Chromosomes & Hormones

Question 1

Male Sex Development

Answer 1

1. Every foetus appears the same until a few weeks after conception
2. Sex organ development complete at ~3 months after conception
3. SRY causes production of testes
4. Lutropin produced in both sexes - in adrenal glands
5. Testes contain Leydig cells - respond to Lutropin by producing testosterone
6. Testosterone further drives male development

Question 2

Chromosomes

Answer 2

• Male Y chromosome determines male sex - contains SRY gene which causes male physical development at foetal stage
• SRY creates Sex-Determining Region Y Protein - transcription factor that binds to DNA to control other genes (epigenetic change)

Question 3

Atypical Sex Chromosome Patterns: Klinefelter’s Syndrome

Answer 3

• 1/1000 males
• XXY configuration
• Child born with penis, develops male traits
• Usually infertile, lacks muscular defintion, slim jaw, less facial hair, breast tissue forms

Question 4

Atypical Sex Chromosome Patterns: Turner’s Syndrome

Answer 4

• 1/2000 females
• XO configuration - damaged or missing chromosome
• Born with vagina and womb, but underdeveloped ovaries
• No monthly period, small webbed neck, narrow hips, nevi

Question 5

Testosterone

Answer 5

• Produced before birth
• Brain development affected by higher levels - studies show XX females are ‘tomboyish’ and prefer masculine activities in this case
• Testosterone surges in puberty drive secondary male characteristics
• Responsible for impulsiveness & competitiveness

Question 6

Testosterone Insensitivity

Answer 6

• No formation of male genitalia
• Often born/raised as girls
• Some identified as XY, and raised as boys

Question 7

Oestrogen

Answer 7

• Present in all foetuses - default gender is female
• Shi et al (2015): Oestrogen level associated with smaller brain size
• Promotes secondary female sex characteristics in puberty
• Controls menstrual cycle through increasing blood flow to uterus
• Elevated during pregnancy
• Responsible for maternal instinct and mood swings

Question 8

Oxytocin

Answer 8

• Produced in pituitary in response to skin to skin contact (eg. breastfeeding)
• Promotes bonding behaviours
• Causes milk production
• Enables post-orgasm bliss/contentment
• Helps in wound-healing
• Dampens fight or flight response in women (not in men - testosterone)
• Taylor et al (2000): Tend & Befriend response