Genetics & Foetal Development

[Caroline]

Hello Everyone,

This may not be the best place to post this, but search as I might, I cannot find the thread I was looking for. So, here it is...

Somewhere on this forum I read a post by an SO saying, if I remember correctly, that all babies start off as female. If I've recollected wrongly, please forgive me, but I'm geriatric, and my memory's going these days.

However, assuming that I did recollect correctly, here's what actually happens...

In human somatic (body) cells there are normally 46 chromosomes made up of 23 pairs. 44 of the 46 are called autosomes because they are not thought to determine gender. The other two are called sex chromosomes. Normal males have a relatively large X and a small Y sex chromosome and normal females have two X sex chromosomes.

When the germ, or generative cells, are formed in the body of the adult, these sex chromosomes become separated, so that a sperm carries either a single X or a single Y chromosome, whilst every egg carries a single X chromosome. At conception the new embryo will be XX or XY, according to whether the egg, which is always X, was fertilized by an X-bearing sperm or by a Y-bearing sperm. Thus the sperm controls the genetic sex of the child.

Although the sex of the embryo is determined at the time of conception, anatomical differences don't show until approximately two months later. In this 'indifferent stage' every foetus has the primitive structures necessary for either a male or a female system: there are both Wolffian ducts and Mullerian ducts.

Gonad is the term given to the undifferentiated organ that will later become either a testis an ovary. Testes develop earlier than ovaries. In an XY foetus, the gonads develop into testes. The testes then cause the Wolffian ducts to develop into the rest of the internal male system, and the Mullerian ducts to be suppressed. In an XX foetus, the gonads develop into ovaries, the Mullerian ducts then form the rest of the female internal system and the Wolffian ducts are suppressed.

It is important to understand not only that there is a single primitive structure in the indifferent stage from which the male or the female organs develop, but that, each reproductive organ in either sex has a counterpart in the opposite sex. For example, the penis of the male and the much smaller clitoris of the female both come from the embryonic genital tubercle or phallus. Men have a vestigial uterus, the utriculus masculinus in the prostate and women have a homologue prostate in the glands at the lower end of the urethra.

Every foetus, whether genetically male (XY) or female (XX), starts life with the capacity to develop either a male or female reproductive system. All foetuses have non-specific genitals for the first 8 weeks or so after conception. After a few weeks, in an XY foetus the non-specific genitals develop into male genitals under the influence of male hormones (androgens).

If the child is conceived with male (XY) sex chromosomes, embryonic testes develop inside the body and start to produce androgens. In some cases these androgens cannot complete the male genital development due to a rare inability to use the androgens that the testes produce so the development of the external genitals continues along female lines.

So in a genetically male (XY) foetus the active intervention of male hormones (androgens) is needed to produce a fully male system. A female body type with female external genitalia is the basic underlying human form.

I hope that clears it up for you.

Regards,

Caroline.

[Beauty]

btw. It was ok to put it here.

[Virginia]

Very informative Caroline! Sounds like you taught biology!
Love,
Deborah

[Caroline]

Very informative Caroline! Sounds like you taught biology!
Love,
Deborah

Hi Deborah,

No, I just practise it.

Kind regards,

Caroline.

[Caroline]

As a final note, people with one X and 2 Y's (XYY; Jacob syndrome) also experience some problems -- but -- despite some media coverage, they are not more prone to violence against people. An extra Y chromosome does not make one "hyper masculine"; male violence has many roots but they do not stem directly from the Y chromosome or being male itself.

Julie

Hi Julie,

Re your last point, I'm no longer up to date on this stuff, but I remember a guy called Yablonsky in the early 60's who was raving-on about how he'd discovered the secret of violent men and the extra Y chromosome. The view was so popular over here that it almost became a joke with the 'punchline' that more than half the male population of Scotland must have been 'Y-ed up' (it sounds better in the vernacular, believe me).

Kind regards,

Caroline.

[Josey]

Caroline,

Thank you so very much for explaining that process. I have read many times how that works but your explanation was clearer than most.

I have been told by a couple of doctors that, while the basic process produces XY and XX, there are also variants (other than XYY) that cause varius stages of development. In effect, what they were saying is that it is not just black and white. Some people are more male than others. It depends on how far along the development cycle that person went. Some may show as male but actually only be developed to the 60 or 70% level which means that person still has 30 to 40% female. What is your opinion of this? Just curious. It always seemed possible but seems a little confusing to me.

