CHROMOSOMES AND HORMONES Flashcards
What are chromosomes?
Chromosomes are made of DNA and contain our genes they carry information in the form of genes. We have 23 pairs of chromosomes and the last pair pair determines biological sex.
What are the male and female chromosomes?
Females have XX sex chromosomes and males have XY.
Explain how the chromosomes are determined
Sex is determined by the sperm because normal egg cells always have an X chromosome. It is the sperm which can be either X or Y.
What does the Y chromosome carry?
Carries a SRY gene which causes the production of androgens: male sex hormones. These cause an embryo to develop as a male biologically - without androgens the embryo will develop female biological characteristics.
Explain the link between chromosomes and the genitalia of the child
There is usually a direct link between these chromosomes and the genitalia of the child due to the hormones that the developing foetus produces.
- All foetuses start as female and male genitalia start developing at around 8 weeks. This occurs because their chromosomes cause testes to be developed which produce testosterone (an androgen or male sex hormone) – this alters external genitalia and produces a baby of the male sex. Without androgens the embryo develops into a female.
How do hormones affect development?
- Prenatally (before birth) in the womb, hormones affect development of the brain and of the reproductive organs.
- At puberty, hormonal activity triggers secondary sexual characteristics such as pubic hair.
What are 3 important hormones that determine a person’s sex?
1) Testosterone
2) Oestrogen
3) Oxytocin
What is testosterone?
An androgen which controls the development of male sex organs and begins to be produced around 8 weeks of foetal development.
What does testosterone affect?
Affects brain development.
- XX females exposed to large amounts of androgens (testosterone) later show ‘tomboyish’ behaviour + greater interest in stereotypically male activities.
- Some research indicates that it also produces more physical and sexual aggression
- Testosterone production during puberty produces male secondary sexual characteristics of facial hair and deeper voice
What is oestrogen?
A female hormone that determines female sexual characteristics and menstruation.
What does oestrogen cause?
Causes some women to experience heigtened emotionality and irritability during their menstrual cycle. This is referred to as pre-mestrual syndrome (PMS).
What is oxytocin?
Promotes feelings of bonding in both sexes and is therefore known as the ‘love hormone’. Women typically produce oxytocin in larger amounts than men due to giving birth.
What does oxytocin do?
- stimulates lactation making it possible for mothers to breastfeed their children
- reduces cortisol and facilitates bonding - ‘love hormone’
- Produced in the pituitary gland causing feelings of contentment and calmness
When is oxytocin released?
Released in massive quantities during labour and after childbirth and makes mothers feel in love with their baby.
How is oxytocin related to fight or flight?
It reduces levels of cortisol (the main stress hormone) and therefore alters the ‘fight or flight’ stress response. In women oxytocin can produce a ‘tend and befriend’ response instead as it prompts women to look after their children and form protective alliances with others – this makes evolutionary sense as it keeps the family alive. However men are not affected in this way by oxytocin as testosterone counteracts it. Therefore men response to stress with the ‘fight or flight’ response.
