Answer:
From the given choices, the most appropriate answer would be B. Anaphrase 1.
Anaphase I is the stage of meiosis I in which homologous chromosomes are pulled towards opposite poles with the help of spindle fibers.
The chromosomal defect which can occur in this stage is "unequal distribution of chromosomes in two daughter cells".
It may occur when the spindle fiber fails to attach to a particular chromosome.
It leads to the production of daughter cell or gamete with extra or decreased number of chromosomes.
When these types of gametes fertilize with other gametes, it may result in aneuploidy in the resulting offspring.