This chapter is a little different from the previous one. As a CPM, you are not expected to become a genetic counselor, but you do need to understand enough genetics to explain common inheritance patterns, discuss prenatal screening intelligently, recognize when referral is appropriate, and answer parents’ questions. I would focus on principles rather than memorizing rare disorders.

Chapter 7 – Overview of Human Genetics and Genetic Disorders

1. Read Coad, Anatomy & Physiology for Midwives, 4th edition, chapter 7.
2. Write out your answers to Coad, Chapter Case Study, page 161.
3. Create a Coad “Chapter 7 Study Sheet.” Include the following:

Learning Goals

□ Describe the structure and organization of DNA and chromosomes.

□ Explain how genes are expressed.

□ Distinguish dominant, recessive, and X-linked inheritance.

□ Interpret simple pedigree charts.

□ Explain the purpose and limitations of prenatal genetic screening.

□ Understand when referral for genetic counseling is appropriate.

□ Describe the role of genetics in modern midwifery.

Essential Vocabulary

DNA & Chromosomes

• DNA
• Gene
• Allele
• Chromosome
• Chromatin
• Genome
• Genotype
• Phenotype
• Mutation

Inheritance

• Autosomal dominant
• Autosomal recessive
• X-linked dominant
• X-linked recessive
• Carrier
• Homozygous
• Heterozygous
• Pedigree
• Penetrance
• Expressivity

Prenatal Testing

• NIPT (Non-Invasive Prenatal Testing)
• Cell-free fetal DNA (cfDNA)
• Carrier screening
• Chorionic Villus Sampling (CVS)
• Amniocentesis
• Genetic counseling

Draw From Memory

1. DNA Organization

Draw:

DNA

↓

Gene

↓

Chromosome

↓

Nucleus

↓

Cell

2. Simple Pedigree

Practice drawing symbols for:

• male
• female
• affected
• carrier
• pregnancy
• miscarriage
• twins

3. Inheritance Patterns

Sketch simple Punnett squares for:

• autosomal dominant
• autosomal recessive
• X-linked recessive

These are usually sufficient for midwifery-level genetics.

Concepts I Must Know

Processes I Must Understand

• Gene inheritance
• Cell division (review)
• Dominant inheritance
• Recessive inheritance
• X-linked inheritance
• Basic prenatal screening
• Difference between screening and diagnostic testing

Midwifery Connections

Clinical Connections

Be able to explain:

• Why NIPT is a screening test, not a diagnostic test.
• The difference between a positive screening result and a confirmed diagnosis.
• Why a normal ultrasound does not rule out every genetic condition.
• Why CVS and amniocentesis provide diagnostic information but carry procedural risks.
• Why obtaining a three-generation family history is valuable.

Things Worth Memorizing

• Humans have 46 chromosomes (23 pairs).
• One chromosome of each pair comes from each parent.
• Difference between genotype and phenotype.
• Difference between dominant and recessive inheritance.
• Difference between screening and diagnostic tests.
• Basic inheritance risk examples:
  • Autosomal dominant: affected parent → ~50% risk if heterozygous.
  • Autosomal recessive: two carriers → 25% affected, 50% carriers, 25% unaffected.
  • X-linked recessive: carrier mother → sons have a 50% chance of being affected.

Questions I Should Answer Without Looking

1. What is the difference between DNA, a gene, and a chromosome?
2. What is a mutation?
3. What is the difference between genotype and phenotype?
4. How does autosomal dominant inheritance work?
5. How does autosomal recessive inheritance work?
6. Why are X-linked disorders more common in males?
7. What information does a pedigree provide?
8. What is the purpose of NIPT?
9. What is the difference between a screening test and a diagnostic test?
10. When should a family be referred for genetic counseling?

Compendium Entry

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

Page 1 — Basic Genetics

Include:

• DNA → Gene → Chromosome diagram
• Chromosome pairs
• Key terminology

Page 2 — Inheritance Patterns

Summarize:

• Autosomal dominant
• Autosomal recessive
• X-linked recessive
• Common examples of each

Page 3 — Prenatal Genetic Screening

Include:

• NIPT
• Carrier screening
• CVS
• Amniocentesis
• Screening vs. diagnosis
• When to refer

Quick Reference Cards

This chapter naturally lends itself to cards on:

• Basic Genetics
• Autosomal Dominant Inheritance
• Autosomal Recessive Inheritance
• X-Linked Inheritance
• Reading a Pedigree
• NIPT
• CVS
• Amniocentesis
• Screening vs. Diagnostic Tests
• Common Prenatal Genetic Disorders (e.g., Trisomy 21, Trisomy 18, Trisomy 13)

One study technique I’d recommend

Unlike the earlier physiology chapters, genetics is best learned by working examples rather than rereading text. After reading the chapter, spend a few minutes drawing inheritance patterns and answering questions such as:

• “If both parents are carriers for an autosomal recessive disorder, what are the chances for each pregnancy?”
• “If a mother carries an X-linked recessive disorder, what are the chances her son will be affected?”
• “A patient has a positive NIPT for trisomy 21. What should I explain about what this result does—and does not—mean?”

Those scenarios mirror the kinds of conversations a midwife may actually have with clients.

A note about the chapter case study

The case study mentions NIPT and Duchenne muscular dystrophy. Those are excellent examples of where a midwife’s role is primarily education and support. Your responsibility is to understand the testing well enough to explain its purpose, strengths, and limitations, while recognizing when a patient should be referred to a maternal-fetal medicine specialist or genetic counselor for more specialized evaluation. That balance—solid foundational knowledge with appropriate referral—is an important part of good midwifery practice.