Boy interrupted: Y-chromosome mutations reveal precariousness of male development

Biology News Net ^ | September 2, 2013 | NA

[neverdem]

The idea that men and women are fundamentally different from each other is widely accepted. And throughout the world, this has created distinct ideas about which social and physical characteristics are necessary in each gender to maintain healthy human development.

However, social revolutions throughout the last century have challenged traditional ideas about not only which traits are normal and necessary for survival, but also how humans acquire them. Thanks to a new study from researchers at Case Western Reserve University, science is continuing the charge.

By studying rare families in which a daughter shares the same Y chromosome as her father, Michael Weiss, MD, PhD, and his colleagues at the university's School of Medicine have determined that the pathway for male sexual development is not as consistent and robust as scientists have always assumed.

A team led by Weiss, chairman of the Department of Biochemistry, the Cowan-Blum Professor of Cancer Research, and a professor of biochemistry and medicine, has published a study in the Proceedings of the National Academy of Sciences that examines the function of the SRY gene. This gene is responsible for initiating the process that leads to male development.

"A general principle of developmental biology is that evolution favors reliability," Weiss explained. "Robust switches ensure that our genetic programs give rise to a consistent body plan to ensure that babies have one heart, two arms, ten fingers, and so forth."

Traditional viewpoints emphasize the uniformity of this process. The new research indicates that male sexual development is less stable than other genetic programs.

In fetal development, a gene located on the Y chromosome, called SRY, begins the process that leads to male development. All fetuses initially develop with female tissues, no matter what the sex will be at birth, so the master switch is responsible for initiating the transformation of female tissues into male tissues. From there, the testes develop and produce testosterone, which eventually forms the male's external genitalia.

The university's study employs mutated SRY genes shared by a father and a sterile XY daughter. Females usually develop with an XX pair, but, in these families, the father instead produced a daughter with an XY pair. This occurs during fetal development when the SRY gene's master switch fails to trigger. Internal female tissues, such as the uterus and fallopian tubes, continue to develop but are dysfunctional and infertile.

"Yet the father has the same Y chromosome and the same mutation as the daughter," Weiss pointed out. "And since he is a fertile male, we know that the switch must be poised right at its edge."

The team decided to measure the biochemical threshold of the SRY master switch.

"Our expectation was that we'd find that a factor of 100 or more—a severe insult to the Y-encoded switch—was necessary to alter development," Weiss said. "But what we found was that the SRY threshold, as probed in father-daughter pairs, is only a factor of two."

Therefore, human males actually develop near the edge of sexual ambiguity. This means that, unlike the robust genetic programs which develop other essential processes like heart function, the SRY gene master switch is particularly vulnerable to change. It only takes a slight deviation from the normal process to dramatically alter fetal sexual development.

Given the importance of sexual reproduction to the survival of a species, why do human SRY genes function so close to the boundary of infertility? The idea of an unreliable master switch might appear paradoxical, but a growing body of research suggests that it might be an evolutionary necessity.

Extensive studies of gender-associated styles of childhood play and the acquisition of social competencies by Dr. S. Baron-Cohen and colleagues at Cambridge University (UK) have highlighted the long-term effects of testosterone secretion by the fetal testis. Testosterone influences the patterning of the male brain during a critical window in human development.

And it is the SRY gene that sparks the genetic program leading to the formation of testes and the production of fetal testosterone.

"We have this tenuous switch on the Y chromosome, and we anticipate that its gift to humanity is variability in the pathway of male development from its earliest stages," Weiss said. "The essential idea is that our evolution has favored a broad range of social competencies. In prehistory, this range would have given a survival advantage to communities enriched by a diversity of gender styles."

In fact, certain aspects of modern history seem to parallel this idea.

Susan Case, PhD, a professor of organizational behavior at Case Western Reserve Weatherhead School of Management, who was not involved in the study, agreed with Weiss's argument and noted that "diverse mixes of people offer more varied perspectives, more ideas and solutions, and more challenges to long-accepted views." In the corporate world, for example, these differing styles increase creativity and problem solving, especially within a group.

The implications of Weiss's research suggest that elements of human culture, which had been assumed to be psychological or cultural, may be biological, instead. Therefore, human evolution would not have been dependent on consistency and homogeneity, but on their exact opposite.

Source : amanda.petrak@case.edu

[Doogle]

"really?"

[Billthedrill]

Yep, that's pretty much it. The lede, that Michael Weiss, MD, PhD, and his colleagues at the university's School of Medicine have determined that the pathway for male sexual development is not as consistent and robust as scientists have always assumed, is pretty deceptive. What the work actually demonstrates is that the process really is as consistent and robust as scientists have concluded, the evidence for which is that the XY female is as rare as it turns out to be.

This says nothing about "gender," which is a latter-day invention of social scientists, and it has nothing to do with homosexuality. This is straight embryology. Here, the scientific fact that a male has an X and a Y chromosome and a female, two X's except in exceedingly rare circumstances flies in the face of the "you are whatever you imagine yourself" vanity we get from the Studies faculties. Breath of fresh air, actually. The reporter may not agree but that's just too bad.

