In females homozygous for Syx13^ff16, the second stage of the formation of the chromocenter (joining two groups of nonhomologous chromosomes X-4 and 2-4 into a united ring structure -X-2-3-4-) is disturbed.

22.22% of bristles are reduced to a variable degree in homozygotes. Homozygous males show abnormalities in meiosis. The separation of chromatids at anaphase and telophase is delayed during the gonial divisions, in some cases showing bridge-like structures. Unequal distribution of chromosomes to the poles is seen in anaphase I. Metaphase II cysts contain cells with an abnormal number of chromosomes, indicating non-disjunction in the first meiotic division. Cells with a double spindle are seen in cysts at metaphase-telophase II. Each spindle has a normal number of chromosomes in these cells. The two spindles each have their own centrosome pairs, but have a common mid-zone. 18/24 cysts have spermatids with more than one nucleus at the onion stage. No motile sperm are seen in homozygous males. Homozygous females have morphologically abnormal ovaries, 35.3% of which have only abnormal long germaria without egg chambers at later stages. The number of ovarioles per ovary is only about half that of wild type. The average number of nurse cells per egg chamber is 12-14 in homozygous females and the number of nurse cells within the egg chambers varies significantly. Heterozygous females also show some reduction in the number of nurse cells per egg chamber compared to wild type. The karyosome is sometimes split into 2 or 3 parts in S7-12 stage homozygous egg chambers. The metaphase spindle is sometimes abnormal in stage S14 oocytes; a tripolar spindle and cleft spindles have been observed. In some cases, the early anaphase spindle appears to be separated into two halves along the equatorial zone and in addition, there appears to have been a cut of the spindle parallel to the spindle axis. Analysis of eggs taken from the uterus shows that homozygous oocytes enter into the second meiotic division and meiosis is completed irrespective of whether the eggs are fertilised or not. Chromosome pairing in homozygous stage S3-4 oocytes and nurse cells is abnormal; abnormal pairing of nonhomologous heterochromatin regions which form the chromocenter and also abnormal pairing of homologous euchromatic regions is seen. The metaphase index of homozygous larval neural ganglion cells (2.36 x 10^-2) is twice as high as in heterozygotes (0.8 x 10^-2) and homozygous cells show partial arrest of metaphase. A low frequency of chromosome fragments, chromosome non-disjunction, monopolar anaphases and abnormal spindles is seen in homozygous neuroblasts.