Y chromosome
The Y chromosome is one of two sex chromosomes in therian mammals and other organisms. Along with the X chromosome, it is part of the XY sex-determination system, in which the Y is the sex-determining because it is the presence or absence of Y chromosome that determines the male or female sex of offspring produced in sexual reproduction. In mammals, the Y chromosome contains the SRY gene, which triggers development of male gonads. The Y chromosome is passed only from male parents to male offspring.
Health
Mosaic Loss
Males can lose the Y chromosome in a subset of cells, known as mosaic loss. Mosaic loss is strongly associated with age, and smoking is another important risk factor for mosaic loss.
Mosaic loss may be related to health outcomes, indicating that the Y chromosome plays important roles outside of sex determination. Males with a higher percentage of hematopoietic stem cells lacking the Y chromosome have a higher risk of certain cancers and have a shorter life expectancy. In many cases, a cause and effect relationship between the Y chromosome and health outcomes has not been determined, and some propose loss of the Y chromosome could be a "neutral karyotype related to normal aging". However, a 2022 study showed that mosaic loss of the Y chromosome causally contributes to fibrosis, heart risks, and mortality.
Further studies are needed to understand how mosaic Y chromosome loss may contribute to other sex differences in health outcomes, such as how male smokers have between 1.5 and 2 times the risk of non-respiratory cancers as female smokers. Potential countermeasures identified so far include not smoking or stopping smoking and at least one potential drug that "may help counteract the harmful effects of the chromosome loss" is under investigation.
XX Male Syndrome
XX male syndrome occurs due to a genetic recombination in the formation of the male gametes, causing the SRY portion of the Y chromosome to move to the X chromosome.[8] When such an X chromosome is present in a zygote, male gonads develop because of the SRY gene.[8]
Brain Function
Research is currently investigating whether male-pattern neural development is a direct consequence of Y-chromosome-related gene expression or an indirect result of Y-chromosome-related androgenic hormone production.
Women
In 1974, male chromosomes were discovered in fetal cells in the blood circulation of women.
In 1996, it was found that male fetal progenitor cells could persist postpartum in the maternal blood stream for as long as 27 years.
A 2004 study at the Fred Hutchinson Cancer Research Center, Seattle, investigated the origin of male chromosomes found in the peripheral blood of women who had not had male progeny. A total of 120 subjects (women who had never had sons) were investigated, and it was found that 21% of them had male DNA. The subjects were categorised into four groups based on their case histories:
- Group A (8%) had had only female progeny
- Group B (22%) had a history of one or more miscarriages
- Group C (57%) had their pregnancies medically terminated
- Group D (10%) had never knowingly been pregnant before
The study suggests that possible reasons for occurrence of male chromosome microchimerism could be one or more of the following:
- Miscarriages
- Pregnancies
- Vanished male twins
- Sexual intercourse
A 2012 study at the same institute has detected cells with the Y chromosome in multiple areas of the brains of deceased women.
"It's a very nice piece of work, showing that gene loss in the male-specific region of the Y chromosome proceeds rapidly at first - exponentially in fact - but then reaches a point at which purifying selection brings this process to a halt."[1]
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