Publication Date:
2004-10-30
Description:
Because of its simplicity, the binary-switch nature of left-right asymmetry permits meaningful comparisons among many different organisms. Phylogenetic analyses of asymmetry variation, inheritance, and molecular mechanisms reveal unexpected insights into how development evolves. First, directional asymmetry, an evolutionary novelty, arose from nonheritable origins almost as often as from mutations, implying that genetic assimilation ("phenotype precedes genotype") is a common mode of evolution. Second, the molecular pathway directing hearts leftward-the nodal cascade-varies considerably among vertebrates (homology of form does not require homology of development) and was possibly co-opted from a preexisting asymmetrical chordate organ system. Finally, declining frequencies of spontaneous asymmetry reversal throughout vertebrate evolution suggest that heart development has become more canalized.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Palmer, A Richard -- New York, N.Y. -- Science. 2004 Oct 29;306(5697):828-33.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Systematics and Evolution Group, Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada. rich.palmer@ualberta.ca〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15514148" target="_blank"〉PubMed〈/a〉
Keywords:
Animals
;
*Biological Evolution
;
*Body Patterning
;
Brain/embryology/growth & development
;
Functional Laterality
;
Gene Expression Profiling
;
*Gene Expression Regulation, Developmental
;
Genotype
;
Heart/embryology/growth & development
;
Inheritance Patterns
;
Morphogenesis
;
Mutation
;
Phenotype
Print ISSN:
0036-8075
Electronic ISSN:
1095-9203
Topics:
Biology
,
Chemistry and Pharmacology
,
Computer Science
,
Medicine
,
Natural Sciences in General
,
Physics
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