RecQ5^D1/RecQ5^D2 mutant adult males do not show any obvious defects in the meiotic divisions and spermiogenesis, no gross morphological abnormalities are seen in spermatogonia, spermatocytes, spermatids or other cells in the mutant testes and active motile sperm are present. However, the apical region of the mutant testes is swelled compared to controls and the mutant testes display increased frequency of waste bags.

Embryos lacking maternally derived RecQ5 (i.e. from RecQ5^D1/RecQ5^D2 homozygous mothers), display asynchronous nuclei. Most comprised of pairs of nuclei, but sometimes more than three irregular nuclei are found to be clustered together. These pairs of abnormal nuclei are clonally generated from single parent nuclei. The parent nucleus and its daughter nuclei proceed synchronously with the surrounding nuclei in prophase, metaphase, anaphase, telophase and interphase.

Homozygous RecQ5^D2 mutants are viable and fertile with no apparent morphological abnormalities.

Embryos derived from RecQ5^D2 homozygous mothers display normal syncytial nuclei division. However, every mutant embryo has at least 1 abnormal nucleus at cycle 13. In addition, the irregular nuclei are round in shape, even at anaphase, whereas the other nuclei show condensed chromosomes. The irregular nuclei exit from the synchronous cycles of normal syncytial mitosis.

Embryos derived from females heterozygous for wild-type and RecQ5^D2 are similar to wild-type embryos.