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Chromosomes and Hormones influencing gender - Coggle Diagram
Chromosomes and Hormones influencing gender
Biological sex is determined by the sex chromosomes X and Y (23rd chromosome) with xx being for females and XY being for males
Sex chromosomes contain genetic material that controls development as a male or female. During this process, sex hormones such as testosterone, oestrogen and oxytocin
Testosterone
A steroid hormone that stimulates development of male secondary sexual traits
It is found mostly in males but females also produce it, with about 10% of the amount found in males
The influence of testosterone on sexual differentiation of a foetus begins early in pregnancy and involves internal and external genitalia, as well as the brain and behaviour
The gonads are sex glands, testes in males and ovaries in females and these are orignally identical in both XY and XX embryos
If the gonads do not become testes, they become ovaries which do not produce lots of hormones prenatally
The SRY gene (sex determining region y)
On the Y chromosome and controls whether gonads become ovaries or testes
Therefore XY foetuses have higher levels of testosterone than XX foetuses, especially between 8 and 24 weeks of gestation. Between then and birth gonadal hormone levels are low in both sexes
A surge of testicular hormones after birth makes tesosterone once again higher in boys than girls for the first 6 months
Testosterone and the brain
It is associated with masculinisation of the brain, such as the development of brain areas linked to spatial skills
It is also associated with male behaviours such as competitiveness and aggressiveness
There are differences in the hypothalamus of males and females, with the sexual dimorphic nucleus bigger in males. These differences occur through the action of sex hormones
Acts as a hypothalamus, without this the brain develops as a female
Young - gave male hormones to female mice and female hormones to male mice. The effect was an irreversible change in the usual gender related behaviours. This suggests that hormones have a key role in determining gender behaviour
Deady - measured testosterone levels and gave the BSRI to women between 25 and 30, asking additional questions about maternal personality, reproductive ambition and the importance of a career. High testosterone levels negatively correlated with low measures of maternal personality and reproductive ambition
Oestrogen
A group of steroid hormones eg oestradiol, oestrone and oestriol which promotes the development and maintenance of female characteristics and regulates menstruation
Primarily a female hormone but small amounts are found in males
Affects physical changes such as development of breasts but has behavioral effects such as PMS/PMT which is associated with high emotions, irritability and anti social behaviour such as lack of control
The diminishing of oestrogen is associated with the onset of menopause
Plays a role in feminising the brain, it promotes neural interconnections for a more 'distributed' female brain (equal use of both hemispheres)
Abrecht and Pepe -increasing oestrogen levels in pregnant baboons heightened cortisol production which assisted development of organs and tissues in foetuses and led to reduced miscarriage by regulating progesterone. Suggests that oestrogen is key in maintaining and promoting pregnancy
Alonso and Rosenfield - Oestrogen is needed for development of body tissues associated with puberty in males and females . Supports the idea that it is associated with transformation into being sexually active and able in both genders
Oxytocin
A polypeptide hormone that also acts as a neurotransmitter and is produced in the brain by males and females to control the reproductive system
Its action is greater in females as it combines with oestrogen to enhance each others effect
Facilitates childbirth by helping stimulate contractions and breastfeeding by stimulating the 'let down' reflex
Increases five times during sex (though it drops in males immediately after orgasm)
Affects female social behaviour such as mate selection, nesting behaviour, monogamy, pair bonding and nurturing offspring
White-traut - measured oxytocin levels in saliva at different times and found that they were highest immediately before breastfeeding, decreased at initiation of feeding and rose again 30 minutes after feedings, illustrates the hormones important role in promoting breastfeeding
Insel - gave oxytocin to female prairie voles ( species which is monogamous ) and this led to them forming long term mating partnerships but when it was given to montane voles ( a multiple partner species ) it had no effects. Suggests it has a role in promoting pair bonding in monogamous species
Evaluation
Much research is conducted on animals. Human brains and development are more subject to social and cultural influences and they are more complex
Research on animals was unethical, prevented important survival aspects eg delayed care of maternal young
Too simple to think that testosterone is male and oestrogen and oxytocin are female. Both genders have all 3
Reductionist to perceive single hormones as having an effect on sex and gender. There are interactions between sex chromosomes, the SRY gene and hormones
A difficulty of research is that its hard to do it in a non invasive way. White traut did this