Chapter 5 – Sexual Differentiation and Behaviour

Read Coad, Anatomy & Physiology for Midwives, 4th edition, chapter 5.
Write out your answers to Coad, Chapter Case Study, page 116.
Create a Coad “Chapter 5 Study Sheet.” Include the following:

Learning Goals

□ Explain why sexual reproduction increases genetic diversity.

□ Describe how genetic sex is determined.

□ Explain embryologic sexual differentiation.

□ Describe normal gonadal development.

□ Explain the major roles of sex hormones.

□ Describe common disorders of sexual differentiation.

□ Recognize factors that influence sexual behavior from a biological perspective.

Essential Vocabulary

Genetics

Chromosome
Homologous chromosomes
Diploid
Haploid
Meiosis
Fertilization
Zygote

Sexual Development

Sexual dimorphism
Gonad
Gonadal ridge
Testis
Ovary
SRY gene
Müllerian ducts
Wolffian ducts
Testosterone
Dihydrotestosterone (DHT)
Anti-Müllerian Hormone (AMH)

Disorders

Disorders (Differences) of Sexual Development (DSD)
Ambiguous genitalia
Androgen insensitivity
Congenital adrenal hyperplasia (CAH)

Draw

Sex Determination Flowchart

XX
↓

Ovary develops

↓

Estrogen predominates

↓

Female internal and external genitalia

XY

↓

SRY gene present

↓

Testis develops

↓

Testosterone + AMH

↓

Male reproductive tract develops

Embryologic Development

Draw the embryo showing:

indifferent gonad
Müllerian ducts
Wolffian ducts

Then show what happens in:

female development
male development

Structures & Concepts I Must Know

Structure	Function
SRY gene	Initiates testicular development
Müllerian ducts	Develop into female reproductive organs if AMH is absent
Wolffian ducts	Develop into male reproductive organs under testosterone
Testes	Produce testosterone and AMH
Ovaries	Produce estrogen and progesterone

Processes I Must Understand

Genetic sex determination
Gonadal differentiation
Internal genital development
External genital development
Hormonal influence during fetal development
Pubertal sexual maturation (overview)

Midwifery Connections

Concept	Why a Midwife Cares
Normal sexual differentiation	Explains fetal development
Ambiguous genitalia	Initial newborn assessment and referral
Congenital adrenal hyperplasia	Potential neonatal emergency if salt-wasting is present
Sex determination	Counseling families regarding prenatal testing
Genetics	Explaining inheritance patterns to parents

Clinical Connections

Understand:

Why ultrasound cannot always determine fetal sex early.
Why cell-free fetal DNA testing may identify sex earlier than ultrasound.
Why ambiguous genitalia require careful evaluation before assigning a diagnosis.
Why CAH is a medical emergency in some newborns.
Why sex determination should be communicated carefully and only when reasonably certain.

Things Worth Memorizing

XX vs. XY chromosomes
Function of the SRY gene
Function of testosterone
Function of AMH
What Müllerian ducts become
What Wolffian ducts become
Basic timeline of sexual differentiation

Questions I Should Answer Without Looking

How is genetic sex determined?
What is the role of the SRY gene?
What are the Müllerian ducts?
What are the Wolffian ducts?
What hormone causes Müllerian duct regression?
What hormone supports Wolffian duct development?
When can fetal sex usually be determined by ultrasound?
Why can ambiguous genitalia occur?
What is congenital adrenal hyperplasia?
Why is CAH important for a midwife to recognize?

Compendium Entry

This chapter would probably become two pages in your Midwifery Compendium.

Page 1 — Sexual Differentiation

Include:

XX vs. XY pathway
SRY gene
Hormones involved
Müllerian vs. Wolffian derivatives
Timeline of fetal sexual development

Page 2 — Disorders of Sexual Differentiation

Summarize:

Ambiguous genitalia
Congenital adrenal hyperplasia
Androgen insensitivity syndrome
Initial assessment
Referral considerations

Quick Reference Cards

Potential cards from this chapter:

Sexual Differentiation Timeline
XX vs. XY Development
SRY Gene
Müllerian vs. Wolffian Ducts
Congenital Adrenal Hyperplasia (CAH)
Ambiguous Genitalia: Initial Assessment

A note on the “Behaviour” section

The title includes “Behaviour,” but if your primary goal is to become a competent CPM and eventually teach midwifery, I would give that portion less emphasis than the embryology and anatomy. Behavioral theories often reflect a mix of biology, psychology, sociology, and evolving research, whereas the embryologic development of the reproductive system is foundational science that you’ll use repeatedly in fetal development, genetics, ultrasound, and newborn assessment.

One study technique for this chapter

Create a single “Sexual Differentiation Timeline” that starts at fertilization and follows development through birth:

Fertilization → XX or XY chromosomes established.
Weeks 4–6 → Indifferent gonads and ducts present.
Week 6–7 → SRY gene (if present) initiates testis development.
Weeks 8–12 → Hormones direct internal and external genital differentiation.
Second trimester → External genitalia become increasingly distinguishable on ultrasound.
Birth → Newborn examination confirms external anatomy; any concerns such as ambiguous genitalia prompt further evaluation.

This timeline ties together genetics, embryology, endocrinology, and fetal development into one coherent sequence, making it much easier to remember than studying each topic in isolation.