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MCDB 4650 DEVELOPMENTAL BIOLOGY CLASS NOTES Class 2 2 - 1 Genomic information content and constancy; Developmental regulation of gene expression Reading : Most of this, if not all, should hopefully be review from molecular biology. Chp 4: 86-92, Chp 5: 101-113, 116-119, 125-128, 130-132, 137. Another good and detailed source, if you feel you need more, is Alberts 4th edition – see link on web page. Learning goals : Be able to: Estimate and compare the information content of different genomes. Define differential gene expression and its relationship to differentiation. Describe the control points in gene expression at which synthesis of the active protein gene product can be regulated. Explain what is meant by and the significance of combinatorial controls in the regulation of gene expression during development. Genomics: the information content of animal genomes How much information does it take to make a worm? To make a human? And how can we estimate information content? Is the information all in coding genes? Genome size doesn’t matter. The number of nucleotide pairs per haploid set of chromosomes varies over a 1000-fold range among higher organisms, with no clear correlation to biological complexity or perceived evolutionary sophistication. Genome complexity , the total length of non-repeated sequences in the genome (that is, sequences present more than once are counted only once) seems to correlate better (Table 1). Number of functional genes can now be estimated from genomic sequences, using computer analysis to distinguish genes from non-coding sequence (how?), and the results are surprising. Is it possible that we have in our human genomes only twice the information necessary to make a lowly nematode worm? Does the last column gives a clue to what may be going on. What does it mean? Genome complexities and estimated numbers of genes for various organisms Organism Complexity (Mb) Estimated Genes Percentage non-Coding* E. coli 5 4,000 ~ 20% Yeast 10 5,000 ~ 50% Caenorhabditis 97 19,000 ~ 80% Drosophila 180 13,000 ~ 92% Human 3,000 ~40,000 ~ 99% * Based on 1,000 bp as the average length of coding sequence per gene. All organisms have a substantial amount of non-coding DNA (introns, spacer sequences, regulatory sequences, untranslated RNAs, etc). What is it for? It seems likely that at least some non-coding DNA has no essential functional importance: the pufferfish, a quite respectable vertebrate, has evolved a streamlined genome of only 400 Mb by eliminating intron and many intergenic sequences. However, the regulatory sequences, transposons, micro RNAs, etc., all clearly serve important regulatory roles. Are changes in DNA sequence information developmentally important? Most organisms don't undergo much if any loss or alteration of DNA sequences, based on a variety of
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This note was uploaded on 02/25/2010 for the course MCDB 4650 taught by Professor Staff during the Spring '08 term at Colorado.

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