HORMONES – SEX AND GENETICS

Genetic links
Genetic Link

 HORMONES AND SEX

For an exact determination of sex one has to distinguish between at least seven factors, and each of these factors can have atypical exceptions:

1. Chromosomal sex
2. Gonadal sex
3. Hormonal sex
4. Internal assessory internal structures
5. External sex organs
6. Sex of assignment or rearing
7. Sexual Self-identification

Chromosomal Sex

Typical:
The cells of a female body contain a.o. X chromosomes (XX).
The cells of a male X and one Y chromosome (XY).

Atypical:
In rare cases, there are problematic exceptions, for example combinations like XXY or XYY or XXX. Individuals born with these exceptional chromosome combinations have various problems of physical development or are infertile.

Gonadal Sex

Typical:
The female body has ovaries (female gonads or sex glands).
The male body has testicles (male gonads or sex glands).

Atypical:
In rare cases, ovarian and testicular tissue is found in the same body.

Hormonal Sex

Typical:
The gonads produce ‘female’ and ‘male’ hormones that play an important role in the development of the female or male body, especially before birth and during puberty, but also later in life.

Atypical: 
Note: Too much or too little of ‘male’ and ‘female’ sex hormones can have a decisive influence on the development and functioning of the body, and it can lead to an atypical physical appearance.

Internal accessory reproductive structures

Typical:
The female body has oviducts, a uterus, a
The male body has sperm ducts, seminal vesicles, a prostate etc.

Atypical:
In rare cases, these organs are underdeveloped or missing

External sex organs

Typical:
The female body has a clitoris, major (outer) lips and minor (inner) lips etc.
The male body has a penis and a scrotum.

Atypical:
In rare cases, these organs are underdeveloped or missing

Sex of assignment or rearing

Typical:
A child with a female body will usually be raised as a girl.
A child with a male body will usually be raised as a boy.

Atypical:
It is possible to raise a female child as a boy and a male child as a girl. Indeed, this happens in very rare cases

Sexual Self-identification

Typical:
A child with a female body raised as a girl will usually learn to consider herself female.
A child with a male body raised as a boy will usually consider himself male.

Atypical:
There are cases of children with female bodies raised as girls who nevertheless consider themselves male, and this can also happen vice versa, i.e. with male bodies raised as boys may nevertheless consider themselves female.

Hormones and Sexual Behavior


In everyday language people sometimes speak of “sex hormones”, which is misleading. may support the misconception that they determine sexual behavior: Moreso people think sex hormones mean an increase sexual desire; fewer sex hormones mean a decrease of sexual desire. At one time, it was also believed that the “sex hormones” determine a person’s sexual orientation. However, none of this has proven true. While hormones can be assumed to have some influence on behavior, is not quite clear what exactly this influence is

What are hormones?

Hormones (. : to stimulate) are chemical substances produced by internally secreting (. ) glands. These substances enter the bloodstream and stimulate various processes inside the body. In the context of human sexuality, the following three endocrine glands are especially important: 1. pituatary gland, 2. female or male gonads (ovaries or testicles) and 3. adrenal glands.

Genetic links
Sex Hormones

The production of “sex hormones” represents a feedback system

Two glands in the lower brain region (hypothalamus and pituitary gland) stimulate the gonads (ovaries in females; testicles in males) which, in turn, influence their stimulators. The different mixture of hormones in females and males, produces the secondary sexual characteristics as well as other differences between the sexes

Illustration 

 Hormones sexual determination
Hormone sexual determination

LH = Luteinizing Hormone; FSH = Follicle Stimulating Hormone. In females: LH plays an important role in the productions of estrogens and progesterone, FSH stimulates the development of egg cells (ova). In males: LH plays an important role in the production of testosterone; FSH plays an important role in the production of sperm.

How do the hormones determine a person’s sexual development?

In everyday language, people often distinguish between ‘female’ and ‘male’ hormones. However, this is misleading since both kinds of hormones are present in the bodies of both sexes. Typical of one or the other sex is the balance of these varies in different phases of a person’s life

B e f o r e  b i r t h

1. Primary sexual characteristics: Between the 12th and 17th week of pregnancy the fetus develops into a female or male, and this means, first of all, the formation of female or male sex organs. During this period, the level of testosterone is ten times higher in the male than in the female fetus. After that, the level is reduced and remains equal to that of the female until the onset of puberty, when it rises again.