[Age of Reason]

Have you ever noticed that women have a sixth sense that they are being “checked out”. Being old and ugly but not dead, I am amazed how a woman will look around when a guy is admiring her attributes stealthily..

Maybe.

Or it could be that they are constantly looking around to see who's checking them out when you just happen to be doing so.

[Maelstorm]

Sure there are exceptions but the fact that they are rare means they are not to be confused with the overall rule. Male development is NOT precarious for the vast majority of individuals that is the fact since the beginning of humanity. Just as the vast majority of humanity are NOT born with downs syndrome or other forms of genetic anomaly.

[Bigg Red]

Have you ever noticed that women have a sixth sense that they are being “checked out”.

***
I do think that we women have a sense of when we are being watched. Probably some sort of protective mechanism to keep us from harm.

[cradle of freedom]

I think they also took a great deal of grant money from some devious evil people.

[cradle of freedom]

Homos would have been the first to die during the stone age.

[cradle of freedom]

Homos would have been the first to die during the stone age.

[I want the USA back]

This ‘study’ is about a very small number of people. However, it was applied to everyone.
This is poor science.

Also, it’s sex, not gender.

[workerbee]

It is impossible for a male cat to be “calico”

Unlikely, but not impossible.

[Rameumptom]

Nope. they are talking something simple most deer hunters know but gussying it up with too many fancy words. The more food and space there is the more bucks will be born. The less the food and the denser the population the more does will be born.

Men are more likely than women to have birth defects (like color blindness) because they are missing some genes on the missing part of the Y. Females have double insurance against color blindness. So it makes sense that the more stressful the environment for the mother the more likely things are to go wrong for the male.

then of course they had to add in the pc dribble

[NoCmpromiz]

It is impossible for a male cat to be “calico”

Ummm.. not really impossible.

They're just extremely rare and mostly sterile...

This from that bastion of all information that is mostly true, Wikipedia..

Calico cats are almost always female because the X chromosome determines the color of the cat and female cats, 
much like all female mammals, have two X chromosomes, whereas male mammals, including common male cats, have 
one X and one Y chromosome. Since the Y chromosome does not have any color genes, there is no chance he could 
have both orange and non-orange together. One main exception to this is when, in rare cases, a male has XXY 
chromosomes (see Klinefelter's syndrome), in which case the male could have tortoiseshell or calico markings. 
Male calico or tortoiseshell cats are sterile due to the abnormality of carrying two X chromosomes. Few of 
these males can breed (1 in 3,000) and are rejected by breeders for studding purposes and would, in any event, 
pass on only one of those X chromosomes to any male offspring, producing normal (non-calico) male kittens.

[Farnsworth]

HA!

[editor-surveyor]

The info that I got on this way back in the ‘70s was that an X chromosome can only provide two colors, and thus a female has no problem having abundant colors.

Yes, I have seen two male calicos, and I am 68 years old.

[Fire_on_High]

For a full, healthy male cat, yes. Genetic chimerism can account for it, or Kleinfelter’s (XXY).

Red and black are carried on the X chromosome, one or the other but not both. Calicos are normally female because XX means one chromosome carries the gene for red fur, one for black fur. The white patches are a different issue entirely and don’t have anything to do with this.

A genetic chimera has cells from two different animals in the same actual living beast, such as twins fused in utero. One can carry red, one black, and still be full male.

Kleinfelter’s is obvious...two X chromosomes, one can carry red and one black.

So not quite impossible...but a lot of stuff has to go wrong “just so”.

[1010RD]

And why polygyny is the norm in so many mammals.

[tekcomputers]

It’s not stupidity, but it’s not pseudo-science either.

If you want to see pseudo science you should look at any of the post that attempt to paint whether someone is born as male or female determined based on the presence of a Y chromosome..... THAT is pseudo-science. What is being seen is that it’s not nearly as simply as that, there are multiple genetic components that need to line up in order for a person to be born “male”. This article is dealing with a case of someone born with a condition known as Sawyer’s syndrome.... in this case the SRY gene trigger is nonfunctional... the SRY gene is what triggers male gonadal development. In such a case the person is born with gonads which may contain ovarian and testicular cells, and are non functional. As a result they do not release the necessary hormones for the development of secondary sexual characteristics and genital development and the person has a female phenotype at birth.

Another example of what can happen is with AIS(partial or complete), in that case the SRY gene is present and testicles develop, but due to an error on the AR gene which is located in the X chromosome the persons sells poorly react or (or in some cases do not react at all) to natural produced androgens from the gonads, and the genitals develop either completely female in appearance or ambiguous testicles do not descend and remain in the abdomen, and usually become even more feminine in appearance at puberty due to unused testosterone getting converted by the body to estrogen, feminizing the person in appearance even more. CAIS women especially will be even curvier withe larger breasts due the higher level of estrogen naturally in their system than what happens with non-CAIS females.

These conditions have existed for quite some time. Likely predating their “recent” diagnosis.... It was merely that we lacked the medical science at the time to fully comprehend what was happening and just made assumptions purely based upon phenotype. (aka, the baby is born with a vagina, so it’s a girl).

Don’t confuse our increase in understanding of what is going on and causes these types of conditions with “pseudo-science”.