HG101

Understand Human Genetics with Diagrams and Exercises

An introductory course that uses diagrams and plain language to organize DNA, genes, chromosomes, meiosis, inheritance patterns, family history, and how to read genetic test results. It is written so that even someone who has not yet studied high-school biology in depth can follow along through diagrams and examples.

Plain vocabulary 42 questions in total Graded in-browser Saved to localStorage

Time

3–4 hours

Question count

42 questions

Format

7 chapters + term cards + short exercises

Cost

Free

Important note: This course is for education. It cannot be used to judge individual symptoms, pregnancies, family histories, or test results. For real-world decisions, please consult a medical professional or a genetic counselor.

What this edition assumes

This edition is written so that you can read it if the words "cell," "nucleus," and "chromosome" ring a faint bell. You do not need to have covered them in detail at school yet. The required vocabulary is collected up front and then repeated in each chapter.

Formulas are kept to a minimum, and probability is restricted to what a 2×2 table or small numbers can handle. Rather than treating human genetics as a story of "fate being decided," we practice reading it by separating which unit are we talking about from how certain the claim is.

Glossary to read first

DNA (deoxyribonucleic acid)

The information string that acts as the body's blueprint. Think of it as a sequence written in four letters: A, T, G, and C.

Gene

A specific stretch of DNA that is involved in a function of the body. Like a single "item" inside an instruction manual.

Chromosome

The unit that results when long DNA is folded and packaged. It is not the same thing as DNA; it is the package DNA sits inside.

Genome

All of the DNA that an organism carries. Not a single gene but the whole instruction manual.

Meiosis

The cell division that produces gametes such as eggs and sperm. It halves the chromosome number.

Gamete

Eggs and sperm. Before fertilization, they carry half the chromosome number of a body cell.

Allele

Slightly different versions of a gene that sit at the same location. They are often written with symbols such as A and a.

Dominant

A form whose phenotype tends to appear with just one copy. "Dominant" does not mean "stronger" or "better."

Recessive

A form whose phenotype typically appears only when two copies are present. "Recessive" does not mean "weaker" or "inferior."

Carrier

A person who has one copy of a disease-related variant and can pass it to the next generation. The exact meaning shifts a little depending on context.

Genotype

The combination of alleles a person carries. Information on the blueprint side.

Phenotype

The traits that actually show up. Related to genotype, but also affected by the environment.

Variant

A neutral word for differences in DNA sequence. Some have almost no effect; others are linked to disease.

Autosome

Any chromosome that is not a sex chromosome. Humans have 22 pairs.

X-linked

A pattern where the change sits on the X chromosome, so its inheritance looks a little different from that of an autosome.

Mitochondrial DNA (mtDNA)

DNA inside the mitochondria. For this introductory course we treat it as passed from mother to child.

Multifactorial

A view in which multiple genetic factors and environmental factors stack up to determine the outcome. A single gene cannot explain it.

Genetic predisposition

An increased tendency to develop a disease. It is not a certainty — it means the risk is higher.

Penetrance

The fraction of people with the same variant who actually show the phenotype.

Variable expressivity

The idea that even with the same variant, the severity or appearance of symptoms can differ between people.

Family health history

A record of diseases and health conditions seen in the family. It reflects not only genetics but also lifestyle and environment.

VUS (variant of uncertain significance)

A variant whose pathogenic meaning is not yet determined.

Five viewpoints we keep reusing

Each chapter also reprints the viewpoint it leans on. It is fine to skim this list on first read.

1. Align the units

Do not lump DNA, gene, chromosome, and genome together — say which one you mean.

2. Watch where the count halves

Follow the flow in which meiosis produces gametes and fertilization brings the two copies back together.

3. Separate the inheritance patterns

Do not mix up autosomal, X-linked, mitochondrial, and de novo.

4. Check what the probability is conditional on

Distinguish "for each pregnancy" from "given that we already know such-and-such."

5. Weigh results differently

A Mendelian ratio, a polygenic risk, and an unsettled piece of information such as a VUS must not be treated as if they carried the same weight.

Chapter overview

1 DNA, genes, and chromosomes 5 questions. Build the habit of talking about DNA, genes, chromosomes, and the genome as separate units. 2 Meiosis and gametes — why the count halves and why things mix a little 6 questions. Follow how gametes end up with half the chromosomes and how recombination mixes things gradually. 3 Mendelian inheritance — reading dominant, recessive, and carriers as probabilities 6 questions. Track autosomal dominant and recessive patterns through a Punnett square (2×2 table). 4 Sex-linked, mitochondrial, and chromosomal inheritance 6 questions. Organize the non-Mendelian patterns and the cases where the chromosome count itself differs. 5 Traits a single gene cannot explain — polygenic, penetrance, and environmentMost important 6 questions. Nail down the cases a single gene cannot explain, together with the ideas of penetrance and variable expressivity. This is the most conceptually demanding chapter of the course; the relative-vs-absolute-risk distinction it teaches keeps paying off in the other chapters. 6 Genetic testing and family history 5 questions. Cover types of tests, the VUS, and how to organize a family history — stopping just before individual judgment. 7 Comprehension check 8 questions. Review probability and definitions across cases.

Tips for studying

One pass through the glossary up front is enough. Every chapter also re-explains the terms you need.
For probability questions, always sketch the 2×2 table before typing the answer.
Re-reading the polygenic and penetrance chapter (Chapter 5) right before Chapter 7 makes the comprehensive exercises feel much calmer.

Prerequisites before you start

A faint familiarity with the words "cell," "nucleus," and "chromosome" is enough.
English-language technical terms are supplied in parentheses only where they help.
No external libraries — this runs on static HTML / CSS / JavaScript alone.