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Molecular origins of rapid and continuous morphological evolution
John W Fondon1, Harold R Garner
1Eugene McDermott Center for Human Growth and Development and Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390-8591, USA. john.fondon@utsouthwestern.edu
Summary
Gene-associated tandem repeat expansions and contractions are a major source of evolutionary phenotypic variation. Repeat length variations in specific developmental genes correlate with significant morphological differences in dogs and other species.
Area of Science:
- Evolutionary biology
- Genomics
- Developmental biology
Background:
- Mutations in cis-regulatory sequences are considered the primary drivers of morphological evolution.
- The role of gene-associated tandem repeats in generating phenotypic variation remains underexplored.
Purpose of the Study:
- To investigate the hypothesis that tandem repeat expansions and contractions in developmental genes contribute significantly to phenotypic variation and evolution.
- To analyze repetitive elements within developmental genes across various dog breeds.
Main Methods:
- Comparative genomic analysis of repetitive elements in developmental genes from 92 dog breeds.
- Identification and quantification of repeat length polymorphisms.
- Association studies linking repeat variations to morphological traits.
Main Results:
- Evidence of selection for divergence at coding repeat loci, indicated by elevated purity and extensive length polymorphism.
- Quantitative association between repeat number variations in Alx-4 and Runx-2 genes and significant differences in limb and skull morphology.
- Similar repeat length variations observed in Runx-2, Twist, and Dlx-2 genes across multiple species.
Conclusions:
- Gene-associated tandem repeat variations are a significant source of phenotypic variation driving morphological evolution.
- Incremental effects and high frequency of repeat length mutations explain rapid, yet conservative, morphological evolution.