h32;102

Dp(1;Y)mal⁺/T(1;4)mscd1 males are fertile. The fecundity of Dp(1;Ybb^-)Bar^S/T(1;4)mscd1 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)mscd1/Y males in the frequency of sex chromosome pairing.

T(1;4)mscd1 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)mscd1 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)mscd1 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)mscd1/0 males. T(1;4)mscd1/0 males have short bristles, abnormal abdomens and reduced viability. The major autosomes appear to be paired normally in meiocytes in T(1;4)mscd1/Y males. However, in 13.9% of meioses in mutant males, the X and Y chromosomes are not associated. The frequency of this phenotype is roughly the same at prophase and prometaphase/metaphase, suggesting a defect in pairing rather than cohesion. T(1;4)mscd1 causes meiotic drive; the ratio of Y-bearing progeny to X-bearing progeny of T(1;4)mscd1/Y males is reduced to 0.91. T(1;4)mscd1/Y males show a sperm differentiation defect apparent in late stages of maturation; as many as 10 spermatid nuclei per cyst fail to elongate properly, producing a round spermatid phenotype.

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