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Four evolutionary strata on the human X chromosome.
1Howard Hughes Medical Institute, Whitehead Institute, and Department of Biology, Massachusetts Institute of Technology, 9 Cambridge Center, Cambridge, MA 02142, USA.
Science (New York, N.Y.)
|November 5, 1999
Summary
Human sex chromosomes evolved from autosomes, with nineteen ancestral genes differentiating into X-Y pairs. Their ages correlate with X chromosome locations, suggesting at least four evolutionary strata formed by recombination suppression events.
Area of Science:
- Evolutionary genetics
- Genomics
- Human genetics
Background:
- Human sex chromosomes (X and Y) originated from autosomes.
- Nineteen ancestral autosomal genes have homologs on both X and Y chromosomes.
Purpose of the Study:
- To investigate the evolutionary history and structure of human sex chromosomes.
- To determine the relationship between the age of X-Y gene pairs and their chromosomal locations.
Main Methods:
- Analysis of nucleotide divergence to estimate the ages of X-Y gene pairs.
- Mapping the locations of X-chromosome members of these gene pairs.
- Correlation analysis between gene pair age and chromosomal position.
Main Results:
- A strong correlation exists between the age of X-Y gene pairs and the location of their X homologs.
- Evidence for at least four distinct evolutionary strata on the X chromosome, characterized by decreasing gene pair age from the distal long arm to the distal short arm.
- These strata likely resulted from sequential suppression of X-Y recombination events.
Conclusions:
- Human sex chromosome evolution occurred in a stepwise manner, marked by at least four major recombination suppression events.
- The first differentiation event between X and Y chromosomes occurred approximately 240 to 320 million years ago.
- Gene order on the X chromosome remained largely intact during these evolutionary strata formation events.
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