ms(1)401/Y males do produce elongated spermatids, but the phenotype is characterised by the accumulation of late primary spermatocytes with regularly occurring extended cross invaginations of the nuclear membrane. The nucleoli are small, condensed and often fragmented and the Y tubuli appear more condensed than normal and appreciably reduced in numbers. The phenotype is fully expressed and easily detected in every cyst of mutant males. Abnormal nucleoli are recognisable early during spermatocyte growth, while the invagination of the nuclear membrane characterises the mature spermatocyte. ms(1)401/0 males show an earlier arrest in spermatid development than ms(1)401/Y males; Y tubular ribbons are completely missing and the primary spermatocyte cells do not reach the stage at which invaginations of the nuclear membrane occur. However, the phenotype is variable and in some cases very late individualised spermatids are seen.

ms(1)401¹ has male sterile phenotype, suppressible by Dp(1;Y)y²67g19.1

ms(1)401¹, ms(1)413¹ has lethal | male phenotype