Answer: univalent

AnswerCrossword Clue
UNIVALENTUnpaired, as a chromosome
univalenthaving a valence of one; monovalent
univalenthaving a valency of one, capable of combining with one atom of hydrogen or its equivalent / a univalent radical
univalent(of a chromosome) single; unpaired; not possessing or joining its homologous chromosome in synapsis