A couple posts ago, I wrote a quick comment about Ian Malcom’s view of human dominion over the planet. In this post, I want to talk about the science of Jurassic World: Dominion, specifically the science that plays a central role in the plot of the movie. Be forewarned: I will be spoiling some of the plot in order to explain the science behind the movie.
Jurassic World: Dominion consists of two plots that turn out to be connected. One plot follows the old characters (Alan Grant, Ellie Sattler, and Ian Malcolm, who were all in the very first Jurassic Park movie) and the second plot follows the new characters (Owen Grady and Claire Dearing, who were first introduced in Jurassic World). Grady and Claire’s plot revolves around rescuing their adopted daughter, Maisie Lockwood, a girl introduced in the previous movie. A significant detail about Maisie is that she is a clone. Maisie and Beta (Beta is the offspring of Blue, the main raptor from the Jurassic World movies) were kidnapped by Biosyn, a genetic engineering company, for unknown reasons, and Owen and Claire spend most of the movie chasing them down.
The other plot revolves around giant locust. Yes, the Jurassic franchise, which has been all about putting dinosaurs in the modern world, switches tracks at the last movie and presents genetically engineered locusts as the main threat of the movie. Don’t get me wrong: dinosaurs still show up quite often in Jurassic World: Dominion, they are just not central to the plot anymore. Swarms of these giant locusts are showing up, devastating crops, all except for crops grown from seeds produced by Biosyn. Ellie Sattler suspects Biosyn of creating the giant locusts, so she elicits the help of Alan Grant to help her uncover Biosyn’s activities. Ian Malcolm becomes their inside man, as he works for Biosyn.
How do these two plots converge? Henry Wu, the recurring geneticist throughout the franchise, is working for Biosyn. He knows that the locusts have the capacity to destroy the world’s food supply, and he is determined to stop it. His plan involves infecting the locusts with genetically engineered viruses that would rewrite the genomes of the locusts, eventually killing them. However, he does not have the technical know-how to create the virus. He needs to study the successful work of rewriting genomes performed by Charlotte Lockwood.
Charlotte Lockwood is the genetic donor and mother of Maisie Lockwood (in other words, Maisie is a clone of Charlotte). It turns out that Charlotte had a genetic defect that ended up killing her. She knew she had this defect and she was able to re-write Maisie’s genome to remove the defect. Henry needed Maisie so that he could read her DNA and learn how Charlotte was able to re-write her genome. Henry also claimed that he needed Beta as a comparison, to see how Maisie’s DNA had been changed.
If it seems odd that Henry Wu needed a raptor’s DNA to compare to a human DNA, his justification was that Blue and Charlotte both created their children (Beta and Maisie, respectively) by themselves: no father was involved in either case. Since they were created by the same process, he could compare the two and see how they differed to find how Charlotte corrected Maisie’s genome.
As I write this all out, it is becoming apparent that there is a lot of backstory to the plot of Jurassic World: Dominion. Hopefully, you were able to follow what I explained. If not, the brief summary is that Maisie is a clone and Beta was produced without a father, and their genomes were to be compared to find out how Maisie’s DNA differed from Beta’s.
Now, aside from the problem that a human and a raptor will naturally have very different genomes, since they are different types of creatures, I noticed another problem with Henry Wu’s plan. His explanation for why Maisie and Beta were similar was appropriately vague: both of their mothers created their offspring “by themselves.” That vagueness glossed over the fact that Maisie and Beta were actually created by very different processes. Let me explain.
A clone is an offspring that is genetically identical to the parent. If you take the parent and the offspring and compare their DNA, they will be identical. We often think of cloning as some sort of science fiction capability, but in fact, there are a number of organisms that can produce clones quite naturally. A classic example found in many biology textbooks is the Hydra. No, not the Hydra, the multi-headed monster from Greek mythology, but the animals that belong to the genus Hydra. Hydra belongs to the phylum Cnidaria, which is the same group that includes jellyfish and anemones. A very simple way to explain a Hydra is to think of a tiny, nearly microscopic anemone. It has a tube-like body with a ring a tentacles around its mouth. Now, Hydra can reproduce sexually, producing sperm and eggs, but they can also reproduce asexually by budding. During budding, a lump grows on the side of the Hydra, and that lump eventually grows into a miniature version of the parent. The offspring then detaches from the parent and goes off on its way.
The bud is made from the same genetic material as the parent: there is no reshuffling or mixing of genes when the cells for the bud are produced. Mitosis is the name for the type of cell division that produces genetically identical cells. Thus, a Hydra bud is produced by mitosis. There is another type of cell division called meiosis. It is used to produce sex cells (the sperm and the egg). Meiosis differs from mitosis because not only are the genes shuffled around a little bit, the number of chromosomes is halved. Then, when an egg and a sperm unite in fertilization, they each contribute half of a genome, creating the full genome of the offspring. Since the genes were shuffled around and the offspring contains genes from two parents, the offspring produced by sexual reproduction will be genetically distinct from both parents.
Going back briefly to the plot of Jurassic World: Dominion, Maisie was produced by artificial cloning, thus her genome was identical to that of Charlotte’s, except for those parts of her genome that Charlotte corrected. Now let us consider Beta.
Henry Wu explained that Blue was able to produce Beta on her own because Blue contained some monitor lizard DNA. He did not use the word, but he was referring to parthenogenesis, which is a method of producing viable eggs without the involvement of a male. A few lizard species are known to be to perform parthenogenesis, including a couple of monitor lizards, most notably, the Komodo dragon.
