This would happen if she received one gene mutation from her father and her mother was a carrier.
Green said she can remember testing one young woman who was colour blind. She knew her father was colour blind as well, she said, but her mother must have been a carrier. The woman’s sons were also colour blind.
“If she had two mutations, then all her sons would get the X with the mutation and be colour blind,” Green said.
Many people are never assessed for colour blindness. Green said they may realize they have difficulty with colours, but don’t have a reason to be tested.
“They know the colour that grass is, is green,” she said, “and even if they don’t see it exactly like somebody else, anything else that is that colour is also green, and so on.”
Some people who are red/green colour blind can also function well, she said. They may not be able to see the colours accurately on a traffic light, but they know the order of red, yellow and green.
In many professions, it doesn’t make a difference, Green said, unless a student plans to pursue a career as a pilot, police officer or in a navigational field.
There are different degrees of color blindness, she said, and the cases being picked up at the Marine Institute are likely in the intermediate level if it wasn’t obvious to the students previously.
Some have no trouble distinguishing between different colours; they just see them slightly different from other people, Green said. But in navigation fields, she said, “you absolutely have to distinguish between red and green” in order to know whether that ship coming toward you is on your left or right.
Over the years, Green said she’s been asked to do colour vision testing and, sometimes, a hereditary disease called cone dystrophy is the cause, where the cones in the retina that can see colour are not working. But in these cases, she said, these people will also have severe decreased vision.
Red/green colour blindness is much more common than most genetic conditions, Green said, but it’s not really a disability for most people. It can make a difference in your career choice, she said, but it’s not an illness.
In classes of about 60 medical students, Green said there’s often two or three male students who are red/green colour blind. She discovers it when she demonstrates how the testing is done using slides with various layers of colours and a number. Anyone with red/green colour blindness doesn’t see a number there, she said, while other students will see a five or seven in the middle of the coloured dots. Some have already known they’re colour blind, she said, while others have had no idea.
While there has been research to correct colour blindness in animals, Green said gene therapy is a long, complex process and researchers are not near the point of testing this out in people.