3.5 Genetic modification and biotechnology

Assessing risks associated with scientific research—scientists attempt to assess the risks associated with genetically modified crops or livestock.

Genetically Modified Organisms is a great topic to encourage deeper thinking and to have students consider the impacts of science on society. There is a lot of genuine mistrust and concern with this, but there is also a lot of misinformation and misunderstanding of the science, so it makes a good topic to link to the importance of scientific literacy.

I like to use the different thinking routines created by Project Zero for Visible Thinking and have written about them before when discussing stem cells. For GMOs, we used the Circle of Viewpoints to try to understand the many perspectives on this topic.

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Circle of Viewpoints – Visible Thinking

We came up with a great range of viewpoints:

  • A concerned parent/consumer
  • An FDA spokesperson
  • A worker at Monsanto
  • A large-scale commercial farmer in the US
  • A small-scale organic farmer in the US
  • A subsistence farmer in Cambodia
  • A Greenpeace activist
  • A UN worker
  • the Pope
  • an ecologist
  • a member of the Just Label It coalition

It was a really useful exercise and the students tried to get under the skin of their characters! It helped the students identify the range of viewpoints and we were able to narrow down to some of the key concerns about the technology. To guide our discussion we focused principally on three examples of GMOs: Bt Cotton, Golden Rice and the recently approved AquaAdvantage GM Salmon. The risks we discussed included: possible health concerns/allergies; the risk of genetic contamination of wild organisms; increasing the evolution of Bt resistant pests and risks to non-target species. The role-play allowed us to balance these risks with the possible increases in yield and efficiency, nutritional benefits and less use of pesticides. The issues of labelling and the possible (emotional?) response we have to knowing that the food is GMO could provide the basis for a good TOK lesson as well. We also discussed the extensive testing that the GM salmon has been forced to undergo and that it has been nearly 20 years of research and development – at what point should we accept that something is low-risk? When do we decide that we have sufficient evidence in the natural sciences to support a conclusion?

The main challenge we found was placing a time limit on the discussion, as we could comfortably have debated this for several more lessons.

 

“Circle Of Viewpoints | Project Zero”. Pz.harvard.edu. N. p., 2016. Web. 15 Aug. 2016.

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Best Holiday Read 2016

Like all good biology teachers, I try to load up my summer reading list with the latest science books.  One book in particular stands out this year and I think it deserves its own blog post!  Described as a “biography of the gene”, The Gene by Siddhartha Mukherjee is a phenomenal book.  Beautifully written (the author, a cancer physician and researcher, has a genuine literary touch) it is a fascinating overview of our understanding of the gene.  It takes us from the first Aristotelian musings on inheritance all the way forward to today’s latest insights into genetics and molecular biology.  All the famous geneticists from the Nature of Science are in here: Mendel, Darwin, Morgan , Watson, Crick, Franklin, Sanger and too many more to list.  In fact, the book is the perfect compendium for IB Biology students!  The narrative is lively and engaging and the individual personalities of the scientists leap off the page. It is worth making time for, even in the busy schedule of an IB student.

the-gene-9781476733500_lg

3.4 Inheritance

Making quantitative measurements with replicates to ensure reliability. Mendel’s genetic crosses with pea plants generated numerical data.

Gregor Mendel, the “Father of Genetics”, made his discoveries on inheritance by using the garden pea, Pisum sativum. Mendel’s experiments and data collection over eight years formed the foundation of theoretical genetics and were able to be used in diagnosing and explaining genetic diseases at the turn of he 20th-century.  Just as important as his discoveries, though, was his meticulous following of the scientific methods, illustrating perfectly that replicates in quantitative experiments allow for greater reliability in the conclusions.

peas
The seven traits Mendel studied (Griffiths et al.)

Mendel worked with the seven traits outlined above and bred them for two years to establish pure, or homozygous, breeding strains. He then pollinated the parental flowers that showed variation in the trait – for example, crossing purple flowers with white flowers.  This produced in the F1 generation 100% purple flowers.  When these flowers were self-pollinated, Mendel noticed a curious relationship in the F2 offspring: a ratio of almost exactly 3:1 in the phenotype.

