h34;102

Dp(1;Y)mal⁺/T(1;4)mscd2 males are fertile. The fecundity of Dp(1;Ybb^-)Bar^S/T(1;4)mscd2 males is drastically reduced. Many males do not have motile sperm. Even in males that do have motile sperm, most mature sperm bundles have abnormal morphologies. A wide range of phenotypes is seen, from nearly normal bundles with 1-10 sperm nuclei of abnormal size or shape to entire cysts of abnormal sperm with round heads. Meiocytes of these males do not appear appreciably different from T(1;4)mscd2/Y males in the frequency of sex chromosome pairing.

T(1;4)mscd2 males show an increased frequency in X and 4th chromosome nondisjunction compared to wild type. X chromosome nondisjunction in females is not increased compared to wild type. The majority of aneuploidy caused by T(1;4)mscd2 can be attributed to meiosis I nondisjunction rather than meiosis II nondisjunction or chromosome loss. The major constriction within the X chromatin of the T(1;4)mscd2 chromosome is consistently reduced in size compared to wild type. Compensation (amplification of rDNA sequences on an X chromosome in an individual that lacks rDNA on the homologue) is not defective in T(1;4)mscd2/0 males. T(1;4)mscd2/0 males have short bristles, abnormal abdomens and reduced viability. The major autosomes and sex chromosomes appear to be paired normally in meiocytes in T(1;4)mscd2/Y males. Anaphase I figures are frequently abnormal. Chromatin bridges are seen in some cases. In some cases, sex chromosomes are seen near the metaphase I plate, while the autosomes are at the poles, and in some cases, the sex bivalents are seen near one pole. Bridges are not seen in meiosis II. T(1;4)mscd2 causes meiotic drive; the ratio of Y-bearing progeny to X-bearing progeny of T(1;4)mscd2/Y males is reduced to 0.73. Some spermatids have abnormal looking nuclei in T(1;4)mscd2/Y males.

The X^P4^D half of the translocation has not been recovered.