1400 Genes Essential to Grow a Fish
A team from MIT scanned the genome of the zebrafish and concluded there are about 1400 genes essential for embryonic and early larval development. They did hands-on mutation experiments with 315 of these and found that mutations usually produced visible defects within 5 days that were invariably lethal. Estimating that they had experimented on about 25% of all essential genes, they say, “Our data suggest that there are roughly 1,400 embryonic-essential genes in the fish.” Comparing these genes with yeast, algae, mouse, human and worm genomes, they found many homologs that indicate these genes are all highly conserved, even though some of them build different structures. They feel, therefore, that the results help narrow down the class of essential genes required for embryological development of all organisms. Moreover, they feel these genes constitute an evolutionarily-conserved class in all living things, from yeast to humans:
The fact that there is such a small number of embryonic-essential genes and that they include genes that comprise coherent genetic pathways of development suggests that the genetically essential genes have a unique status in biological processes. Consistent with this possibility, we found that the yeast or worm orthologues of genes that are essential in fish have a high probability of also being essential in these species. Thus genes that can be detected in genetic screens, and in particular those that are essential for early viability, seem to have retained this special status through evolution. The implications of this observation are not known, but we suggest that these genes may be all or most of the genes that are absolutely required for many biological processes whereas most other genes may serve to assist these critical genes in making biological processes more robust. Evolution may have required that the number of genetically essential genes be small and that they remain the same genes.
1Amsterdam et al., “Identification of 315 genes essential for early zebrafish development,” Proceedings of the National Academy of Sciences USA, 10.1073/pnas.0403929101, online preprint July 15, 2004.
How on earth can these researchers consider 1400 essential genes a small number? How can they still believe evolution produced these genes, when mutations in any one of them cause death? A dead fish larva cannot evolve, because it cannot reproduce. 1400 genes! Think of it. Just getting one of them by chance is astronomically improbable, to say nothing of getting the second or third to match the first (see online book, p. 110). Forget it; it will never happen in this or any other universe.
By attributing the “special status” of these genes to Evolution, and by claiming that the personified tinkering goddess named Evolution “may have required that the number of genetically essential genes be small,” they are easy winners of Stupid Evolution Quote of the Week.