The role of Chromosomes in Sex and Gender Flashcards
Biopsychologists assume that
gender identity and role arises from biological processes
i.e. gender differences are the result of sex differences, that is, women and men act, think and feel differently because of differences in how their brains work.
These brain differences may result from chromosomal and hormonal differences
Biological sex is determined by genes.
Each pair of chromosomes carry genes that control different characteristics
Humans have 23 pairs of chromosomes (in each cell of their body) - one pair (the sex chromosomes) determines an individual’s sex.
Males and females differ in their sex chromosomes:
Females have two X chromosomes (XX)
Males have an X and Y chromosome (XY)
There is usually a direct link between an individual’s chromosomal sex (XX and XY), their internal genitalia (ovaries or testes) and external genitalia (vagina or penis).
During prenatal development all individuals start out the same - a few weeks after conception both male and female embryos have external genitalia that look essentially feminine.
In male embryos, the SRY gene on the Y chromosome causes the gonad
(the organ which produces sex cells) to develop into testes (which then secrete testosterone), when the foetus is about 3 months old.
Testosterone stimulates the development of the male sex organs, but also causes the male brain to develop differently from the female brain.
A female’s gonad will develop into ovaries due to the absence of the SRY gene.
Testes/ovaries therefore strongly influence gender development, through the effects of the hormones they produce.
what did Reiner and Gearhart (2004) do
provide some insight into what can happen when genetically male children are sexually reassigned female and raised as girls.
They studied a sample of 14 children born with cloacal exstrophy (a severe birth defect where much of the abdominal organs - the bladder and intestines - are exposed, often causing the splitting of both male and female genitalia, specifically, the penis and clitoris respectively).
All were reassigned female at birth (born genetically male).
Reiner and Gearhart (2004)
Findings
Follow-up between the ages of 5 to 16 showed that 8 of the 14 who were reassigned identified themselves as boys (i.e. their gender identity matched their genetic sex).
All of the participants had at least moderately male-typical attitudes and interests.
This provides some support for the argument that biological variables have an impact on gender identity and behaviour, independent of socialisation (nurture),
The argument that gender identity is determined by genetic factors is also strengthened by the case of David Reimer.
David’s biological sex was male (XY), but despite being raised as a female and receiving female hormone treatment, he never fully came to identify himself as a female, and at the age of 13 reverted to his true sex- male- naming himself David.
Zhou et al. (1995) suggested that a
sex difference in the central subdivision bed nucleus of the stria terminalis (BSTc) may serve as a biological marker for gender identity, as the volume of BSTc is larger in males than in either females or male-to-female (MtF) transsexual women.
It has been argued that the size of this SDN (Sexually Dimorphic Nucleus) is determined by levels of testosterone in the womb. As David was exposed to normal levels of testosterone in the womb, his brain was arguably masculinised.
