3.2 Chromosomes

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SYLLABUS CONTENT

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APPLICATIONS AND SKILLS3-2-applications-and-skills

An introduction, from: Glenn and Susan Toole, Biology in Context for Cambridge International A Level, 2013 Nelson Thornes. (These two pages in no way are designed to work with the IB syllabus but do serve as a starter.)toole-p-68toole-p-69

Specific to the IB syllabus (incl. NoS) from: C.J. Clegg, Biology for the IB Diploma Second Edition, 2014, Hodder Education)

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CHROMOSOME STRUCTURE

The SL/Core syllabus does not demand much about chromosome structure. A comparison between prokaryotic and eukaryotic DNA leads to the idea of chromosomes in eukaryotic organisms, consisting of about 60-70% histone protein which provides the frame around which the DNA can be wound and condensed into a smaller structure. They say that if human DNA was not condensed in this way and all your DNA was lined out end to end, it would stretch at least once all around the planet! maxresdefault

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(NoS) AUTORADIOGRAPHY AND THE LENGTH OF DNA

The focus here is to show how advances in scientific techniques, in this case, autoradiography, help move scientific knowledge and understanding ahead. John Cairns, a British biochemist, and the ‘Cairns Technique’, which significantly helped move forward an understanding of DNA: https://www.youtube.com/watch?v=UHnxiF6qzhI

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KARYOGRAMS AND KARYOTYPING – Sex and Down’s Syndrome

This IB syllabus focusses upon karyograms to determine sex and Down’s Syndrome.

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Here are some normal, male and female karyograms, derived from randomly pictured chromosomes. Notice how, in the karyograms, the chromosomes are paired in lessening order of size.

There are lots and lots of neat karyotyping activities out there. Here’s a class assignment from Prentice Hall’s Biology Laboratory manual, which I have adapted and use:

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