From Newsgroup: talk.origins
On 9/26/2025 12:15 AM, Pro Plyd wrote:
May be of interest to some
https://phys.org/news/2025-09-molecular-discovery-reveals-chromosomes- generation.html
When a woman becomes pregnant, the outcome of that
pregnancy depends on many thingsrCoincluding a crucial
event that happened while she was still growing
inside her own mother's womb. It depends on the
quality of the egg cells that were already forming
inside her fetal ovaries. The DNA-containing
chromosomes in those cells must be cut, spliced and
sorted perfectly. In males, the same process
produces sperm in the testes but occurs only after
puberty.
"If that goes wrong, then you end up with the wrong
number of chromosomes in the eggs or sperm," said
Neil Hunter, a professor in the Department of
Microbiology and Molecular Genetics at the
University of California, Davis. "This can result
in infertility, miscarriage or the birth of children
with genetic diseases."
In a paper published Sept. 24 in the journal Nature,
Hunter's team reports a major new discovery about a
process that helps safeguard against these mistakes.
He has pieced together the choreography of proteins
that connect matching chromosome pairsrCoensuring that
they are sorted correctly as egg and sperm cells
develop and divide.
...
When I started out as a genetic major in the mid 1970's it was already
being claimed that at least 1 recombination event per chromosome had to
occur to achieve successful meiosis. It was also known that tetrapod vertebrates like mammals and birds arrested meiosis I before chromosome segregation and cell division. Someone figured out that human females
had produced all the egg cells (arrested at meiosis I) by the age of
two. I don't know when this was determined. I only heard about it when
I was a TA for a human genetics class in graduate school in the 1980's.
This system likely evolved in vertebrates that sexually matured in a few
weeks or months to start the next generation like mice, but it doesn't
work so well in a species like humans that can have children half a
century after being born. It was believed that it is the main reason
that chromosome abnormalities like Down syndrome increase with the age
of the mother. The current trend of freezing eggs by young women is
probably a good idea. Eggs collected at a younger age are less likely
to be aneupoloid.
These researchers have identified proteins that protect and stabilize
the Holliday junction of recombining chromosomes in yeast. This is the
X structure that forms between chromsomes exchanging chromosomal
segments and was first proposed to exist by Holliday as part of the theoretical model of strand exchange between chromatids. Homologues of
these yeast proteins exist in mammals and birds so that is the reason
that the popular science article links their findings to stability in
Meiosis I.
https://www.nature.com/articles/s41586-025-09555-1
These proteins may be involved in the meiotic failures due to lack of recombination in Meiosis I. It is mostly identified in young women and
is not due to age, but is a mess up in the process of recombining the chromosomes.
Ron Okimoto
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