2. Brain: Prenatal hormonal influences also produce a different development of the female or male brain. This is evident, for example, in the female pituitary gland which, in contrast to its male counterpart, remains capable of reacting in monthly cycles (menstruation). Because of these and other differences, one has even introduced the concept of “cerebral sex” as an additional factor in the determination of sex. However, it is still unclear if and how far these brain differences really determine the biological or psychosocial aspects of sex and behavior. Much more research is needed.

During Puberty 

During puberty the level of testosterone is slightly higher in boys than in girls. At the same time, the level of estrogen is much higher in girls than in boys. These differences in the hormonal balance contribute to the development of the secondary sexual characteristics.

Hormones and Sexual Behavior
everyday language people sometimes speak of “sex hormones”, but this is also misleading. It may support the misconception that they determine sexual behavior: More sex hormones mean an increase sexual desire; fewer sex hormones mean a decrease of sexual desire. At one time, it was also believed that the “sex hormones” determine a person’s sexual orientation. However, none of this has proven true. While hormones can be assumed to have some influence on behavior, is not quite clear what exactly this influence is.

Testosterone: Too little or too much?

Hormonal imbalances can lead to physical changes in adults, too. Examples: Growth of a beard in women, development of breasts in men. In either sex, a lack of testosterone can – but does not have to – lead to a lack of sexual desire. A very high level of testosterone may contribute to aggressiveness and increased sexual activity. However, it seems that psychosocial factors play a more important role in this regard 

Testosterone levels male
Testosterone levels male

Average curve of testosterone levels in males from childhood to late adulthood (years 0…60)/l of in plasma

What are the effects of castration on sexual behavior?

Castration, the surgical removal of the testicles, has different effects depending on whether it is performed before puberty or in adulthood. The following sections describe these effects in detail

What are the effects of castration on sexual behavior?

Castration in adulthood

In an adult, castration has a different effect: He also becomes infertile, but his sexual capacity, motivation, and performance do not necessarily come to an immediate end. In the long run, he will experience a considerable reduction in all of these areas, but the psychosocial may still be able to act out some of his earlier sexual scripts. A castration in adults can become necessary because of testicular cancer and other diseases. Usually beginning at age 50, a woman experiences her menopause, i.e. cessation of menstruation. This happens because the ovaries gradually cease their hormone production. This does not necessarily mean a weakening of her sexual response. Indeed, the response may even be strengthened for psychosocial reasons, for example, because she no longer has to fear pregnancy.

Estrogen levels female
Estrogen levels female

Average curve of estrogen levels in females from childhood to late adulthood (years 0…60)
Estrogens excreted in urine, mg per 24h

Reference http://www2.hu-berlin.de 

            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~            
                     

~ GENETICS OF SEX AND GENDER IDENTITY ~

By Tammy L. Romanuik

(August 2004)

Genetics and sex determination

Genetics is defined as the study of genes. Genes are composed of deoxyribonucleic acid (DNA) that can be passed down and inherited from one generation to the next. The information encoded in DNA is critical for determining the properties of a species1. DNA is divided into discrete molecules called chromosomes, each of which contains numerous genes.

results gametes
Results – gametes

Figure 1. Non-disjunction during meiosis II results in two normal gametes, one n+1 gamete, and one n-1 gamete. 

A ‘normal’ human cell is diploid (2n) because it contains 2 copies of each of the 23 chromosomes. Included in these 46 chromosomes are sex chromosomes X and Y. A normal human male has one X- and one Y- chromosome. They are often denoted 46, XY male. A normal human female has two X chromosomes, and is denoted 46, XX female.

In mitosis, for the cell to divide, it must replicate its DNA to create identical copies for its daughter cells. An example of mitosis is the development of multicellular organisms from a single-celled zygote (fertilized egg) [1]. Meiosis is essential for humans to produce sex cells (like sperm in men and eggs in women). It consists of two nuclear divisions resulting in haploid cells (n), which contain single copies of chromosomes. Haploid cells from a female and a male can fuse together to create a zygote with a unique combination of chromosomes. As indicated above, sex chromosome combinations include XX or XY.

