Faut croire qu'il existe un complot planétaire pour cacher cette découverte juliénesque fondamentale: la probabilité de la réalité est nulle. En cherchant rapidement sur PubMed, j'ai trouvé des Canadiens*, des Chinois**, des Allemands***, des Espagnols****, des Français*****, des américains******... et ce n'est qu'un faible échantillonnage de tous les chercheurs, dans différents domaines scientifiques, qui sont unanimes à considérer que l'"apparition" par duplication d'un gène, suivit d'une évolution vers une nouvelle fonction n'a certainement pas une probabilité nulle.
Qui croire? Celui qui pose un problème mathématique en refusant d'envisager son inadéquation avec la réalité ou ceux qui, tout comme les cinglés du forum, tiennent l'évolution pour une réalité?
Jean-François
* Cross et al (2003) Genes, development and evolution of the placenta. lacenta 24(2-3):123-30
"...These insights suggest that most of the genes that evolved to regulate placental development are either identical to ones used in other organ systems (e.g., FGF and epithelial branching morphogenesis), were co-opted to take on new functions (e.g., AP-2gamma, Dlx3, Hand1), or arose via gene duplication to take on a specialized placental function (e.g., Gcm1, Mash2)."
** Chiang et al (2001) Characterization of duplicated zebrafish cyp19 genes. J Exp Zool 290(7):709-14
"... The CYP19 gene encodes cytochrome P450 aromatase, which catalyzes the synthesis of estrogens. Two cyp19 genes, termed cyp19a and cyp19b, have been isolated from zebrafish. Sequence comparison shows that Cyp19a and Cyp19b belong to two separate Cyp19 subfamilies. The cyp19a gene is expressed in the ovary, whereas cyp19b is expressed in the brain. The cyp19a and cyp19b genes are located on zebrafish chromosomes LG 18 and 25, respectively. Our data indicate that these gene loci arose through an ancient chromosomal duplication event. The expression of duplicated genes in distinct tissues may have evolutionary significance."
*** Strunkelnberg et al (2003) Interspecies Comparison of a Gene Pair with Partially Redundant Function: The rst and kirre Genes in D. virilis and D. melanogaster. J Mol Evol56(2):187-97
The D. melanogaster rst and kirre genes encode two highly related immunoglobulin-like cell adhesion molecules that function redundantly during embryonic muscle development. The two genes appear to be derived from a common ancestor by gene duplication. Gene duplications have been proposed to be of major evolutionary significance since duplicated redundant sequences can accumulate mutations without detrimental effects for the organism and leave the duplicated genes free to assume novel functions. To address the issue of conservation of the duplicated sequences and their putative redundancy, as well as to identify putative functional divergence of the paralogs during drosophilid evolution, we performed an interspecies comparison of the rst and kirre genes from D. virilis and D. melanogaster. The D. virilis genome contains orthologues of both rst and kirre and hence the duplication took place before the split of the two lineages and has subsequently been conserved. However, whilst the Rst orthologues show a high degree of sequence similarity, this similarity is lower in Kirre orthologues. Especially the intracellular domains of D. virilis and D. melanogaster Kirre sequences are highly divergent: the D. virilis kirre gene lacks the 3'-most exon present in D. melanogaster, which contains motifs conserved between kirre and rst in D. melanogaster. Hence, while each of the two genes is highly conserved at the level of its exon-intron organization, the selection forces acting on the rst and kirre coding sequences are different. These findings are discussed in the light of general evolutionary mechanisms."
**** Locascio et al (2002) Modularity and reshuffling of Snail and Slug expression during vertebrate evolution. Proc Natl Acad Sci U S 99(26):16841-6
"Gene duplication has been a major mechanism for increasing genomic complexity and variation during evolution. The evolutionary history of duplicated genes has been poorly studied along the vertebrate lineage. Here, we attempt to study that history by analyzing the expression of two members of the Snail family, Snail and Slug, in representatives of the major vertebrate groups. We find a surprising degree of variability in a subset of the expression sites for both genes in different species. Although some of the changes can be explained by neofunctionalization or subfunctionalization, others imply reciprocal changes in the expression of the two genes and the reappearance of expression in sites lost earlier in evolution. Because these changes do not fit easily into current models, we need to invoke additional mechanisms acting on enhancer elements to distribute expression domains and functions of duplicated genes unequally during evolution."
***** Balavoine et al (2002) Hox clusters and bilaterian phylogeny. 24(3):366-73
"A large Hox cluster comprising at least seven genes has evolved by gene duplications in the ancestors of bilaterians. It probably emerged from a mini-cluster of three or four genes that was present before the divergence of cnidarians and bilaterians. The comparison of Hox structural data in bilaterian phyla shows that the genes of the anterior part of the cluster have been more conserved than those of the posterior part. Some specific signature sequences, present in the form of signature residues within the homeodomain or conserved peptides outside the homeodomain, constitute phylogenetic evidence for the monophyly of protostomes and their division into ecdysozoans and lophotrochozoans. These conserved motifs may provide decisive arguments for the phylogenetic position of some enigmatic phyla."
******* Hughes (2002) Adaptive evolution after gene duplication. Trends Genet 18(9):433-4
"One of the two ribonuclease genes in a leaf-eating monkey has adapted to a role in the digestion of bacterial RNA. Following duplication of the ancestral ribonuclease gene, adaptation occurred through a series of changes in the amino acid sequence of the protein it encodes. This example is a good illustration of how specialization of protein function after gene duplication can be as source of novel protein functions."
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