DEVELOPMENTAL BIOLOGY CLASS NOTES
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Genomic information content and constancy; Developmental regulation of gene expression
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.
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
Explain what is meant by and the significance of
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
Is the information all in coding genes?
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
, 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
* 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