We discuss it here with emphasis on how these mechanisms operate in development. Differentiation clearly involves differential gene expression, that is, the expression of different genes in different types of cells. In subsequent lectures we will explore in some detail the mechanisms of control at several of these levels. First, however, we will briefly discuss the genome as a whole, in terms of its size, information content, organization, and constancy during development. However, note that genome size is not necessarily a measure of biologically relevant information content.
Genome complexity is a better measure of at least the potential information content of the genome.
Note that genome complexity is still not necessarily a measure of biologically relevant information content. Note that for metazoans, particularly vertebrates, the percentage of DNA complexity that represents coding sequences of genes is very small. Much better estimates for number of genes are beginning to come from sequencing entire genomes and using computer analysis to identify active genes from their sequence characteristics. Based on recent estimates from genomic sequencing. A partial answer comes from considering the sequence elements in a typical gene.