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The data of the F2 ratio from Mendel’s experiments, a total of over   18, 000 breeding experiments. (Griffiths et al.)

On the basis of this data, Mendel was able to draw key conclusions about the nature of inheritance.  These were:

  1. The existence of what we now know as genes.
  2. That these genes come in pairs
  3. Gene pairs segregate during the production of gametes
  4. Each gamete thus only contains one gene of a pair.
  5. Fertilisation is random

These statements were able to be tested by a new round of experiments, because they were based on quantitative data, had significant repetition and suggested certain patterns in inheritance.  His subsequent experiments provided confirmation of his analysis.  Not bad, considering the structure of DNA wouldn’t be determined for another century!

Mendel also did some interesting work on dihybrids, but that’s for a later topic!

Sources:

Griffiths AJF, Miller JH, Suzuki DT, et al. An Introduction to Genetic Analysis. 7th edition. New York: W. H. Freeman; 2000. Mendel’s experiments. Web. May 2, 2016.

Miko, I. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. 2008. Web. May 2, 2016.

3.1 Genes, 3.2 Chromosomes and Technology

3.1 Developments in scientific research follow improvements in technology—gene sequencers are used for the sequencing of genes.

3.2 Developments in research follow improvements in techniques—autoradiography was used to establish the length of DNA molecules in chromosomes.

Perhaps no other area of biology has benefited so greatly from technological advances than genetics. Our knowledge and understanding of inheritance has increased dramatically over the last 50 years as technology had allowed us to delve ever deeper into the mysteries of our genes and our evolution.

The Gene Sequencer has made possible the ability to determine the order of As, Ts, Cs and Gs in any genome and was essential to decoding the Human Genome Project.  The breakthrough Sanger Sequencing technique from 1975 has been adapted and updated to provide rapid and inexpensive gene sequencing information. There is a good overview of how they work at the Scitable Page, including a short video.  There are strong links to the process of DNA replication; in fact, the method of gene sequencing relies on manipulating replication. It is worth remembering, however, that sequencing only allows us to see the sequence of bases, it does not tell us about the genes themselves.  Thus sequencing is only the first step in understanding how the genome functions.

On a smaller scale, but no less important, was John Cairns’ breakthrough in 1963 using autoradiography.  Using radioactively labelled thymidine (the nucleoside using thiamine as its base) he examined bacterial DNA during and after DNA replication.  After the the radioactive bases were incorporated into the cells, he lysed them and then prepared slides using X-ray film.  They took two months to develop! This technique is known as Autoradiography. It was used by the Curies for some of their work on radioactivity, but its use for biological purposes really became apparent after World War 2, when it was used extensively to investigate RNA and DNA.

Cairns was able to interpret his images as providing evidence of the bacterial circular chromosome and of showing the movement of the replication fork around the chromosome.

The circular bacterial chromosome. (Griffiths AJF, Miller JH, Suzuki DT, et al. 2000)
The circular bacterial chromosome. (Griffiths AJF, Miller JH, Suzuki DT, et al. 2000)
The spreading replication fork around the circular chromosome. (Griffiths AJF, Miller JH, Suzuki DT, et al. 2000)
The spreading replication fork around the circular chromosome.
(Griffiths AJF, Miller JH, Suzuki DT, et al. 2000)

The autoradiographs also allowed the first estimates of chromosomal length.   By measuring the lengths of the radiated bases within the chromosome, an estimate could be  achieved; in this 1100 µm.

When newer and more advanced technologies are invented, what will change about our understanding of the world? What do we hold true today that might turn out to be false tomorrow? To what extent is knowledge fixed in the natural sciences?

