In a recent study, scientists at the Milner Centre for Evolution at the University of Bath claimed that “selfish chromosomes” are to blame for the majority of human embryos dying prematurely. Over half of fertilized eggs die extremely early, often before a woman even realizes she is pregnant. The study, which was released in the journal PLoS Biology, explains why human embryos fail to survive while fish embryos typically have little effect on the treatment of infertility. Additionally, ANI said that if by chance any survivors are aborted after a few weeks.
Despite thousands of years of evolution, Professor Laurence Hurst, Director of the Milner Centre for Evolution, investigated why it’s challenging for humans to conceive. Numerous deaths are directly caused by the erroneous chromosome count in the embryos. There should be 46 chromosomes total in the fertilized eggs, 23 from each parent.
According to Professor Hurst, practically all embryos with the incorrect number of chromosomes—often 45 or 47—die in the womb. About 80% of unfortunate cases, including Down syndrome with three copies of chromosome 21, will not survive to term.
“This first phase of creating eggs is peculiar, the professor explains. An egg will receive one of a pair of chromosomes, while the other is destroyed. However, if a chromosome “knows” it will be destroyed, it essentially has nothing to lose. Remarkable recent molecular research has revealed that certain chromosomes change their behavior to avoid being destroyed when they sense that they are about to be destroyed at this initial step. This behavior could result in chromosome loss or gain as well as the death of the baby.” If the loss of an embryo would be advantageous to the mother’s other children, the selfish chromosomes are usually found in siblings and will receive extra nutrition.
The researcher went on to say that fish and amphibians do not have this issue. “In over 2000 fish embryos, no one with chromosomal defects from mom was detected,” he claimed. Birds also have a relatively low rate—roughly 1/25th of what all mammals experience—and Hurst suggested that this is likely due to nestling competition, which only happens after the birds have hatched.
Humans can only have one child at a time, therefore when an early embryo dies, the mother can start another pregnancy right afterward without realizing that her egg has been fertilized.