Cosmic radiation on the ISS is about 100 times greater than that on Earth, and increased radiation exposure is known to increase DNA damage in somatic and gamete cells. Once returned to Earth, the mouse sperm were compared with the control samples and assessed for damage; this included analysing their morphology, DNA, their ability to be used in fertilisation techniques, the in vitro development of subsequent embryos produced, and the normality of their offspring. More here.