The role of chromosomes and hormones

• 23rd pair of chromosomes is responsible for determining the biological sex of a baby
• Chromosomal structure

  Female - XX

  Male - XY
• Egg cells produced by ovaries have an X chromosome.

  Hold the sperm carry an X chromosome and the other half carry a Y chromosome.

  The baby sex is determined by the sperm that fertilises the egg.

  If fertilising sperm is X it will be a girl and if it is Y it will be a boy
• In males Y chromosome causes production of androgens (male hormones) - testosterone is the most important
• Testosterone leads to the development of the testes and penis
• Testosterone is released in higher quantities at puberty and causes secondary sexual characteristics such as facial hair and deepening voice.

  It is also associated with aggression
• In females, the absence of male hormones leads to development of ovaries and vagina.

  The ovaries then produce oestrogen.
• From puberty, oestrogen causes secondary sexual characteristics such as breast growth and menstrual cycle
• Oxytocin is sometimes known as the love hormone as it is produced by the pituitary gland.

  It stimulates lactation allowing mothers to breast feed. It reduces cortisol and facilitates bonding between males and females
• Females tend to have more oxytocin than males
• AO3 - David Reimer

  David Reiner was born a male but due to a bad surgery his penis was destroyed. He was brought up as a girl and called Brenda.

  He never adjusted to being a girl and this caused psychological problems, he changed back to a man and called himself David.Suggests chromomosomes are important
• AO3 - cogenital adrenal hyperplasia (CAH)

  CAH occurs when females have prenatallly high levels of male hormones resulting in external male genitalia. Whatever gender is assigned at birth is accepted by some, but not others.

  This suggests gender development is part biological and part experience.
• AO3 - Batista family from Dominican Republic

  Four children were born with external female genitalia and raised as girls. However at puberty the surge in testosterone caused their male genitalia to develop. They were genetically XY but due to faulty genes their male genitalia didn’t appear at birth.

  The girls accepted their male role without difficulty
• AO3 - Goozen

  Studied transgender individuals who were undergoing hormone treatment and being ingested with hormones of the opposite sex. Transgender women (male-female) showed decreases in aggression whilst transgender me were the opposite.

  Suggesting sex hormones do influence gender-related behaviours
• AO3 - Tricker

  Gave 43 males a weekly injection of testosterone or a placebo and found no significant differences in aggression after 10 weeks between the two groups.

  Suggests hormones dont fully influence behaviour like aggression and there are other factors.