Scientists Discover Miscarriages Often Result from Chromosomal Abnormalities, Known as “Selfish Chromosomes” in Embryos.
The study conducted by researchers at the Milner Centre for Evolution at the University of Bath was published in the journal PLoS Biology.
Professor Laurence Hurst, director of the Milner Centre for Evolution, stated that a successfully fertilized egg typically contains a total of 46 chromosomes, comprising 23 from the mother’s egg and 23 from the father’s sperm. When the number of chromosomes is too few or too many (known as aneuploidy), the embryo develops abnormally, leading to miscarriage.
“Many embryos have an incorrect number of chromosomes, often 45 or 47. Almost all fetuses die while still in the womb,” he explained.
It is estimated that over 70% of human eggs are aneuploid. Scientists indicate that this abnormality arises during the early stages of egg production, known as meiosis I.
During this stage, half of the chromosomes are selected to be passed into the egg, while the other half are discarded. However, Hurst noted that some discarded chromosomes can become “selfish,” sneaking into the immature egg through a process called centromere dynamics, thereby creating aneuploidy.
“Recent molecular studies indicate that if chromosomes detect they are being discarded, they will intentionally alter themselves to prevent this process, leading to losses or increasing the chromosome count, resulting in embryo death,” Professor Hurst explained.
Aneuploidy can cause miscarriages in women. (Photo: Shutterstock)
By sabotaging the embryo, the “selfish” chromosomes ensure that the egg and other embryos have a higher chance of survival. Among the new embryos and eggs, there may be copies of those chromosomes, increasing the likelihood of their genetic material being passed on to the next generation.
“This reproductive compensation” occurs only in mammals, which carry developing young in the womb and continuously nourish them until birth. For instance, in species that give birth to multiple offspring, when aneuploidy kills some embryos, the remaining young receive more nutrients, thus increasing their chances of survival.
However, humans typically carry a single baby. After a miscarriage, the mother must wait a full 9 months before attempting fertilization again. This means the “selfish” chromosomes immediately have another chance to be passed into the embryo.
