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Another human chromosome is finished
  
By
Edward R. Winstead


Four down, twenty to go. A team of French and American scientists has filled in all the gaps on the draft sequence of human chromosome 14, bringing the number of completely sequenced human chromosomes to four.

With 87 million base pairs, chromosome 14 is the largest finished chromosome to date. A chromosome is considered finished when virtually all the sequencing errors and inconsistencies have been eliminated. Draft versions of the human genome were published in February 2002, and in the last three years, chromosomes 22, 21, and 20 have been completed.



Two genes that are critical to the body's immune response reside on chromosome 14. So do about 60 genes that, when defective, contribute to disorders such as spastic paraplegia and early-onset Alzheimer's.

The researchers, led by Jean Weissenbach and Roland Heilig of Genoscope, France's National Sequencing Center in Paris, identified 1,050 genes and gene fragments on the chromosome. They also found 393 'pseudogenes'—DNA sequences that look like genes but have probably lost the ability to function. The findings appear online in Nature.

By comparing the human genes to genes in other species, including the mouse and the freshwater pufferfish (Tetraodon nigroviridis), the researchers were able to propose biological functions for more than 96 percent of the genes.

Chromosome 14 contains human versions of two genes in sheep associated with unusually muscular hindquarters, a rare condition known as callipyge (from the Greek for beautiful buttocks). The genes—MEG3 and MEG8—are activated differently depending upon which parent they came from. This type of gene regulation is called genomic imprinting.

The largest gene on this chromosome, neurexin 3, may help researchers understand how human cells produce multiple proteins from the same gene sequence. This process is known as alternative splicing. Neurexin 3 contains at least five sites that may be essential for the production of distinct proteins, the researchers found.

See related GNN articles
»Comparing three species to identify mechanisms of imprinting
»The Legacy of Solid Gold
»A reference for the human genome: The Tetraodon pufferfish sequence

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Heilig, R. et al. The DNA sequence and analysis of human chromosome 14. Nature Published online January 1, 2002.
 

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