Tag Archives: DNA

Science Saturdays: Differences in DNA – what makes you, you?

In May, Birkbeck’s School of Science held ‘Science Saturdays’, a programme of free online talks every Saturday, open to a global audience. In this blog, Maria Pitharouli, Birkbeck and UCL PhD student, gives her account of the talk she attended by Dr Emma Meaburn, Reader in Human Genetics, about DNA and its role in shaping each person’s development, behaviours, and health.

‘What makes us who we are?’, is a question that has occupied Dr Emma Meaburn since she was a teenager and it is what led her towards becoming a Behavioural Geneticist, as she explained in her recent talk.

Behavioural genetics is focused on the influence of nature (our genes) and nurture (the environment we are exposed to during our lives) on the differences we can observe or measure amongst people. But to understand the effect of nature and nurture we need to understand first what DNA is and how big a role it plays in our day-to-day lives.

The human genome is contained in the nucleus of every cell in our bodies, and it is the complete set of genetic instructions: a sequence of approximately 3 billion of the DNA bases adenine (A), cytosine (C), guanine (G) and thymine (T). Each cell has two copies of these genetic instructions, one inherited from the mother and one from the father. Most of the genetic code is identical amongst humans and follows a specific order. Dr Meaburn talked about why this similarity in the genetic code between people is so important; the sequence of A’s, C’s, G’s and T’s acts as a guide for our cells so they can function properly and create all the components needed to sustain life.

Image 1. The letter “V” indicates the genetic variants scattered throughout the human genome. Source: Polygenic Risk Scores (genome.gov)

However, despite this similarity there are parts of the DNA code that differ between people, called genetic variants (image 1), and they are scattered throughout the human genome. These DNA differences are what really interests Dr Meaburn as they might explain some of the variation in how we think, feel, and act, or why some of us develop health conditions. In the talk, Dr Meaburn described how behavioural genetic research has shown that there isn’t a single gene (or DNA difference) that can explain differences in human intelligence, personality, or susceptibly to mental health conditions such as depression. These complex (or multifactorial) traits and disorders are the result of lots (and lots!) of common genetic variants in combination with our different life experiences.

The talk then described a method called genome-wide association studies (or ‘GWAS’) that have been hugely successful in identifying the specific DNA differences that relate to complex human behaviours and traits.  The GWAS approach requires very large numbers of research participants – typically tens of thousands of people – who donate both DNA and information about their health and behaviours. Interestingly, while GWAS have identified many of the genetic variants that contribute to differences in human health and behaviour, Dr Meaburn emphasised that each of the variants found explains just a tiny amount of the differences we see amongst people. As a result, we now know that complex mental health conditions such as depression are polygenic; any single genetic variant does not cause the disorder, rather many of them together can increase or decrease one’s predisposition to depression.

Dr Meaburn went on to describe how polygenic scores – the sum of the effect of all genetic variants that can either increase or decrease risk to develop a disorder – could potentially be useful for identifying individuals more (or less) susceptible to a wide range of human behaviours or health outcomes (image 2).  However, it is important to keep in mind that polygenic scores will never be a ‘crystal ball’, as while DNA differences are important, we know that our environment and life experiences matter too.

Image 2. Polygenic scores can help us identify someone’s genetic likelihood to develop a specific disorder or trait. Source: Polygenic Risk Scores (genome.gov)

The take home message from the talk is that the DNA sequence you have inherited from your parents is an important piece of the puzzle in explaining what makes you, you. Your own unique DNA code plays a role in shaping your development and nudging your health in certain directions.  In the last ten years GWAS research has shown us which DNA variants are important, and the real challenge for the next ten years is understanding how they lead to differences between us in how our brains work, and how we interact with others and the wider world around us.

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Life Story: The Race for the Double Helix

This post was contributed by Professor Nick Keep, Executive Dean of the School of Science. Professor Keep attended the Birkbeck Science Week 2016 film screening of “Life Story: The Race for the Double Helix” on Monday April 11 at the Birkbeck Cinema.


