Since colorblindness can be due to different gene mutations, located on different chromosomes, the correct answer would be choice 1--chromosomal abnormalities. Color-blindness is inherited on the X chromosome as a sex-linked recessive condition. It is passed usually from mother's to sons. If the female has an X with the normal gene and her other X is a carrier for the colorblind gene, half of her son's will inherit the normal X and have normal color vision, and the other half will inherit the X with the colorblind gene and be color blind. That is because males have only 1 X chromosome and their Y chromosome has no effect on color vision. Females have 2 X chromosomes. If one is normal and the other has the colorblind gene, they will only be carriers and not have colorblindness. However, chromosomes 2, 7, and 8 also have genes that affect color vision. Since there are several different gene mutations involved, on different chromosomes, depending on whether the colorblindness is yellow-blue, red-green, or the absence of color vision, the answer is chromosome abnormalities.