Sex determination is genetically programmed by the X- and Y- chromosomes and is defined at the time of testes or ovary formation in embryonic development [2]. Testes formation in men is regulated by the expression of genes on the Y chromosome. Ovary formation occurs if the Y chromosome is not present and this DNA is not expressed. In addition to aiding in the development of primary sex characteristics mentioned above (sex organs involved in reproduction), the production of hormones like estrogen in women and testosterone in men is key for the development of secondary sex characteristics. Secondary sex characteristics develop later in life and often emphasize the assignment of female or male sex. Examples of secondary sex characteristics in the females include enlarged breasts, wide hips, less facial hair than men, and subcutaneous fat [3]. Examples of secondary sex characteristics in males include chest and facial hair, deep voices, and relatively larger body size [3]. These sex characteristics are important for humans to define their biological sex.

Results gametes
Results gametes

Figure 2. Non-disjunction during meiosis I results in two n+1 gametes and two n-1 gametes. 

Biological sex is identified based on the external genitalia (i.e. penis or vagina) and gonads (i.e. testes or ovaries) present in an individual. In contrast, gender identity refers to the self-identification in the brain of an individual as female or male. Most of the time sex and gender identity go hand in hand. However, unusual genetics may lead to biological sex ambiguities, discrepancies, and gender identity confusion [4].

Aneuploidy

Non-disjunction in meiosis I or meiosis II can lead to aneuploidy, an abnormal condition when an organism’s chromosome number differs from wild-type (normal). The result of non-disjunction in meiosis is two gametes (sex cells) with an extra chromosome (n + 1) and two gametes missing a chromosome (n – 1). The result of non-disjunction in meiosis II is one gamete with an extra chromosome (n + 1), one gamete missing a chromosome (n – 1), and two gametes with the correct number of chromosomes (n). A fusion of abnormal sex cells from males and females can create aneuploid zygotes 1. Several genetic disorders that are associated with aneuploidy and I will use Turner’s syndrome and Klinefelter syndrome as examples to show how aneuploidy affects sex and gender identity.

Results - Turner's Syndrome
Results – Turner’s Syndrome

Figure 3. Mosaicism occurs when tissues contain two genetically different cell lines. 

Turner’s syndrome: Affected individuals with Turner’s syndrome (TS) is genetically 45, X as they are completely or partially lacking a partner sex chromosome [1]. Cells that are completely lacking a partner sex chromosome have evolved from spontaneous non-disjunction during meiosis. Mosaicism occurs in females with TS when their tissues contain at least 2 different cell lines that differ genetically but are derived from a single zygote5. This is caused by a separate non-disjunction event occurring shortly after fertilization. 45,X/46, XX and 45X/46, XY are examples of mosaicisms, but there are other possibilities6. TS females have several distinguishing characteristics such as infertility (inability to have children), short stature, webbed skin behind the neck, low hairline, widely spaced nipples, small breast development, brown spots, small fingernails, and ovarian failure 1. The most obvious characteristics that lead to diagnosis are short stature and infertility.

Klinefelter’s syndrome: Affected individuals with Klinefelter syndrome are genetically 47, XXY [1]. The second X chromosome is often X-inactivated, meaning that it no longer functions to express its genes. Klinefelter syndrome develops when there is spontaneous non-disjunction in meiosis. Non-disjunction could occur either maternally (in the mother’s gamete) or paternally (in the father’s gamete) to create a 47, XXY zygote. Paternal non-disjunction in meiosis I account for 53% of cases, and maternal non-disjunction in meiosis I account for 34% of cases. The remainder of cases occurs in meiosis II. 15% of people with Klinefelter syndrome are 47, XXY/46, XY mosaics. Klinefelter’s syndrome is normally diagnosed during puberty [7]. Generally, men with Klinefelter’s syndrome can lead normal lives. They have several distinguishing characteristics such as sterility, tall stature, long arms and legs, lanky build, feminized physique, little chest hair, female patterned pubic hair, testicular atrophy, hypogonadism, osteoporosis, reduced aggression, language deficits, and breast development [1]. The low level of testosterone accounts for the lack of development of male secondary sex characteristics.

Conclusion

At the first glance sex identification appears simple. However, with closer examination, it is clear that aneuploidy is always a possibility and can make sex identification ambiguous and complex. Perhaps a further understanding of the biology of sexual differentiation will help our society realize that sex is not as clearcut as our ancestors would have us believe.

From: The Science Creative Quaterley – Jan – Mar 2007