“Life Story: the race for the Double Helix”is a 1987 BAFTA award winning film length TV dramatisation of the story of the discovery of the structure of DNA. The film screening was co-introduced by Dr Richard Hamblyn from the Dept of English and Humanities, who works at the interface of science and literature, and Dr Tracey Barrett from the Dept Biological Sciences, a female protein crystallographer in a Birkbeck tradition that goes back to Rosalind Franklin.

Richard described the film as having two classic odd couples; Crick and Watson in a glossy tourist Cambridge, and Wilkins and Franklin in a rainy London, contrasting with Franklin’s former sunny life in Paris and the easy going relationship with her previous collaborator Vittorio Luzzati, the inventor of the Luzzati plot.

The search for truth in science

Tracey outlined the importance of the science and the changes for women in Science. There are no longer men-only common rooms, such as Franklin encountered at Kings, but there are still problems. They also discussed the interplay between the search for truth in science and competition to be first and famous. Birkbeck is mentioned in the film as the place of refuge Franklin can relocate to escape the oppressive atmosphere at Kings. Richard quoted Rosalind Franklin as writing that she “will be moving from a palace” (Kings) “to a slum” (Birkbeck)” but I’m sure I will find Birkbeck pleasanter all the same”.

The film itself was excellent with Juliet Stevenson as Franklin, Alan Howard as Wilkins, Tim Piggot-Smith as Crick and Jeff Goldblum as the ambitious Watson. I found Clive Panto very convincing (if a little overweight) as Max Perutz, the only character that I knew in person, albeit later in his life. The widespread smoking was an authentic period touch that stood out for me. Whether a 2017 production would do that I am not sure.

Discussing the injustice

The Race for the Double Helix.jpg

By Source, Fair use, https://en.wikipedia.org/w/index.php?curid=46189683

After the showing, the audience discussed the injustice of Rosalind Franklin not winning the Nobel Prize. Firstly the prize is never awarded to more than three people so a decision had to be made and by this time Rosalind Franklin had tragically died. Interestingly, checking afterwards, the ban on posthumous prizes was only formalised in 1974, well after the 1962 award for DNA (See section on Posthumous Nobel Prizes), although observed in practice for Science awards until it was discovered that one of the 2011 winners for Physiology and Medicine had died three days before the announcement, but this was not known to the Swedish Academy when they released the names.

The 1961 Peace prize, just a year before the Medicine and Physiology award to Crick, Watson and Wilkins, was knowingly awarded to the UN Secretary General, Dag Hammarskjöld, who had recently died in an air crash, as was the 1931 Literature Prize to a Swedish Poet. Whether Rosalind Franklin is better known now for not having been awarded the Nobel Prize, than she would have been if she had received it is a matter for debate. Birkbeck, where she worked at the end of her life, remembers her via the Rosalind Franklin Laboratory built in 1996 and, from this year, the annual Rosalind Franklin lecture by a leading woman scientist in a field Birkbeck researches in.

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Redesigning Biology. Birkbeck Science Week 2014

This post was contributed by Dr Clare Sansom, Senior Associate Lecturer in Birkbeck’s Department of Biological Sciences

Dr Vitor Pinheiro (right) and Professor Nicholas Keep, Dean of the School of Science

Dr Vitor Pinheiro (right) and Professor Nicholas Keep, Dean of the School of Science

The first of two Science Week talks on Wednesday 2 July was given by one of the newest lecturers in the Department of Biological Sciences, Dr Vitor Pinheiro. Dr Pinheiro holds a joint appointment between Birkbeck and University College London, researching and teaching in the new discipline of synthetic biology. In his talk, he explained how it is becoming possible to re-design the chemical basis of molecular biology and discussed a potential application of this technology in preventing contamination of the natural environment by genetically modified organisms.