[Virginia]

What a great biology lesson - thanks girls!!!
I hope some of our other sisters can appreciate the expertise that is available on this forum.
Again, well done, ladies!
Love,
Deborah

[Sally]

It can also often be useful to those people who are interested in the medical and scientific areas on this subject to look at the effect and timing testosterone has on the development of the maleness of a foetus.

Whilst we know that that the SRY gene causes the foetus to release TDF, (Testes Determing Factor) which turns the undifferentiated gonad into testes and once they are formed they release androgens such as testosterone, dehydrocorticosterone and anti mullerian hormone, which then continues the biological process, it is also known that sexual differentiation, physical,mental and emotional are also produced by hormones which may be amplified and/or specified by one's social environment during foetal life, the amount present or the absence of testosterone determines our maleness, mentally and emotionally.

There are key times or periods during the development when the foetus will go towards the male or the female, depending on the level of testosterone.
The window of opportunity may be only open for anywhere from 24 to 72 hours and if the required level of testosterone is not present, a basic female orientation to varying degrees develops, regardless of the testosterone levels before or after the critical periods.

The first critical period is at conception when the presence of the SRY gene (Sex determing region of the Y chromosome) will determine physical gender. There are many deviations which occur along the way as the primary sexual differentiation proceeds towards our physical gender. Some researchers call these 'experiments of nature', e.g. congential adrenal hyperplasia, when the female foetus releases a steroid hormone from her adrenal glands which resembles testosterone. The child which forms in this case is more often born with confusing genitalia.

It has also been argued by medical scientists that one's brain receptors for hormones may also play a significant role in our gender development. It's also believed that the mothers state of health, physically and emotionally during the critical times can have a significant effect on the gender development of the foetus, due to her health effecting the levels and timing of thre required testosterone showers.

I tend to agree with those medical people who see gender not as a bimodal male or female single difference, but more as a matrix, a male and female mix within the same person. I believe there are many independant attributes which can be linked together which make it possible for an individual to view themselves and function as male or female to varying degrees. The age old theory that each individual was either one of two, i.e non-overlapping male with female, has really been put to bed. Physical attributes can no longer be the sole determining factor with regards to gender. There definitely is a grey section and it may well be the case that if we put pure male at one end and pure female at the other end, the varying 'grey section' between the two may be the majority and not the minority as once believed.

Regards to all.

Sally.

[Lorna]

This is very informative, Caroline. Thanks for posting it!

I do recall hearing that every human life starts as female... it is the Y chromosome that determines our sex. Makes perfect sense!

Now I just wish I paid more attention in biology class...

[Caroline]

Caroline,

Thank you so very much for explaining that process. I have read many times how that works but your explanation was clearer than most.

I have been told by a couple of doctors that, while the basic process produces XY and XX, there are also variants (other than XYY) that cause varius stages of development. In effect, what they were saying is that it is not just black and white. Some people are more male than others. It depends on how far along the development cycle that person went. Some may show as male but actually only be developed to the 60 or 70% level which means that person still has 30 to 40% female. What is your opinion of this? Just curious. It always seemed possible but seems a little confusing to me.

Hi Josey,

Thanks for your kind words.

Regarding your final question, there are others responding to this topic who have more up-to-date and knowledgeable information on the subject than me, so will leave it to them, if you don't mind. Suffice to say that I agree with Sally,

I tend to agree with those medical people who see gender not as a bimodal male or female single difference, but more as a matrix, a male and female mix within the same person. I believe there are many independant attributes which can be linked together which make it possible for an individual to view themselves and function as male or female to varying degrees. The age old theory that each individual was either one of two, i.e non-overlapping male with female, has really been put to bed. Physical attributes can no longer be the sole determining factor with regards to gender. There definitely is a grey section and it may well be the case that if we put pure male at one end and pure female at the other end, the varying 'grey section' between the two may be the majority and not the minority as once believed. [unquote]

Kind regards,

Caroline.

[Virginia]

Ok where is Beauty???? dehydrocorticosterone - dehydrocorticosterone?
PLEASE???!!! There are still a few of us blondes that post here, do you know how long it took me to even type that word?? I even have trouble with testostrone (no smart remarks!) I think that Beauty needs to look up the meaning of (here we go again) dehydrocorticosterone it may be a band word on this forum - just kidding girls!
I am however - impressed and I have a minor in biology and I ain't never seed sucha combinatin of letters that being (Oh, Gawd - why me?) dehydrocorticosterone.
I still love you girls, now I got another headache!
Deborah