What causes red-green color blindness?

Red-green color blindness is primarily caused by a recessive gene located on the X chromosome. This means that for males, who have only one X chromosome, a single recessive allele is sufficient for them to express red-green color blindness. In contrast, females have two X chromosomes, so they would require two copies of the recessive allele to manifest the condition.

The genetic basis of red-green color blindness involves a mutation in the genes responsible for the photopigments in the cones of the retina that detect red and green wavelengths of light. Since this trait is linked to the X chromosome, it is more common in males than females, which is consistent with the patterns of inheritance observed in color blindness cases.

Other options do not accurately describe the genetic basis of red-green color blindness: a dominant gene, environmental factors, or referring to it as an autosomal dominant trait do not align with the established understanding of its inheritance pattern. Thus, the identification of the recessive gene on the X chromosome as the cause of red-green color blindness is well-supported by genetic studies and inheritance patterns.