You probably know by now that sex refers to the biological characteristics that make humans males or females. Gender, however, is a broader term that refers to how individuals express their identities. In this way, sex is directly influenced by genetics or chromosomes and brain chemistry or hormones. This explanation reviews the role of chromosomes and hormones in gender.
- First, the explanation will present the difference between chromosomes and hormones.
- Second, the explanation presents what hormonal differences exist between males and females.
- After, the explanation focuses on atypical sex chromosome patterns.
- Klinefelter's and Turner's Syndromes will be presented.
- Last, a short discussion on the role of chromosomes and hormones in gender development will be provided.
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.
Androgens cause the embryo to become a male, so the baby develops as a female without them.
Hormones are chemical substances that trigger different reactions in the body.
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.
For a human to show male characteristics first needs to have an XY chromosome pair, which will stimulate the presence of male genitals. Then the different hormone levels, e.g. high testosterone, will cause them to be more likely to be muscular and develop Adam's apple, among other 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.
Many psychological studies have researched the behavioural effects of testosterone, the most notable of which is aggression. For example, Van de Poll et al. (1988) demonstrated that female rats became more aggressive when injected with testosterone.
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.'
Research has shown that men and women actually produce the hormone in equal amounts during activities such as kissing and sex.
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.
Accompanying the male-like characteristics, these individuals were treated as males and no longer as females.
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.
This case study suggests that there is some biological basis to sex and gender because despite being raised socially as a girl, David still felt uncomfortable in this gender, probably due to the truth of his biological sex.
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.
The Role of Chromosomes And Hormones In Gender - Key takeaways
- Chromosomes and hormones influence the development of sex characteristics in males and females.
- There are differences between chromosomes and hormones. Chromosomes are inherited and can influence our physical appearance and are dictated by what we inherit from our parents. In comparison, hormones are chemicals that can dictate our behaviour and emotions.
- Males have XY chromosomes, while females have XX chromosomes.
- The difference between male and female hormones is the levels of specific hormones (testosterone, estrogen and oxytocin) in the body.
- Atypical sex chromosome patterns can lead to the development of Turner's syndrome and Klinefelter's syndrome.
References
- Visootsak, J., & Graham, J. M. (2006). Klinefelter syndrome and other sex chromosomal aneuploidies. Orphanet Journal of Rare Diseases, 1(1). https://doi.org/10.1186/1750-1172-1-42
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