Reading Passage 1
You should spend about 20 minutes on Questions
1–16 which are based on Reading Passage 1 below.
How bacteria invented gene editing
This week the UK Human Fertilisation and Embryology Authority okayed a proposal to modify human embryos through gene editing. The research,
which will be carried out at the Francis Crick Institute in London, should improve our understanding of human development. It will also
undoubtedly attract controversy - particularly with claims that manipulating embryonic genomes is a first step towards designer babies.
Those concerns shouldn't be ignored. After all, gene editing of the kind that will soon be undertaken at the Francis Crick Institute doesn't
occur naturally in humans or other animals.
It is, however, a lot more common in nature than you might think, and it's been going on for a surprisingly long time - revelations that have
challenged what biologists thought they knew about the way evolution works. We're talking here about one particular gene editing technique
called CRISPR-Cas, or just CRISPR. It's relatively fast, cheap and easy to edit genes with CRISPR - factors that explain why the technique has
exploded in popularity in the last few years. But CRISPR wasn't dreamed up from scratch in a laboratory. This gene editing tool actually evolved
in single-celled microbes.
CRISPR went unnoticed by biologists for decades. It was only at the tail end of the 1980s that researchers studying Escherichia coli noticed that
there were some odd repetitive sequences at the end of one of the bacterial genes. Later, these sequences would be named Clustered Regularly
Interspaced Short Palindromic Repeats - CRISPRs. For several years the significance of these CRISPRs was a mystery, even when researchers noticed
that they were always separated from one another by equally odd 'spacer' gene sequences.
Then, a little over a decade ago, scientists made an important discovery. Those 'spacer' sequences look odd because they aren't bacterial in
origin. Many are actually snippets of DNA from viruses that are known to attack bacteria. In 2005, three research groups independently reached
the same conclusion: CRISPR and its associated genetic sequences were acting as a bacterial immune system. In simple terms, this is how it works.
A bacterial cell generates special proteins from genes associated with the CRISPR repeats (these are called CRISPR associated - Cas - proteins).
If a virus invades the cell, these Cas proteins bind to the viral DNA and help cut out a chunk. Then, that chunk of viral DNA gets carried back
to the bacterial cell's genome where it is inserted - becoming a spacer. From now on, the bacterial cell can use the space particular virus and
attack it more effectively.
These findings were a revelation. Geneticists quickly realised that the CRISPR system effectively involves microbes deliberately editing their own
genomes - suggesting the system could form the basis of a brand new type of genetic engineering technology. They worked out the mechanics of the
CRISPR system and got it working in their lab experiments. It was a breakthrough that paved the way for this week's announcement by the HFEA.
Exactly who took the key steps to turn CRISPR into a useful genetic tool is, however, the subject of a huge controversy. Perhaps that's inevitable
- credit for developing CRISPR gene editing will probably guarantee both scientific fame and financial wealth.
Beyond these very important practical applications, though, there's another CRISPR story. It's the account of how the discovery of CRISPR has
influenced evolutionary biology. Sometimes overlooked is the fact that it wasn't just geneticists who were excited by CRISPR's discovery - so too
were biologists. They realised CRISPR was evidence of a completely unexpected parallel between the way humans and bacteria fight infections.
We've known for a long time that part of our immune system "learns" about the pathogens it has seen before so it can adapt and fight infections
better in future. Vertebrate animals were thought to be the only organisms with such a sophisticated adaptive immune system. In light of the
discovery of CRISPR, it seemed some bacteria had their own version. In fact, it turned out that lots of bacteria have their own version. At the
last count, the CRISPR adaptive immune system was estimated to be present in about 40% of bacteria. Among the other major group of single-celled
microbes - the archaea - CRISPR is even more common. It's seen in about 90% of them. If it's that common today, CRISPR must have a history
stretching back over millions - possibly even billions - of years. "It's clearly been around for a while," says Darren Griffin at the University
The animal adaptive immune system, then, isn't nearly as unique as we thought. And there's one feature of CRISPR that makes it arguably even
better than our adaptive immune system: CRISPR is heritable. When we are infected by a pathogen, our adaptive immune system learns from the
experience, making our next encounter with that pathogen less of an ordeal. This is why vaccination is so effective: it involves priming us with
a weakened version of a pathogen to train our adaptive immune system. Your children, though, won't benefit from the wealth of experience locked
away in your adaptive immune system. They have to experience an infection - or be vaccinated - first hand before they can learn to deal with a
CRISPR is different. When a microbe with CRISPR is attacked by a virus, the record of the encounter is hardwired into the microbe's DNA as a new
spacer. This is then automatically passed on when the cell divides into daughter cells, which means those daughter cells know how to fight the
virus even before they've seen it. We don't know for sure why the CRISPR adaptive immune system works in a way that seems, at least superficially,
superior to ours. But perhaps our biological complexity is the problem, says Griffin. "In complex organisms any minor [genetic] changes cause
profound effects on the organism," he says. Microbes might be sturdy enough to constantly edit their genomes during their lives and cope with the
consequences - but animals probably aren't. The discovery of this heritable immune system was, however, a biologically astonishing one. It means
that some microbes write their lifetime experiences of their environment into their genome and then pass the information to their offspring – and
that is something that evolutionary biologists did not think happened.
