Homozygous males are fertile, but their progeny show paternal chromosome loss (loss rate of paternal chromosome 4 is 14%). The timing of the chromosome loss is meiotic.

Wild-type frequencies of sex and 4th chromosome nondisjunction are seen in homozygous females. Homozygous males show no increase in sex chromosome nondisjunction or loss compared to wild type. They show increased 4th chromosome nondisjunction compared to wild type. Nondisjunction of chromosomes 2 and 3 is also seen. The frequency of 4th chromosome nondisjunction or loss does not increase with age. The defect appears to be specific to meiosis I. The transmission of the Dp(1;f)1187 chromosome is unaffected in mutant males. Transmission of the C(4)RM chromosome is similar in mutant males and controls. In homozygous males, the homologues of either one or both of the autosomal bivalents are separate in 10% of S6 stage meiocytes (this phenotype is not seen in wild-type males). Unpaired autosomes are frequently seen in homozygous meiocytes, often at or near the spindle poles, whereas the sex bivalent is intact and often positioned medially between the poles. The precocious separation of the 4th chromosome bivalent appears exaggerated in mutant cells, as the 4th chromosomes often reach the spindle poles before the sex chromosomes have visibly separated. No defects in meiotic spindles are seen in mutant males. The chromosomes are dispersed along the pole-to-pole axis in stage M2 and M3. Autosomal bivalents with an unusual dumbbell-like shape or separated by a slight gap are seen, suggesting that they are not as tightly associated as in wild type. These bivalents are also often displaced from the metaphase plate. The sex chromosomes are closely apposed in a configuration not discernibly different from wild type.