 Morgan et al.’s argument made use of a phenomenon that is called chromosomal non-disjunction. This term designates the failure of sister chromosomes to segregate during the process of meiosis. A possible result of this failure in Drosophila is a fly that has two female sex chromosomes in addition to a male one (XXY). The geneticists noticed that this would explain why some flies failed to exhibit an inheritance pattern normally exhibited by traits that are determined by sex-linked factors (i.e., factors that lie on one of the sex chromosomes X or Y), namely “criss-cross” inheritance. In this pattern, a recessive trait such as white eye color is transmitted from the females of the first generation to the males in the second generation, while the females revert to the original state of red eyes, hence the expression “criss-cross”. This normal pattern is explained by the fact that a recessive X-linked trait is always expressed in a male because there is only copy of the corresponding gene in a male. The female offspring, by contrast, receive a normal copy of the gene from their father, which is why the recessive trait will be hidden.