In some cases, the extra chromosome is very small and has no effect on a person's health.

He'd still look like a standard male, but he'd have this extra chromosome.

Time magazine reported in 1957 that Gibson was forced to take a test to see if she had an extra chromosome.

Down's syndrome, he said, was caused by an extra chromosome, but no one knew exactly how it occurred.

Having extra or abnormal chromosomes changes the way the brain and body develop.

"He doesn't have the extra chromosome," as a friend of his puts it.

Mosaic - only some of the cells have an extra chromosome 21.

The extra chromosome has been systematically added to every cell in her body.

This results in an extra chromosome, making the haploid number 24 rather than 23.

For example, Down syndrome is caused by having an extra chromosome in each cell.