Blue-yellow color vision defects result from mutations in the OPN1SW gene. A single point mutation (meaning one single base pair difference) in a person with Tritanopia or Tritanomoly causes their blue-yellow color blindness. These mutations lead to the premature destruction of S cones or the production of defective S cones. Impaired S cone function alters perception of the color blue, making it difficult or impossible to detect differences between shades of blue and green and causing problems with distinguishing dark blue from black.
Tritanopia: People affected by tritanopia are dichromats. This means the S-cones are completely missing and only long- and medium-wavelength cones are present.
Tritanomaly: This is an alleviated form of blue-yellow color blindness, where the S-cones are present but do have some kind of mutation.
Emma and Kevin are brother and sister.
Kevin has tritanomaly, Emma can see color normally.