Synthetic biology is a novel approach that turns conventional ways of doing biology upside down. Biologists are used to a “reductionist” approach to their subject, breaking complex systems down into, for example, their constituent genes and proteins in order to understand them. In contrast, synthetic biology is more like engineering, a “bottom-up” approach that tries to assemble biological systems from their parts. Pinheiro introduced this concept using a quotation from the famous US physicist Richard Feynman: “What I cannot create, I cannot understand”. Synthetic biologists often use vocabulary that is more characteristic of engineers or computer scientists: words like “modules”, “device” and “chassis”.

All life on Earth is dependent on nucleic acids and proteins; the former store and carry genetic information, and the latter are the “workhorses” of cells. They are linked through the Central Dogma of Molecular Biology which states, put somewhat simplistically, that “DNA makes RNA makes protein”. The information that goes to make up the complexity of cells and organisms is held in DNA and “translated” into the functional molecules, the proteins, via its intermediate, RNA. The mechanism through which the biology we see now arose – evolution – is well enough understood, but it is not yet clear whether evolution had to create the biology we see today or if it is a kind of “frozen accident”. There is, after all, only one “biology” for us to observe. But synthetic biologists are trying to build something different.

DNA is made up from three chemical components and structured like a ladder: the rungs are made up of the bases that contain the information, and sugar rings and phosphate groups make up the steps. All three components can be chemically modified, affecting the physical properties and the potential for information storage of the resulting nucleic acid. Any modifications that do not disrupt the natural base-pairing seen in DNA and RNA can be exploited to make a nucleic acid that can exchange information with nature. And if the enzymes that in nature replicate DNA or synthesise RNA can also be exploited to synthesise and replicate these modified nucleic acids, that process will be substantially more efficient than chemical replication. Modification of different components presents different re-engineering challenges and different potential advantages. Sugar modifications are not common in biology and are expected to be harder than nucleobases to engineer. On the other hand, they are expected to increase the resistance to biological degradation of the modified nucleic acid. These synthetic nucleic acids have been generically termed “XNA”.

Pinheiro, as part of a European consortium, led the development of synthetic nucleic acid in which the natural five-membered sugar rings had been replaced by six-membered ones. They are more resistant than DNA to chemical and biological breakdown, and have low toxicity, but are poor substrates for the polymerases that catalyse DNA replication and RNA synthesis. Further, he has harnessed the power of evolution to create “XNA polymerases” through a process called directed evolution. In this, hundreds of millions of variant polymerases are created and those that happen to be better able to synthesise the selected XNA are isolated. The process is repeated until the best polymerases are identified or isolated polymerases have the required activity.

These synthetic nucleic acids, however, still cannot be involved in cell metabolism and this is a current research bottleneck that prevents the development of XNA systems in bacterial cells. An alternative route towards redesigning biology would be to modify how information stored in DNA and RNA is converted to proteins: redesigning and replacing the genetic code. The exquisite fidelity of the genetic code depends on another set of enzymes, tRNA synthetases, which connect each amino acid to a small “transfer” RNA molecule including its corresponding three-base sequence or codon. This allows the amino acid to be incorporated into the right place in a growing protein chain. In nature, almost all organisms use the same genetic code. Synthetic biologists, however, are now able to build in subtle changes so that, for example, a codon that in nature signals a stop to protein synthesis is linked to an amino acid, or one that is rarely used by a particular species is linked to an amino acid that is not part of the normal genetic code.

Any organism that has had its molecular biology “re-written” using XNA and non-standard genetic codes should be completely unable to exchange its information with naturally occurring organisms, and, therefore, would not be able to flourish or divide outside a contained environment: it could be described as being contained within a “firewall”.  It would therefore lack the risks that are associated with more conventionally genetically modified organisms: that it might compete with naturally occurring organisms for an ecological niche, or that modified genetic material might spread to them. If, or more likely when, these “genetically re-coded organisms” are released into the environment (perhaps to remove or neutralise pollutants) they will not be able to establish themselves in a natural ecological niche and will therefore pose negligible long-term risk. The more such organisms deviate from “normal” biology, the safer they will become.