Homozygous third larval instar ovaries have a normal overall morphology, and have the normal number and location of germline stem cells. 50% of ovarioles of newly eclosed homozygous females have 1-3 egg chambers (instead of 5 as in wild type) and no germline cells in the germarium. 13% have 1-3 egg chambers and undifferentiated germline cells in the germarium. 28% have 1-3 egg chambers and differentiated germline cells in the germarium. 4% have no egg chambers and undifferentiated germline cells in the germarium. 4% have no egg chambers and differentiated germline cells in the germarium. Germline clonal analysis indicates that fs(1)Yb is not required in the germline for fertility.

Follicle cells fail to invaginate between the developing egg cysts in the germarium, leading to a gap in the follicle cell layers between stage 1 egg chambers and the succeeding cyst. Composite chambers develop. Compound chambers in older females become increasingly disorganized, many containing dying germ cells with small pycnotic nuclei. Stalk cells appear to be missing, and egg chambers cluster together. Mutant eggs are smaller than wild type and have a dumpy phenotype because the dorsal surface is rounded. Dorsal appendages are often shortened and abnormally shaped. Mosaic analysis shows that fs(1)Yb is not required in the germline for proper oogenesis. Females carrying three doses of N⁺ (by virtue of N^+tCos479 or Dp(1;2)51b) are fertile, though with low fecundity. Homozygous fs(1)Yb^M104-1 females that are also heterozygous for loss of function N, da and Dl alleles show increased severity of ovarian mutant phenotype. Double heteozygotes for fs(1)Yb^M104-1 and a loss of function N allele are morphologically normal and fertile. Double heterozygotes of fs(1)Yb^M104-1 and mam² have weak but reproducible defects in ovary morphology, including absence of stalk cells and increased germ cell necrosis. No increase of severity of phenotype was observed for alleles of bib.

Ovaries have abnormally shaped yolks.

fails to lay eggs. ovaries with misshapen yolky eggs