CSB349 - Lecture 3.doc

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Cell and Systems Biology
Alan Moses

CSB349 – Lecture 3 Last lecture: Most of the human genome doesn’t have genes… it has repetitive sequences. Where do genes come from? - 20-25000 genes - Gene duplication and divergence: duplicate the gene and make small changes in it to create new sequences/function Gene duplication: our genes use the same the same mechanisms to duplicate as the repeat sequences do (reverse transcription, etc). Gene Duplication and Divergence: A gene is transcribed into RNA, which can then be converted back to a DNA sequence via reverse transcription to produce a new and different copy of the DNA which is then inserted into the genome. The new copy may have the same function and it may not! Tandem Duplication results in another copy of the DNA sequence right beside the original one. This can result in: - Subfunctionalization: the two genes divide up the function of the ancestral gene - The genes stay similar - One copy degrades - Neofunctionalization: one copy gets a diff function Example: haemoglobin: there used to only one ancestral gene but now there are diff copies (fetal, embryonic, adult) and all have dramatic differences in their expression patterns Example: distal less gene: diff numbers of sequences are present in diff animals and all have diff expressions patterns. Some are expressed in forebrain, some in neural crest etc. Why are the expression of similar genes different? Beca
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