Chemical analysis of chromosomes show that they consist of four basic compounds.
So the boys, despite having an XY chromosome, appear female when they are born.
Children with the condition are genetically male, meaning they have one X and one Y chromosome.
When she was pregnant, it was discovered that her baby had Ring 18, a rare chromosome disorder.
It can help prevent chromosome breakage, which is known to cause birth defects and miscarriages.
I wanted to get finished fast so I picked the smallest one to map, which is chromosome 21, he said.
She is the only child in the UK with this condition where part of one of her chromosomes is missing.