For women, the biological clock starts ticking by their mid-30s at the latest: Fertility decreases, the risk of miscarriages increases. One of the main reasons behind both are eggs with altered chromosome numbers. It has remained largely unclear, however, why eggs from older women more frequently possess too many or too few chromosomes. A German-English research team has now discovered that certain structures on the egg’s chromosomes age and fall apart, possibly promoting incorrect chromosome distribution.
A new life begins when an egg is fertilized by a sperm. This is when the genetic information of the father and the mother is combined: Sperm and egg each contribute one copy of the 23 chromosomes that carry the genetic information (DNA), so that the newly formed embryo inherits a full set. However, the egg’s precursor cell contains two copies of each chromosome and, therefore, must eliminate half of its 46 chromosomes before fertilization. This…