3.1 Genes

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Chris Paine’s BioKnowledgy presentation – very complete: http://www.slideshare.net/diverzippy/bioknowledgy-31-genes


READING – from Biology in Context for Cambridge International A Level, Glenn and usan Toole, 2013, Nelson Thornes

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READING – from Biology for the IB Diploma Second Edition, C.J. Clegg, 2014, Hodder Education

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THE HUMAN GENOME PROJECT

The HGP was an international attempt to map the entire base sequence of the human genome, including the 1% which constitutes coding genes, the 8% regulatory sequences and the remainder, not all of which has clear functions . The project launched in 1990, funded by the US government and comprising an the international consortium of geneticists from the United Kingdom, France, Australia, China and several other collaborators. The HGP was officially completed in 2003 but not after some controversy caused by a privately funded attempt to unravel the genome, using different sequencing technology, with the intention of commercially capitalising on their results. This research was run by Craig Venter and his company Celera Genomics, but once President Clinton declared that the human genome and its information could not be patented, Venter collaborated with the HGP.

This powerpoint is some years old now and has a special focus upon ethical issues but the presentation is good; it is understandable; and it suffices! human-genome-project-ppt

The Nature of Science focus is upon gene sequencing and how the technology has so dramatically developed, and continues to develop, meaning that sequencing a genome can now be completed in as little as two days. In 1975 Sanger provided the first truly viable sequencing technique, from which were developed the automated techniques which assisted the HGP and Craig Venter. These techniques have now been well overtaken by the so-called ‘next-gen’ techniques which enable extremely rapid sequencing. 

Genomes of a staggering number of species have now been sequenced and analysed. Some interesting comparisons and insights have emerged:genomes-different-species


DNA MUTATIONS AND SICKLE CELLED ANAEMIA

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UPDATE 2nd March 2017: Here is a link to a BBC summary about the way in which, for the very first time, gene therapy has been used to ‘correct’ the abnormal mutation which causes sickle celled anaemia. A 13 year old French boy with an advanced condition of sickle celled anaemia had bone marrow removed and genetically modified using a lentivirus, before being reintroduced back into his body, where it has subsequently been producing largely faultless red cells. http://www.bbc.com/news/health-39142971

This hugely successful and significant gene therapy procedure  was described formally March 2nd 2017 in the New England Journal of Medicine (NEJM), from where it cannot be freely accessed. A version of the story with much more detail and science than the BBC version is available from Medscape:  http://www.medscape.com/viewarticle/876505

In the field of gene therapy this procedure is hugely, hugely significant. For some decades now the dream has been that gene therapy will offer ‘wonder’ cures for several genetically inherited diseases but so far, successes have been limited. From the University of Utah’s Genetic Science Learning Center (Learn.Genetics), here is a summary of the more important successes:  http://learn.genetics.utah.edu/content/genetherapy/success/

(Let me plug, yet again, the University of Utah’s Genetic Science Learning Center. A fabulous resource!  http://learn.genetics.utah.edu/)


COMPARISON OF NUMBER OF GENES IN HUMANS WITH OTHER SPECIES

(Note – this is not a comparison of the genome size but is a comparison of the total number of genes which code for proteins. Remember that this coding DNA constitutes just 1% of the genome.)

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COMPARING BASE SEQUENCES IN DIFFERENT SPECIES USING A DATABASE – and much, much more!

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I love the way the new syllabus can bring together different themes, concepts and understandings, through a focus upon one, seemingly small component. An understanding of cytochrome c might bring together and help a comprehension of this lot:

  • protein structure structure (2.4 Proteins & HL 7.3 Translation)
  • function in cell respiration as an electron carrier (8.2 Cell respiration HL)
  • coding gene, CYCS, on chromosome 7 (3.1 Genes & 3.2 Chromosomes)
  • mutations of DNA (1.6 Cell division, 3.1 Genes, 3.4 Inheritance)
  • synthesis of a protein through transcription and translation (2.7 DNA replication, transcription and translation & HL 7.2 Transcription and gene expression & 7.3 Translation)
  • comparing gene sequences in different species to provide support for cladistics and evolutionary arguments (5.1 Evidence for evolution & 5.3 Classification and biodiversity)

What is the specific context? Topic 3.1 – Genes. The IB syllabus suggests that students make a comparison between the amino acid sequences of cytochrome c in different species, using Genbank or some other database. Why cytochrome c? Because this electron carrier in mitochondrial membranes has been studied in depth as molecular evidence for the 3 Domain proposal for the classification of living organisms. Read on …. it is fascinating!

Now comparing amino acid sequences in different species. This is from Biology Second Edition, C.J. Clegg, 2014, Hodder Education and seems to work fine for cytochrome c oxidase, if you follow the instructions and use your head!p-137-gene-bankp-138

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