The data above represent the results of three different crosses involving the inheritance of a gene that determines whether a certain organism is blue or white. Which of the following best explains the mechanism of inheritance of the gene?

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To determine whether or not an allele is X-linked or autosomal, check for discrepancies between the male and female offspring. In cross 1 and 2, phenotypic ratios are different when comparing the male and female offspring.

If the allele for white is X-linked dominant, there must be some female offspring that are blue since both parents could have passed on an X chromosome with the allele for blue. This is not the case for cross 1.

The allele for blue being X-linked dominant is reasonable and matches the information in cross 2. The female parent can only pass the white allele. All male offsprings would therefore be white. The females will all be blue because they all inherit the father's allele for blue.