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Modern Genetic Analysis Chapter 3. Gene Function
Functional Division of Labor in the Gene Set

What different types of genes are needed to construct an organism? No complete answer can be given to this question at the present stage of research, but some idea of the general categories of genes and the relative sizes of these categories is available. The complete nucleotide sequence of the genome of baker's yeast, Saccharomyces cerevisiae, has been obtained (the only eukaryotic genome to be totally sequenced so far). From this complete sequence it has been determined that there are approximately 6340 genes. Of these, 140 code for rRNA, found in a tandem array on chromosome 12; 40 for small nuclear RNA genes scattered throughout the chromosomes; and 275 for tRNA genes (in 45 "families"see Chapter 12). The remaining 5885 genes code for proteins. It is still not known if this proportion of untranslated RNA and protein-coding genes will be typical for all eukaryotes.

The set of protein-coding genes of an organism is called its proteome. Division of labor within the proteome is a topic of considerable interest in understanding what types of genes are needed for an organism to function. From human genes so far studied, the following estimate of the proportion of different protein functions has been made:

Of the enzymes mentioned so far in this text, RNA polymerase and aminoacyl-tRNA synthetase are in the first category. The enzymes controlling the biosynthesis of arginine in Neurospora and those involved in PKU and cystic fibrosis in humans are in the second category.

From a large sequenced portion of the genome of the model plant Arabidopsis thaliana, a tentative view of a plant proteome has been deduced. This is represented diagrammatically in Figure 3-30.

From such estimates, hazy outlines appear of the complete genetic blueprints for life on this planet, including the blueprint for our human species.

© 1999 by W. H. Freeman and Company. All rights reserved.