Gene number

There are wide variations in features of individual chromosomes (eg, in gene number per Mb, SNP density, GC content, numbers of transposable elements and CpG islands, recombination rate). 

Figure 5.17 Genetic map of phage T 7, showing gene numbers, approximate sizes, and functions of the gene products.

Organism Genome size [Mbp]/ gene number /% in COCsf Clinical disease or syndrome... 

Claverie JM. Gene number. What if there are only 30,000 human genes Science 2001 291[5507] 1255-1257. 

Roest Croellius H et al. Estimate of human gene number provided by genomewide analysis using Tetradon nigroviridis DNA sequence. Nature Genet 2000 25 235-238. 

Figure 6. Regulation of the subtilisin promoter. Shaded areas refer to the promoter and upstream regions of the subtilisin gene. Numbers above the figure indicate base pairs upstream. Activators are shown above the figure, repressors below. Lines indicate possible regions of the DNA involved in binding the regulatory proteins.

Bentley, D.L. Rabbitts, T.H. (1981). Human VK immunoglobulin gene number implications for the origin of antibody diversity. Cell 24,613-623. 

Bird AP. Gene number, noise reduction and biological complexity. Trends Genet 1995 11 94-100. 

COMPARISON OF GENE NUMBERS AND DNA FROM DIFFERENT SPECIES... 

The specific-locus test is not intended for human risk estimation. The seven loci sampled may not be representative of the whole genome. To continue the example of the appendix to this chapter, a mutation rate of 0.000003 per seven loci corresponds to 0.009 for 20,000 loci, if this is taken as the haploid gene number. This is nearly 1% per zygote, not a negligible number. It would be desirable to have methods to measure mutations in the entire genome, or in an entire chromosome, such as are used in Drosophila. Such methods are being developed in mice, but cure not yet suitable for routine use. 

Figure 13.2 E. coli tryptophan (trp) operon. o, operator L, leader a, attenuator E, D, C, B, A, structural genes. Numbers are base pairs.

Type 2 MTs, also currently understood to function exclusively as OMTs, are found in all lignin-producing plants. This family is specific for coenzyme A derivatized phenylpropanoid compounds and appears to be less diverse in sequence and gene number than the type 1 family of MTs (Fig. 2.3). Based on database searches, type 2 OMTs consist of caffeoyl and feruloyl coenzyme-A specific OMTs (CCoAOMTs). The most closely related enzymes to plant CCoAOMTs are the mammalian small molecule methyltransferases, including catechol OMT and bacterial MTs involved in macrolide biosynthesis. 

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