Notes for teachers
At a glance
The following activity provides an opportunity to for students to review some of the genetic techniques studied at A level. Beyond theoretical review, this activity engages students with interesting real-life scenarios in which genetic testing has been vital to developing our historical understanding.
Learning Outcomes
· Students use problem solving skills to overcome context based archaeogenetic problems
Each student will need
· Textbook
· Big questions: “What can DNA be used for?”
· Encourage students to share and discuss answers before collating suggestions on the board.
· Encourage students to consider in vivo and in vitro uses of DNA.
· Conclude starter by showing Oxford Sparks animation ‘When did cats arrive in Britain? (see web links below)
· Archaeogenetics is unlikely to be one of the uses of DNA listed by the class and so provides a useful and interesting link for students to review genetic techniques.
· Main activity: DNA and Comparative Techniques
· Hand out student worksheets and ask students to complete independently. Students may need to use their textbooks to complete this.
· Circulate to guide and assist students as well as ensure students remain on task.
· Main activity: Answers
· A – see a textbook example.
· Q – Describe and explain the process of gel electrophoresis, using a step by step guide, as a method for visualising DNA for comparison. Start form the point of DNA collection, finishing with the production of a visible ladder.
· A – Answers should describe the process of using restriction enzymes and explain how cutting at specific restriction sites results in unique fragment patterns. Students should describe the gel set up and explain how DNA is separated (according to size) within the gel. Students should describe a method for visualising the fragments within the gel, either using fluorescent tags or radioactive tags with Southern blotting.
· Q - Outline, again using a step by step guide, a second method comparing DNA
· A - Here students may wish provide descriptions for; microarrays, bioinformatics or DNA hybridisation.
· Q - Compare the advantages and disadvantages of the two methods described above.
· Answer depends on choice of second method but answers are likely to revolve around ease of use, expense and speed.
· Q - A number of genetic techniques isolate and examine only STRs or microsatellites. What are these and what properties do they have that makes them suitable for this role?
· A – STRs are short tandem repeats (2-13 bases repeated many times). They are suitable for DNA analysis as they have consistent loci and so are easy to isolate and amplify using PCR. The number of repeats within STR regions is highly variable and so there is sufficient variation to compare even closely related samples.
· Q - Explain why DNA molecules are influenced by an electric field? Top answers should reference the structure of the molecule.
· A – Phosphate groups within the phosphodiester backbone are polar (negatively charged). This gives the DNA molecule an overall negative charge. Charged objects are influenced by electric fields. DNA is thus ‘pushed’ from the negative terminal to the positive terminal.
· Q - Suggest another biological macromolecule which might also be influenced by an electric field. Explain why with reference to its structure.
· A – Proteins will also be affected by electric fields due to the presence of polar R-groups. Their movement in an electric field is, however, less predictable as the proportion of polar R-groups can vary between proteins.
· Q - Outline the steps of a commonly used technique that can be used to overcome this issue.
· A – Students outline steps of PCR.
· Q - Complete the diagram suggesting the likely results of the domestic cat.
· A – Students should suggest a fragment pattern that shares some fragments with the European Wildcat (due to a recent common ancestor) but include some significant differences (as they are different species). The fragment pattern should show less similarity to the ancient sample than is shown by the European Wildcat.
· Q - Suggest from which species of wildcat the domestic cat has descended? Explain your answer.
· A – African wildcat as the domestic cats shares the most fragments in common with this species
· Q - Suggest which species of wildcat are most distantly related. Explain your choice.
· A – African wildcat and European wildcat as the fragment patterns are the most dissimilar.
· Q - Use the information given to suggest how researchers could use genetic samples from living decedents to prove the identity of the discovered remains as that of Richard III.
· A – Mitochondrial DNA (mtDNA) is a segment of DNA which is passed down in the egg and so is transmitted by a mother to all of her children. Only daughters pass it on and therefore it is copied and passed through the female line with people being related through a female line link being expected to share an identical or near identical mitochondrial DNA type.
Cecily Neville, Richard’s mother, would have passed down her mitochondrial DNA type to all of her children. This means that Richard III and Anne of York inherited the same mtDNA from their mother - and as long as Anne’s daughter(s) had a daughter, who had a daughter (highly likely in an age when eight to ten children was common!) and so on, the mtDNA type (or a near identical type) will have been passed down those lines of descent. Michael Ibsen and Wendy Duldig are two such female-line relatives of Richard III.
Consequently, if the remains found at Greyfriars are indeed Cecily Neville’s son Richard III, the mtDNA present should match that of her great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-grandson Michael Ibsen and her great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great granddaughter, Wendy Duldig.
The Y chromosome has on it the gene which sets an embryo down the path to become a boy. It is therefore only passed down from a father to his son(s) and so on down through the generations. Richard III left no living descendants and so, in order to find male line relatives of Richard who should therefore have the same Y chromosome, it is necessary to travel up the tree to Edward III and then down through John of Gaunt to his male-line descendants, the Somersets. It would be expected that these living male-line relatives of Richard would share an identical or near-identical Y-chromosome type.
· Q - Use Suggest why examining Y-chromosome DNA is less likely to be a reliable source of evidence than studying mtDNA.
· A – False-paternity events, where the biological father is not the person thought to be the father of the child, do occur. Dr King and others have looked at historical false-paternity rates and these are estimated to be at 1-2% per generation meaning that a break in the Y chromosome chain would not come as a surprise if found.
Richard III answer credits: https://www.le.ac.uk/richardiii/science/extractionofdna.html
· Plenary
· Key word bingo comprising of DNA and genetic technique key words.
Web links
www.oxfordsparks.ox.ac.uk/content/when-did-cats-arrive-britain