The Role of Chromosomes And Hormones In Gender

Difference Between Chromosomes and Hormones

Chromosomes are made of DNA, whilst genes are short DNA sections that determine living things' characteristics. Chromosomes come in pairs. There are 23 pairs in the human body (so 46 chromosomes overall). The last pair of chromosomes is what influences our biological sex. In females, the pair is XX, and for males, it is XY.

All eggs produced in the ovaries have an X chromosome. Some of the sperm have an X chromosome, while some other sperms have a Y chromosome. The sex of a baby is determined by the sperm that fertilises the egg cell.

If the sperm carries X chromosomes, the baby will be a girl. If it carries Y chromosomes, it will be a boy. This is because the Y chromosome carries a gene called the 'sex-determining region Y' or SRY. The SRY gene causes tests to develop in an XY embryo. These then produce androgens: male sex hormones.

Generally, females and males have the same hormones, but where these hormones concentrate and are produced will determine whether a human will develop male or female-like characteristics.

Difference between Male and Female Hormones

Chromosomes initially determine a person's sex, but most biological sex development comes from hormones. In the womb, hormones encourage the development of the brain and reproductive organs. Then, during adolescence, a burst of hormones induces the development of secondary sexual characteristics such as pubic hair and breast development.

Males and females have the same types of hormones but different levels of them.

Testosterone

Male developmental hormones are known as androgens, the most prominent of which is testosterone. Testosterone controls the development of male sex organs and begins to be produced at around eight weeks of fetal development.

Estrogen

Estrogen is the hormone that influences the development of female sex organs and menstruation.

Besides physical changes, the hormone can cause mood changes in women during menstruation, including increased irritability and emotionality. If these effects become severe enough to be considered diagnosable, they can be referred to as pre-menstrual tension (PMT) or pre-menstrual syndrome (PMS).

Oxytocin

Although both men and women produce oxytocin, women have it in much larger quantities than men. It plays a crucial role in female reproductive function, including childbirth.

Oxytocin stimulates lactation for breastfeeding. It also reduces the stress hormone cortisol and facilitates bonding, especially during labour and after childbirth. This hormone is often referred to as the 'love hormone.'

Atypical Sex Chromosome Patterns

Most humans present either an XX or XY sex chromosome pattern. This suggests that humans either show more female-like or male-like characteristics. Despite this, different patterns have been identified.

The sex-chromosome patterns that differ from the XX and XY formation, are called atypical sex chromosome patterns.

The most common atypical sex chromosome patterns are Klinefelter's syndrome and Turner's syndrome.

Klinefelter's Syndrome

In Klinefelter's syndrome, the sex chromosome present is XXY. In other words, this syndrome presents a male which the sex chromosome XY who presents an extra X chromosome. Although Klinefelter's syndrome is meant to affect 1 in 500 individuals, it is thought that around 2/3 of those with this syndrome are unaware of its presence ¹.

Characteristics of this syndrome include:

• Reduced body hair compared to XY males.
• Significant increase in height between the ages of 4 and 8.
• Development of breasts during puberty.
• Longer arms and legs.

Other common symptoms present in Klinefelter's syndrome are:

• Higher infertility rates.
• Poor language development.
• Poor memory skills.
• Passive and shy personality.

Turner's Syndrome

This syndrome occurs when a female only presents one X chromosome rather than a pair. Turner's syndrome is not as common as Klinefelter's syndrome since it affects 1 in 2,500 individuals.

The characteristics of this syndrome are as follows:

• Short height.
• Short neck.
• Lack of breasts and presence of a broad chest.
• Absence of menstrual cycle and infertility.
• Genu valgum. This refers to a misalignment between the centre of the leg articulations: hips, knees and ankles. Fig. 1. Representation of Genu Valgun and the missalignemt of the articulation centres.

Other common symptoms present in Turner's syndrome are:

• Poor spatial and visual abilities.
• Poor mathematical abilities.
• Social immaturity.
• High reading ability.

Discuss the Role of Chromosomes and Hormones in Gender Development

Some of the evidence brings to the fore the importance of the role that chromosomes and hormones have in the development of sexual characteristics regards hormone imbalances.

Congenital Adrenal Hyperplasia is a condition in which an individual shows the chromosome XY (male) but does not receive enough testosterone while in the womb. This makes the children to be born with female characteristics.

However, later in puberty, as hormonal changes occur, these individuals develop male-like characteristics.

Other research studies have suggested the critical interplay between chromosomes and hormones in gender development:

The Bruce Reimer Case Study

Brian and Bruce Reimer were twin boys born in Canada in 1965. Following a botched circumcision, Bruce was left without a penis.

Bruce's parents were directed to John Money, a psychologist pioneering his 'gender neutrality' theory, which suggests that gender is determined more by the environment rather than biological factors.

As a result, Money encouraged the Reimers to raise their son as a girl. 'Bruce', known as Brenda, played with dolls and wore girls' clothes. Although Money wrote extensively about the 'success' of this case, Bruce suffered from psychological problems, leading their parents to disclose the truth of their identity.

Following this, Bruce returned to life as a male, 'David'. Unfortunately, David suffered deeply due to their hidden identity and committed suicide in 2004.

Dabbs et al. (1995)

Dabbs and his colleagues studied testosterone levels in the prison population. They found that offenders with high testosterone levels were likelier to have committed violent or sexually motivated crimes. These suggest that hormones are linked to behaviour.

Van Goozen et al. (1995)

Van Goozen studied transgender individuals undergoing hormone therapy as part of their transition. This means they were injected with hormones of the opposite sex. Transgender women (men transitioning to women) showed a decrease in aggression and visuospatial skills, whilst the opposite was true for transgender men (women transitioning to men). This suggests that hormones influence the behaviour of men and women differently.