Answer
Two copies of the same chromosome could appear in the same daughter cell if the microtubule connection breaks before the sister chromatids are separated. Another scenario of the same result would be if the microtubules of the same spindle pole attached to the kinetochores of the chromosome.
Work Step by Step
In the event that the microtubules of the same spindle pole attached to both kinetochores of the chromosome, the resulting daughter cell would have 3 parts of either the maternal or paternal homolog, while the other daughter cell would have only one. This would be the case with mitosis, which is the type of cell division specific to somatic cells. In the case of cells formed through meiosis, germ/sex cells, this same scenario would cause the chromosomal mistake to be propagated in every cell of the offspring. This is the case with Down's Syndrome, in which the offspring is born with an extra 21st chromosome.
