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DNA – an introduction part 1

DNA - an introduction part 1
There are two introductory matters to be mentioned before we begin. The first is that getting the level right for such a varied audience is not easy. Some of you may well have a postgraduate degree in molecular biology. But others may have had minimal formal science education, and be facing jargon that is much more difficult to deal with than the basic and less technical content covered elsewhere. To the former, we look forward to your contributions to the discussions, where your perspectives should add to understanding of the topics by those with a more basic knowledge level. To the latter, the two recommended introductory texts should help. Please see the course resources, and please ask questions in the discussions.
The participants in the MOOC constitute a powerful learning community which can work to the benefit of everyone. The second is that we are now going to deal with the question of who. The content is focused on DNA technology. And it does not deal with personal identification from the pre-DNA era or from other biometric measurements, such as fingerprints or facial recognition, and only mentions earlier forensic DNA technologies very briefly. Let’s begin with everyday identity.
If you go to a concert, or sporting event, or even a large shopping centre, those around you will all be different– male or female; short or tall; blue eyed or brown eyed; black, brown, red, or blonde hair, and in some cases balding; of varied race; and with different facial features– unless of course we bump into twins, which is highly unlikely, as only around 15 of every 1,000 live births is of twins. If we change the setting to a wedding, everyone will still look different. But the range of characteristics within each family will be smaller. The bride’s family may have several members who have red hair, while the groom’s family may have mainly dark brown hair.
Pretty well everyone today knows that we look the way we do because that’s the blueprint that our DNA laid down to be followed as we grew from an embryo to an adult, and that every blueprint, other than for identical twins, is different. We also know that the elements that make up the blueprint are inherited from our parents, and that some, but not all of them, will be shared by our siblings. The area of scientific knowledge that encompasses our blueprint is called genetics. The field is still advancing, but its modern roots can be traced to the work of Gregor Mendel in the mid-19th century.
Mendel observed that certain traits in pea plants were passed from parent to offspring in discrete units, functionally what we would now call genes. Within a few decades, it was shown that the units of inheritance were located in structures in the cell nucleus called chromosomes. But we had to wait another 50 years to find out the workings of the mechanism of inheritance. This came with the publication of Watson and Crick’s famous paper that showed that DNA in the chromosomes was in the form of a double helix. It took about 10 more years to elucidate how the information contained in the sequence of bases was translated and show that they defined the sequence of amino acids required to synthesise a specific protein.

Previously we suggested that the level of knowledge of the basic sciences that are the basis of forensic biology will probably vary considerably across our participants.

The same applies to the material on DNA. However, it is more complex than the blood basics and we encourage you to be an active learning community here, and use the discussion board for Q&A sessions on DNA, where those in the ‘know’ can help those who may find the material more complicated. Don’t be afraid to ask questions!!!

Forensic DNA is all about ‘Who?’ and the video begins with a discussion of what we mean by identity and how genetics makes us individual. Make sure that you have viewed and understood the content of the YouTube videos in the DNA basics and glossary section on the previous step. You might need to review these videos a number of times to help your understanding.

Finally, there is a PDF ‘Forensic DNA summary-the main points’ in the ‘Downloads’ resource section at the bottom of the page which provides the key points that you should know about the subject on completion of this week.

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Introduction to Forensic Science

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