Darwin's theory of evolution is based on the idea that natural selection acts on the naturally occurring random variation in a population. Some
organisms are better adapted to the environment than others, and more likely to survive and reproduce, but this is largely because they just
happened to be born that way. But before Darwin, other scientists had suggested different mechanisms through which evolution might work. One of
the most famous ideas was proposed by a French scientist called Jean-Bapteste Lamarck. He thought organisms actually changed during their life,
acquiring useful new adaptations non-randomly in response to their environmental experiences. They then passed on these changes to their
People often use giraffes to illustrate Lamarck's hypothesis. The idea is that even deep in prehistory, the giraffe's ancestor had a penchant for
leaves at the top of trees. This early giraffe had a relatively short neck, but during its life it spent so much time stretching to reach leaves
that its neck lengthened slightly. The crucial point, said Lamarck, was that this slightly longer neck was somehow inherited by the giraffe's
offspring. These giraffes also stretched to reach high leaves during their lives, meaning their necks lengthened just a little bit more, and so
on. Once Darwin's ideas gained traction, Lamarck's ideas became deeply unpopular. But the CRISPR immune system - in which specific lifetime
experiences of the environment are passed on to the next generation - is one of a tiny handful of natural phenomena that arguably obeys
"The realisation that Lamarckian type of evolution does occur and is common enough, was as startling to biologists as it seems to a layperson,"
says Eugene Koonin at the National Institutes of Health in Bethesda, Maryland, who explored the idea with his colleagues in 2009, and does so
again in a paper due to be published later this year. This isn't to say that all of Lamarck's thoughts on evolution are back in vogue.
"Lamarck had additional ideas that were important to him, such as the inherent drive to perfection that to him was a key feature of evolution,"
says Koonin. No modern evolutionary biologist goes along with that idea. But the discovery of the CRISPR system still implies that evolution
isn't purely the result of Darwinian random natural selection. It can sometimes involve elements of non-random Lamarckism too – a "continuum",
as Koonin puts it. In other words, the CRISPR story has had a profound scientific impact far beyond the doors of the genetic engineering lab.
It truly was a transformative discovery.
Do the following statements agree with the information given in Reading Passage 1?
In boxes 1-5 on your answer sheet, write
True if the statement agrees with the in this
False if the statement contradicts the information
Not Given if there is no information on this
1. The research carried out at the Francis Crick Institute in London is likely to be controversial.
2. Gene editing, like the one in the upcoming research, can happen naturally in humans or other animals.
3. CRISPR-Cas is a gene editing technique.
4. CRISPR was noticed when the researchers saw some odd repetitive sequences at the ends of all bacterial genes
5. A group of American researchers made an important revelation about the CRISPR.
Choose the correct letter, A, B, C or D.
Write your answers in boxes 6–9 on your answer sheet.
6. 'Spacer' sequences look odd because:
A. they are a bacterial immune system
B. they are DNA from viruses
C. they aren't bacterial in origin
D. all of the above
7. The ones, who were excited about the CRISPR's discovery, were:
D. A and B
8. Word "learns" in the line 44, 6th paragraph means:
B. gains awarness
9. What makes CRISPR better than even our adaptive immune system?
A. long history of existence
Complete the sentences below.
NO MORE THAN TWO WORDS from the passage for each answer.
Write your answers in boxes 10-16 on your answer sheet.
10. Vaccination is so effective, because it involves _____________ with a weakened version of a pathogen .
11. CRISPR adaptive immune system works in a way that seems, at least superficially, superior to ours. But perhaps our_____________ is the problem, according to Griffin.
12. Some microbes write their experience into the genome and pass the information to their _____________ .
13. Before Darwin, one of the most famous idea was proposed by a _____________ scientist, Lamarck.
14. _____________ are often used to demonstrate Lamarck's hypothesis.
15. Lamarck's ideas became deeply unpopular as soon as Darwin's ideas _____________ .
16. No _____________ biologist agrees with Lamarck's idea that inherent drive to perfection is the key feature of evolution.