Which statement is true about the genetic mode of inheritance for red-green color blindness?

• A. It is autosomal dominant
• B. It is autosomal recessive
• C. It is X-linked recessive
• D. It is Y-linked

Answer: (C)

Red-green color blindness is predominantly caused by mutations in genes that are located on the X chromosome. This condition is inherited in an X-linked recessive manner, meaning that the defective gene responsible for color blindness is situated on the X chromosome and affects males more frequently than females. Males, who have only one X chromosome (XY), will express the trait if they inherit a single copy of the mutant allele. In contrast, females, who have two X chromosomes (XX), would require two copies of the mutant allele to exhibit the condition, as one normal allele can mask the effect of the defective one.

This inheritance pattern explains why red-green color blindness is much more common in males than in females, as males cannot be "carriers" in the same way females can. If a male inherits an affected X chromosome, he will express color blindness. In contrast, a female could be a carrier with one affected X chromosome and one normal X chromosome without expressing the condition herself, depending on the inheritance of a second X chromosome.

This clearly differentiates it from the autosomal dominants and recessives, as well as Y-linked inheritance, which would only affect males in a very different manner.