Alleles undergo segregation is present in the mitosis. The answer is B. The first stage is prophase. The nucleolus disappears and the two centrosomes begin to form the mitotic spindle. The spindle xtends between two opposite poles f the cell. Next is the metaphase. The centromeres of the chromatid pairs align at the center of the miotic spindle. Then anaphase, the centromeres will split that separates the chromatid pair. In here, alleles are formed. They are now called chromosomes. The last phase is the telophase. The chromosomes will then form a thread-like chromatin and for ache envelope, a nucleoli appears.