Pollen
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Does cohesion fatigue play a role in the ‘maternal age effect’? The frequency of aneuploid conceptions in humans increases strikingly with maternal age, approaching 35% for women in their 40s. Remarkably, if studies of mouse oocytes are applicable to humans, it appears that the actual cohesin molecules that bind chromatids together in the oocytes of women may be decades old. In mammals, S phase in oocytes occurs only during fetal life when all of a female’s oocytes are formed. These arrest in prophase of meiosis I, where they remain for decades in humans, until ovulation when meiosis resumes and the chromosome segregation events take place. Because the active cohesin complexes between sister chromatids are only formed in S phase, those cohesin molecules must then also persist from fetal life until ovulation. In other studies of mouse oocytes, loss or degeneration of cohesins and meiotic segregation errors increase with age. Thus, cohesion fatigue may exploit the age-associated defects in oocyte cohesin and contribute to the increased incidence of aneuploid conceptions in older women.