Skin color is often one of the first traits people notice in each other. Studies in zebrafish uncovered a mutation that altered a transport protein and resulted in light-colored fish. This discovery led to the finding that the same gene in humans has a strong influence on skin pigmentation in many populations. The zebrafish mutation that reduced coloration created a null allele of the transport protein gene. Which of the following types of mutation would be most likely to create this null allele? a. a missense mutation b. a frameshift mutation c. a neutral mutation d. a silent mutation