The phase of the cell cycle one would expect triploid cells to be unable to complete would be Meiosis I.
<h3>Meiosis I</h3>
During meiosis I, homologous chromosomes pair up to form bivalents or tetrads. This means that for a triploid cell, one chromosome will not have a partner to pair with.
The existence of an unpaired chromosome after the pairing of homologous chromosomes will make the remaining processes of meiosis I likely impossible.
