to bring back a rat species that you have probably never heard of, and what that can mean for the future.

De-extinction using CRISPR gene-editing


File:MaclearsRat-PLoSOne.png - Wikimedia Commons

path of extinction of the Christmas Island rat

The process of de-extinction with the Christmas Island rat is driven by the method of CRISPR gene-editing, which allows for the genome of organisms to be modified, or edited, meaning that an organism’s DNA can be changed by us humans. This allows for genetic material to be added, removed, or modified at specific locations said genome. The idea behind the de-extinction of an animal through CRISPR gene-editing is to take surviving DNA of an extinct species and compare it to the genome of a closely-related modern species, then use CRISPR to edit the modern species’ genome in the places where it differs from the extinct one. The edited cells can then be used to create an embryo implanted in a surrogate host.

CRISPR thought to be “genetic scissors”

Thomas Gilbert, one of the scientists on the team of this project, says old DNA is like a “book that has gone through a shredder”, while the genome of a modern species is like an intact “reference book” that can be used to piece together the fragments of its degraded counterpart.

What is the difference between a genome and a gene?

File:Human genome to genes.png

Gene depicted within genome

Genes, a word you are most likely familiar with, carry the information which determines our traits, or features/characteristics that are passed on to us from our parents. Like chromosomes, genes come in pairs. Each of your parents has two alleles of each of their genes, and each parent passes along just one to make up the genes you have. Genes that are passed on to you determine many of your traits, such as your hair color and skin color. Known dominant traits are dark hair and brown eyes, while known recessive traits are blonde hair and blue or green eyes. If the two alleles that you receive from your parents are the same, you are homozygous for that gene. If the alleles are different, you are heterozygous, but you only express the dominant gene.

Each cell in the human body contains about 25,000 to 35,000 genes, and genes exist in animals and plants as well. Each gene is a small section of DNA within our genomes. That is the link between them, and they are not the same.

Is this possible? Can we really bring back the dead?

Reconstructed image of the extinct woolly mammoth

See, CRISPR gene-editing itself is of great interest for having shown promising results in terms of human disease prevention and treatment for diseases and single-gene disorders such as cystic fibrosishemophilia, and sickle cell disease, and shows promise for more complicated illnesses such as cancer, HIV infection, and mental illness–not so much with de-extinction. Here’s a simple diagram displaying the process.


In this scenario, it is not looking very likely that these rats can come back. Gilbert and his team of 11 other scientists, through extensive processes and attention to small-detail, have in total reconstructed 95% of the Christmas Island rat genome. While 95% may be an A on a test, in regards to genomes, that 5% is crucial. In this case, the missing 5% is linked to the control of smell and immunity, meaning that if we were to bring this animal back, it would lose key functionality. Gilbert says 100% accuracy in genome reconstructing of this species is “never” going to happen.

The success of de-extinction is quite controversial in itself. Restoring extinct species can mean an increase in biodiversity and helping out our ecosystems which are suffering greatly from climate change.  However, research also suggests it can result in biodiversity loss through possibly creating invasive species (yes, I wrote this) or for other reasons.

While the science is interesting, the reality of the unlikeliness of de-extinction becoming a normal and official process is kind of dream-crushing. Who knows, maybe as technology advances, hopefully, we can make all of this happen without harmful side effects, aid our ailing ecosystems, and visit some mammoths on a safari vacation!

How CRISPR Technology Can Potentially Reverse Extinction

Though Christmas Island rats went extinct over one hundred years ago, Anna Gibbs in sciencenews describes how genetically modifying the Norway brown rat would essentially reincarnate the Christmas Island rat. CRISPR is a relatively new technology that can be used to edit the genes of animals and has changed the science world of extinction. It works by editing “an existing animal’s genome so that it resembles that of the desired extinct animal… making that proxy as similar to the extinct species”.

