Monday, 11 June 2018

Secrets of the Y Chromosome

In advance of Father’s Day, let’s take a flash to map out the differences and similarities between “Dad jeans” and “Dad genes.”

Dad jeans are articles of sex-specific leisure clothing, long mocked for being comfy, dumpy, and elastic-waisted but lately reinvented as a fashion trend, suitable for male bodies of all shapes and ages.

Dad genes are particles on the sex-specific Y chromosome, long mocked for being a stunted clump of the mostly useless nucleic waste but lately revealed as man’s fastest friend, essential to the health of male bodies and brains regardless of the age.

Yes, dear fathers et al. born with the appurtenances generally designated male.

We sleep in exciting times, which includes novel insights into the only chromosomal distinction between you and therefore the women now prowling the aisles at the ironmongery shop.

(“Didn’t he say he could use a replacement bow saw? Or some halogen light bulbs?”) Researchers have discovered that contrary to longstanding assumptions, the Y chromosome isn't limited to a couple of masculine tasks, like specifying human body parts during a developing embryo or replenishing the sperm supply in an adult man.

New evidence indicates that the Y chromosome participates in an array of essential, general-interest tasks in men, like stanching cancerous growth, keeping arteries clear and blocking the buildup of amyloid protein plaque within the brain.

As a large percentage of men age, their blood and other body cells begin to spontaneously jettison copies of the Y chromosome, sometimes quickly, sometimes slowly.

That unfortunate act of chromosomal decluttering appears to place the lads at a heightened risk of Alzheimer’s disease, leukemia, and other disorders.

“I’m quite certain,” said Lars Forsberg, a professor of medical genetics at Uppsala University in Sweden, “that the loss of the Y chromosome with age explains a really large proportion of the increased mortality in men, compared to women.”

Other researchers are tracing the evolution of the Y chromosome and comparing the version found in modern men with those of our close relatives, both living and extinct.

Takeaway A: we will drop the man-equals-caveman caricature.

Although human DNA has been found to contain vestiges of our dalliances with Neanderthals from about 50,000 years ago, none of these genomic imprints are on the human Y chromosome.

By the design of it, something specific to the Neanderthal Y chromosome ultimately proved inimical to human health and survival, then any trace of the Neanderthal Y chromosome was ejected from the human gene pool sort of a poorly matched kidney.

The system analogy could also be particularly apt.

Fernando Mendez, a geneticist, and his colleague Carlos Bustamante of Stanford University reported that during an ll|one amongst|one in every of"> one among the notable differences between the human and Neanderthal Y chromosomes lie in a gene linked to transplant rejection.

Whatever the reason for the purification of the human Y over time, women’s equivalent X chromosome doesn't appear to possess been similarly cleansed, with the result that ladies on the average could also be slightly more Neanderthal than men, which could explain our comparative fondness for animal print shoes.

Yes, but apercu B: Hang on to the gorilla suit.

From a worldwide genomic perspective, our closest living relative is that the chimpanzee, followed by the gorilla.

When it involves the Y chromosome, however, humans look considerably more Magilla than Bonzo.

Kateryna Makova, director of the middle for Medical Genomics at Penn State University and her colleagues recently determined that if you line up a man’s Y chromosome with a chimpanzee’s, only about 70 percent of the 2 spans will stay together.

Align a person's Y with a gorilla’s, and 83 percent of the paired chromosomes will comfortably conjoin.

Looking at nine distinct sets of genes that are identified on the human Y chromosome, Dr. Makova said, “eight of them are shared with the gorilla, while only six gene families are shared with the chimpanzee. It’s very surprising.”

The researchers propose that the observed patterns might be the result of mating practices.

Among gorillas, fertile females generally mate with one male at a time — the local silverback.

Women, too, are mostly, though by no means unerringly, monogamous.

By contrast, female chimpanzees mate wildly and promiscuously during each ovulatory cycle.

As a rule, female promiscuity promotes sperm competition among males, and since the Y chromosome oversees sperm production, Dr. Makova said, the chimpanzee Y is probably going to evolve at hyperspeed to stay up.

David Page of the Whitehead Institute in Cambridge, Mass., a world authority on the male chromosome who could rather be called the Y Guy, believes the Y and therefore the X “each deserve a full novel of their own.”

Whether within the double-X format that specifies a female fetus, or the X and Y pair found in males, the sex chromosomes stand aside from the opposite 22 normal chromosome pairs, or autosomes, that constitute the entire human genome which is stuffed into nearly every nucleus of the body.

That tendency toward molecular aloofness led to the initial designation of the feminine chromosome as “X,” for strange or unknown; the Y was simply named for a subsequent letter within the alphabet.

The Y chromosome may be a true chromosomal outlier, holding a fraction of the number of genes found on all the opposite chromosomes, including the X.

Its genetic impoverishment may be a legacy of its role in sex determination.

Among our pre-mammalian forebears, an offspring’s sex was dictated because it is today in crocodiles and turtles: not by genetics, but by temperature.

Among turtles, if an egg develops in warm conditions, the embryo turns female. If it’s
cooler outside, the embryo becomes male.

But with the increase of internal gestation and its uniform weather, embryos needed another clue for sex development.

That demand led to the evolution of male sex determination the gene called sry, and therefore the related got to keep the male and feminine genetic programs segregated.

As a result, the Y chromosome on which sry was located could not freely recombine and swap its pieces with its corresponding X chromosome, because the other chromosomal pairs do to freshen things up whenever a replacement egg or sperm is made.

Lacking the quality repair system of chromosomal recombination, genes on the Y chromosome began to decay and were eventually tossed out or reassigned to other chromosomes.

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