During his studies on genes in Drosophila that were sex-linked, T.H. Morgan found F₂ population phenotypic ratios deviated from the expected 9:3:3:1. Explain the conclusion he arrived at.
a) The genes in Drosophila are not sex-linked.
b) The genes in Drosophila do not follow Mendelian inheritance.
c) There was a mistake in T.H. Morgan's experiments.
d) The expected phenotypic ratio of 9:3:3:1 holds true.