References

Adams, J. (2008) DNA sequencing technologies. Nature Education 1(1):193  http://www.nature.com/scitable/nated/article?action=showContentInPopup&contentPK=690

Cairns, J. 1980. The bacterial chromosome and its manner of replication as seen by autoradiography. Current Contents: Life Sciences. (29): 20-20. http://www.garfield.library.upenn.edu/classics1980/A1980JY54900001.pdf#search=%22John%20Cairns%20DNA%22

Griffiths AJF, Miller JH, Suzuki DT, et al. An Introduction to Genetic Analysis. 7th edition. New York: W. H. Freeman; 2000. Replication of DNA. Available from: http://www.ncbi.nlm.nih.gov/books/NBK21790/

Griswold, A. (2008) Genome packaging in prokaryotes: the circular chromosome of E. coli. Nature Education 1(1):57

3.3 Meiosis, 10.1 Gene Linkage and 10.2 Inheritance

Making careful observations—meiosis was discovered by microscope examination of dividing germ-line cells. (3.3 – Core)

Making careful observations—careful observation and record keeping turned up anomalous data that Mendel’s law of independent assortment could not account for. Thomas Hunt Morgan developed the notion of linked genes to account for the anomalies.  (10.1 – AHL)

Looking for patterns, trends and discrepancies—Mendel used observations of the natural world to find and explain patterns and trends. Since then, scientists have looked for discrepancies and asked questions based on further observations to show exceptions to the rules. For example, Morgan discovered non-Mendelian ratios in his experiments with Drosophila. (10.2 – AHL)

Both core and HL topics on meiosis focus on the importance of making observations and accurately interpreting them.  The HL NOS, with its references to Morgan, illustrates how this process helps expand and redefine our understanding of biology. Morgan is an interesting character and worth spending some class time on.

When Mendel’s genetic studies were rediscovered, scientists set about replicating and confirming them. However, one group (William Bateson, Edith Rebecca Saunders, and Reginald Punnett, he of the eponymous square) persistently found phenotypic ratios that were far more common than could be predicted based on Mendelian inheritance patterns. Examining pea plants during a dihybrid cross (link to AHL Topic 10.2), they received statistically significant deviations from the predicted, as seen below:

Characteristics of the F2 Generation (Bateson et al., 1905)
Characteristics of the F2 Generation (Bateson et al., 1905)

They surmised that the alleles must be coupled somehow, but could not explain how.  Enter Professor Thomas Hunt Morgan.  Five years later, 1910, he was experimenting on fruit flies, Drosophila melanogaster, and found a white-eyed male in one of his studies (fruit flies normally have red eyes). Further experimentation found that instead of an expected 1:1:1:1 ratio of red-eyed females, red-eyed males, white-eyed males, and white-eyed females, he observed the following phenotypes in his F2 generation: 2,459 red-eyed females, 1,011 red-eyed males and 782 white-eyed males. The lack of white-eyed females led him to hypothesise that the gene must be linked to the sex factor.  This later led to the concept of gene linkage: genes on the same chromosome do not assort independently.

Columbia University Fly Room - note bunches of bananas! © 2013 The American Philosophical Society
Columbia University Fly Room – note bunches of bananas!
© 2013 The American Philosophical Society

This was groundbreaking – it meant that genes were concrete, real objects that could be located on chromosomes  and their inheritance and behaviour mapped, predicted and analysed. Interestingly enough, Morgan had initially rejected the idea that genes were located on chromosomes, believing that data generated through passive observation could not be trusted; another instance of scientists having to reject old ideas in favour of new and compelling evidence. Morgan would go on to win the Nobel Prize in Physiology or Medicine  “for his discoveries concerning the role played by the chromosome in heredity” (Nobelprize.org; 2014).

We will discussing a lot more about Prof. Morgan in our next unit, Inheritance.

Extra: One of the prescribed TOK Essay Titles for May 2015 was: “There are only two ways in which humankind can produce knowledge: through passive observation or through active experiment.” To what extent do you agree with this statement?  You could consider drafting a short response using Morgan as a specific example.

References:

Lobo, I. & Shaw, K. (2008) Discovery and types of genetic linkage. Nature Education 1(1):139. Web. 17 Mar 2015.

Miko, I. (2008) Thomas Hunt Morgan and sex linkage. Nature Education 1(1):143. Web. 17 Mar 2015.

“The Nobel Prize in Physiology or Medicine 1933”. Nobelprize.org. Nobel Media AB 2014. Web. 17 Mar 2015.

Images:

Bateson, W., et al. (1905) Characteristics of the F2 Generation. Reports to the Evolution Committee of the Royal Society. Nature Education. Web. 17 Mar 2015.

n.a. (1913). Columbia University Fly Room. The American Philosophical SocietyNature Education. Web. 17 Mar 2015.