Gibbs explains how using this technology, scientists compared fragments of the extinct rat’s genetic makeup, the Christmas Island rat, to that of their living relative, the Norway brown rat. By taking DNA from two preserved skin samples of the Christmas IslanRattus norvegicus - Brown rat 04d rat, the scientists were able to recover 95% of their genome. They compared the samples of the extinct species with the Norway brown rat and found that their genomes were very similar, 95% to be exact. Because of evolutionary divergence between the two species, the last 5% of the genetic information was lost forever. The missing genes were mostly located in the regions that controlled the rat’s immune responses and sense of smell. If they were to edit the Norway brown rat’s genome to resemble that of the Christmas Island rat, the differences in smell would be detrimental to their survival. This tiny difference in their genomes would prevent scientists from being able to recover the extinction of the Christmas Island rat. 

Though the scientists didn’t intend on actually reincarnating the rats, Gilbert says that what they discovered “could prove useful for people working on even more ambitious projects, like bringing back the wooly mammoth”. The hurdles of CRISPR technology lie in the tiny details of genetic engineering, even the smallest difference can prevent de-extinction. Ben Novak, a leading scientist at a nonprofit that uses genetic engineering for conservation projects, says that though there are MaclearsRatSkullways to capture some of the missing data, “the fact that some data will always be missing is a limitation that de-extinction scientists have already come to terms with”. The goal of de-extinction isn’t to completely recreate the extinct species but rather to formulate a new species out of the old that will fool its environment and live on. As we learned in AP biology this year, our bodies contain DNA polymerases that are constantly proofreading our DNA strands to make sure all of our nucleotides are correctly paired. If they are not, they are programmed to cut out the incorrect segment and replace it with the correct nucleotides. We even have a DNA ligase that acts as the glue in our DNA and keeps everything together. If the DNA polymerase were unable to detect the incorrect nucleotide matchup then it would stay and end up as a permanent mutation in the next cell division. Errors with the DNA polymerase, such a tiny part of our whole working body, are alike to the small error in CRISPR technology. The inability to recover all of the genomes due to the tiniest difference will cause scientists to miss out on the reincarnation of animals lost forever. 

Overall, though CRISPR findings are really “awesome”, it may not be the best use of money when we are struggling to keep our rhinos alive. In my opinion, CRISPR is not worth the funding until we are able to figure out how to recover 100% of the extinct genome. Comment your opinion on whether CRISPR should continue to receive additional funding, essentially is it worth it knowing we will never recover 100% of the extinct genome? 

The Dangers of De-Extinction

uploaded by: FunkMonk

Our once ludicrous dream of resurrecting our dead animal friends, like the wooly mammoth, is transforming into a real possibility! According to David Schultz’s article on, due to human advancements made in the study of genetic engineering, scientists at Harvard University were able to reach new heights in the efforts to tackle de-extinction. However, now that it is almost within man’s capability to actually bring back extinct animals, there is a spark of skepticism sweeping the scientific world. “The conversation thus far has been focused on whether or not we can do this. Now, we are progressing toward the: ‘Holy crap, we can—so should we?’ phase,” states ecologist Douglas McCauley. McCauley shines light on the sudden realization of how resurrection may be exciting, yet also very demanding and potentially harmful. Due to tight funds, it is believed that resurrection of one extinct animal can harm the life that is already struggling to be sustained on earth.

In order to reach this financial conclusion, researchers sought out databases in New Zealand, Australia, and New South Wales that are responsible for tracking the cost of conserving endangered animals. With this information from the databases, the researcher team believed that it would cost just as much, if not more, to maintain a resurrected species as it would an endangered species. What this means is, that the already tight funds that conservationists have to support endangered animals would be stretched immensely in order to fund the conservation of a newly resurrected wooly mammoth species, for example. Schultz writes, “The result, the team calculates, would be an overall loss of biodiversity—roughly two species would go extinct for every one that could be revived.” Because of the world’s budget for species preservation, and as author and biologist Joseph Bennet says, “It’s better to spend the money on the living than the dead.”

With that being said, it appears that our excitement around bringing the dead back to life has been faded by the the reality of our world’s finances. Though the study of extinction is still vast, perplexing, and amazing, the application of our resurrecting abilities may not happen anytime soon. Would you like to someday walk on the earth with our old prehistoric animal friends or would you rather save the world’s endangered species first?


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