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Human rDNA: evolutionary patterns within the genes and tandem arrays derived from multiple chromosomes
1A. I. DuPont Hospital for Children, Wilmington, Delaware 19899, USA. igonzale@nemours.org
Genomics
|May 15, 2001
Summary
Human ribosomal DNA (rDNA) arrays are highly homogenized across chromosomes via concerted evolution. This study reveals surprising homogeneity in non-rDNA sequences and divergent intergenic spacers within arrays.
Area of Science:
- Genetics
- Molecular Biology
- Human Genomics
Background:
- Human ribosomal DNA (rDNA) is organized in arrays on five chromosome pairs.
- Concerted evolution, through recombination and gene conversion, homogenizes these rDNA arrays.
- Previous studies lacked chromosome-specific rDNA sequence comparisons.
Purpose of the Study:
- To investigate rDNA homogenization efficiency along the rDNA.
- To compare homogenization within and between homologous and nonhomologous chromosomes.
- To analyze DNA sequence variation in human rDNA.
Main Methods:
- Cloning and sequencing of rDNA fragments from specific human acrocentric chromosomes.
- Measurement and comparison of DNA sequence variation.
- Analysis of regulatory, coding, and intergenic spacer regions.
Main Results:
- High homogeneity observed in rDNA regulatory and coding regions across all chromosomes.
- Unexpectedly high homogeneity found in adjacent distal non-rDNA sequences.
- Identification of one to three highly divergent intergenic spacer classes within each rDNA array.
Conclusions:
- Human rDNA arrays exhibit significant homogenization, even in flanking non-rDNA regions.
- Divergent intergenic spacers represent a distinct feature within rDNA arrays.
- This study provides insights into the mechanisms and extent of concerted evolution in humans.