Mis-segregating chromosomesSTEFANO SANTAGUIDA, ANGELIKA AMON, MITAneuploidy—the incorrect number of chromosomes in a cell—is extremely common in early embryos and is the primary reason for pregnancy loss. A report published today (April 9) in Science reveals that one cause of this aneuploidy—aberrant cell divisions in the embryo—is linked to a genetic mutation carried by the mother. Astonishingly, this mutation turns out to be very common and appears to have been under positive selection during human evolution.
“There’s this genetic variant that they’ve been able to identify with very nice evidence for positive selection, but that has a fitness consequence, a fecundity consequence . . . that decreases the viability of an embryo,” said evolutionary geneticist Ed Green of the University of California, Santa Cruz, who was not involved in the work. “It flies in the face of what we think of in terms of positive Darwinian selection and demands an explanation.”
Approximately 75 percent of human embryos exhibit some form of aneuploidy and most of those will result in a failed pregnancy. Indeed, fewer than 30 percent of all conceptions are thought to result in an actual pregnancy. The likelihood of aneuploidy in a woman’s eggs—so called meiotic-origin aneuploidy—increases with age, ...
