Editor: Akhmetova Aigerim
Author: Bolysbek Dana
Meiosis is a type of cell division in which eggs and sperm are produced. It involves two stages of division that ultimately result in four cells with one copy of each paternal and maternal chromosome. Before division, genetic material from the paternal and maternal copies of each chromosome is exchanged through a process called meiotic recombination or crossing over.
Violation of recombination is the main cause of aneuploidy (the presence of an abnormal number of chromosomes). But the reasons were not completely clear, because until now there have been no attempts to directly measure the number of unchanged chromosomes in a large series of human oocytes - immature eggs.
A group of scientists conducted a large population analysis of non-exchangeable chromosomes in the fetal ovary. In total, they examined 7,396 oocytes from 160 tissue samples. To determine the total proportion of human oocytes containing one or more non-exchangeable chromosomes, they counted pairs of chromosomes that lacked the crossover-linked MLH1 protein.
The researchers found a surprisingly high rate of recombination failures: more than 7% of oocytes contain at least one pair of chromosomes without exchange.
The smallest autosomes (i.e. chromosomes 21 and 22) are most likely prone to recombination failures. There is also a subtle but statistically significant positive correlation between gestational age and the frequency of unchanged chromosomes. Observations indicate an increase in aneuploidy by 1.6 times in the older gestational age group.
After all, the new findings may have great practical clinical implications. “From our experience with counseling couples who have miscarried or have a baby with an extra or missing chromosome, it's clear that there is often accompanying guilt,” Hassold says. "Our results show that on the contrary, many of these chromosomal errors are simply built into human biology."
Source: https://medicalxpress.com/news/2020-12-human-egg-cells-imperfect-surpris...