To illustrate how significant parthenogenesis can be, there are some species of lizards that are completely female. One example is the New Mexico whiptail lizard. Every single New Mexico whiptail you find will be female: there are no males. When one of these lizards becomes mature, she begins laying eggs, which then hatch into viable daughters. In the case of the New Mexico whiptail, their entire reproduction is by parthenogenesis. The case is a little different for the Komodo dragon. The majority of Komodo dragon reproduction is ordinary sexual reproduction. However, in the prolonged absence of males, female Komodo dragons have been observed to lay viable eggs. Thus, Komodo dragons appear to be facultative parthenogens, in the sense that they usually reproduce sexually but can switch to parthenogenesis when necessary.
How does parthenogensis occur? Put in real simple terms, at some point during meiosis, the chromosomes get duplicated. I say “at some point” because there are a few moments during meiosis when duplication may occur, and when it occurs appears to differ from one species to another. The result, though, is the same: while the cells are supposed to have half of the genetic material, they actually get a full compliment of chromosomes. Since it has a full compliment of genes, what should be an unfertilized egg can now behave as a fertilized egg, and the offspring begins growing without any involvement from a father.
Now here is a very important point: meiosis creates genetic diversity before fertilization. When we talk about sexual reproduction, the combining of the genomes of two parents is considered to be the main cause of the genetic reshuffling. However, some reshuffling happens during meiosis before the sperm and egg are even created. This means that every time a female produces an egg, the egg’s genome differs from the mother’s genome and from any other eggs produced previously. They will not vary a whole lot, but there will be some variation. Hence, when parthenogenesis occurs, the offspring will have a slightly varied genome compared to the parent. In short, parthenogenesis is not cloning.
To emphasize that the offspring produced by parthenogenesis are not clones, every Komodo dragon produced by parthenogenesis is a male. Clearly, if a female Komodo dragon is producing males by parthenogenesis, the males cannot be clones of the mother.
Let me explain why Komodo dragon parthenogenesis produces males. Remember how parthenogenesis involves a duplication of chromosomes? During meiosis, the number of chromosomes is halved. While a normal cell has pairs of chromosomes, an egg produced by meiosis has one chromosome from each pair. During parthenogenesis, each egg doubles its chromosomes. It does this by copying the existing chromosomes. Where there used to be half of a pair of chromosomes, the chromosome gets copied, creating a pair of identical chromosomes. Thus, the offspring produced by parthenogenesis has pairs of chromosomes, but each chromosome in the pair is identical to each other.
Like us, Komodo dragons have different sex chromosomes and these determine the sex of the animal. We have X and Y chromosomes: if a fertilized egg has XX, it becomes a female, if it has XY, it becomes a male. However, Komodo dragons differ from this pattern. Their sex chromosomes are called Z and W. If a fertilized egg has ZZ, it becomes a male, and if it has ZW, it becomes a female. Basically, it is just like sex determination in humans, only what makes a male in humans makes a female in Komodo dragons, and vice versa.
Since an offspring produced by parthenogenesis has identical copies of its chromosomes, every offspring produced must have two of the same sex chromosomes. Doubling a Z chromosome produces ZZ, which is a male. Doubling a W produces WW, which is not viable. Thus, all of the offspring Komodo dragons produced by parthenogenesis will be males.
Note that not all lizards use the same sort of sex determination as Komodo dragons do. I talked a little bit about the New Mexico whiptail lizards earlier, which is a species of all female lizards that reproduce by parthenogenesis. Obviously, since they are all females, parthenogenesis produces females in that species. It is likely because New Mexico whiptail lizards use sex determination like humans do: a doubling up of existing chromosomes produces XX or YY. The former is female, the latter is non-viable.
All that talk about sex determination in lizards is just to illustrate a little bit of how parthenogenesis works and to show that offspring produced by parthenogenesis are not clones of the mother. Thus, if we return to the plot of Jurassic World: Dominion, Henry Wu had no reason to compare the genomes of Maisie and Beta. They were not even produced the same way, despite Wu saying that their mothers produced them “by themselves.” That is probably why his explanation was so vague, so that it could sound like Maisie and Beta were produced by the same process even though they were not.
In conclusion, the science behind the plot of Jurassic World: Dominion did not follow any real science at all. Perhaps that is to be expected of a movie franchise rooted in science fiction. However, the original “false science” of Jurassic Park, the cloning of dinosaurs from DNA preserved in amber, was necessary to drive the plot. Without cloned dinosaurs, there would be no Jurassic Park in the first place. Thus, I was willing to suspend my disbelief and accept that science fiction in order to enjoy the story. I think Jurassic World: Dominion is a little different. One of the main draws of the movie was that it brought the old characters and the new characters together. Surely the writers could have done that with a different plot, one that did not require some vague “cloning and parthenogenesis are basically the same” sort of explanation. In other words, the “false science” used in Jurassic World: Dominion wasn’t necessary to drive the story, so I am less willing to suspend my disbelief. Unfortunately, that lack of disbelief helped make Jurassic World: Dominion fail in my mind. What was supposed to be the grand conclusion of a series focused on dinosaurs ended with a threat of giant locusts and unjustified science fantasy.
Thoughts from Steven
Phillip Watts, Kevin Buley, Stephanie Sanderson, Wayne Boardman, Claudio Ciofi, Richard Gibson (2006) “Parthenogenesis in Komodo dragons” Nature 444: 1021-1022. Most of the details I will be presenting about Komodo dragon parthenogenesis comes from this brief communication.