Genes: A Very Short Introduction

Citation

Slack, J. (2023). Genes: A Very Short Introduction (2nd ed.). Oxford University Press.

Chapter Summary

This second edition, published in April 2023, runs to about 160 pages: a preface and list of illustrations, six chapters and a conclusion, further reading, a glossary and an index. The publisher describes it as fully updated, with new sections on the CRISPR method of targeted genetic modification, on DNA profiling and on what ancient DNA has revealed about human ancestry. The book is organized less as a tour of mechanisms than as an account of the different things biologists and social scientists mean by "gene", which the conclusion draws together.

Chapter 1: Genes before 1944

The opening chapter follows the idea of the gene from Mendel's work on hereditary factors in 1866 to Oswald Avery's 1944 paper identifying the "transforming principle" with DNA. It shows that two separate lines of work, experimental study of heredity and the chemistry of DNA, came together in the mid-twentieth century to create molecular biology, and contrasts them with breeders' earlier, uninformed notions of "blood lines".

Chapter 2: Genes as DNA

After 1944 a series of discoveries built modern molecular biology, beginning with the double helix, which showed how DNA could act as the genetic material. The chapter describes the structure of genes and explains "genome" and "genomics"; it then covers the discovery of gene regulation (including mechanisms involving DNA methylation) in the 1970s and 1980s, the genetic control of embryonic development in the 1980s and 1990s, the human genome sequence completed in 2003, and methods for genetically modifying microorganisms, plants and animals, the setting for the new material on CRISPR.

Chapter 3: Mutations and gene variants

All gene variants begin as mutations, though most of those in any individual were inherited rather than newly arisen. The chapter explains why only mutations in reproductive cells are passed on, uses cystic fibrosis, haemophilia and achondroplasia as examples of single-gene diseases inherited by simple Mendelian rules, and explains cancer as the accumulation of several mutations in one body cell, with inherited predisposition explained as reducing the number of new mutations needed.

Chapter 4: Genes as markers

Most genetic variation does not change what genes do, but it is still informative. The chapter covers DNA fingerprinting in forensics, establishing paternity and other family relationships, and the recent possibility of inferring something of a person's appearance from DNA. It then turns to human migration, using mitochondrial DNA for the female line and the Y chromosome for the male line, the contribution of ancient DNA from archaeological specimens, what population differences reveal about whether perceived race has a biological basis, and consumer ancestry kits.

Chapter 5: Genes of small effect

Many traits depend on numerous genes, each with a small effect. The chapter shows how this assumption has guided animal and plant breeding and why it has been controversial when applied to people. It discusses heritability, defined as the proportion of variation in a population attributable to genetic variation, for human height, serious mental illness and IQ, together with genome-wide association studies and the growing ability to predict an individual's risk of specific diseases from the variants they carry.

Chapter 6: Genes in evolution

This chapter examines what the gene concept has done to evolutionary theory. It separates natural selection, which creates novelty, from neutral evolution by genetic drift, which accounts for much change in DNA sequence and makes it possible to classify organisms from their DNA. It discusses the puzzles of sex and altruism, where what spreads gene variants seems to benefit the group at the individual's cost, and ends with evolutionary psychology, the school that holds that universal features of human belief and behaviour evolved biologically.

Conclusion: the varied concepts of the gene

The conclusion sets side by side the senses of "gene" used through the book: the molecular biologist's DNA sequence with a defined function; variants used as markers in population and ancestry studies; the presumed genes of small effect in quantitative genetics; presumed variants affecting behaviour in evolutionary theory; and the genetic basis of universal attributes claimed in evolutionary psychology.

Key Concepts

Chapters 1–2: what a gene is

• Transforming principle: the substance Avery identified with DNA in 1944, linking the gene to a chemical.
• Genome and genomics: an organism's complete DNA, and its study as a whole.
• Gene regulation and DNA methylation: the control of when genes are active, including chemical marking of DNA.
• Genetic modification and CRISPR: altering the genes of organisms, now including targeted editing.

Chapters 3–4: variation

• Gene variant: an alternative form of a gene, originally produced by mutation and usually inherited.
• Germline versus somatic mutation: only changes in reproductive cells are passed to offspring.
• Genetic marker: a variant that does not alter function but identifies individuals or traces lineages.
• Mitochondrial DNA and Y chromosome: markers for the female and male lines of descent.

Chapters 5–6 and Conclusion: populations and evolution

• Heritability: the share of variation in a trait across a population due to genetic variation, not the extent to which a trait is "genetic" in an individual.
• Genome-wide association study (GWAS): a search across the genome for variants associated with a trait or disease.
• Genetic drift and neutral evolution: random change in variant frequencies, independent of selection.
• Concepts of the gene: the book's closing distinction between molecular, marker, quantitative and evolutionary meanings of the word.

Critical Analysis

Strengths

• Clarifies what "gene" means. The book's organizing idea, stated in the publisher's description and made explicit in the conclusion, is that molecular biologists, population biologists and social scientists use the word differently. That distinction helps students reading across genetics, evolution and the social sciences avoid talking past one another.
• Addresses contested topics directly. Heritability and IQ, serious mental illness, the biological basis of race and evolutionary psychology all receive attention, framed through definitions (heritability as a population measure) rather than slogans.
• Updated second edition. The 2023 edition adds CRISPR, DNA profiling and ancient-DNA work on human ancestry, so the applications are more current than in the 2014 first edition.
• Reference aids. A glossary and a list of illustrations support readers without a science background, and the publisher's endorsements include Steve Jones's verdict that the book is "short, sharp, and to the point".

Limitations

• Mechanisms are compressed. Gene structure, gene regulation, developmental control, genome sequencing and genetic modification all fall within a single chapter, "Genes as DNA". Students who need the molecular processes in detail must turn to a textbook.
• Little formal genetics. Mendelian inheritance appears historically and through single-gene diseases, but the contents show no treatment of crosses, linkage or mapping, the problem-solving core of a genetics course, and there are no exercises.
• Brief by design. At about 160 pages, topics such as GWAS, drift and evolutionary psychology receive a section each; the further reading list is the route onward.

Where It Fits in the Course

This is the least technical book in the genetics course list and works as background reading rather than a course text. Alison Thomas's Introducing Genetics: From Mendel to Molecules is the gentler of the textbooks: a short first university introduction moving from Mendel and chromosomes to molecular genetics, mutation and populations, with the working explanations that Slack's essay-style chapters do not attempt. Griffiths and colleagues' Introduction to Genetic Analysis and Snustad and Simmons's Principles of Genetics are the comprehensive main texts, the first taught strongly through problem solving.

Two specialized books continue particular chapters. Chapters 5 and 6 (heritability, drift and selection) lead naturally into Hartl and Clark's Principles of Population Genetics, a standard theoretical treatment of how allele frequencies change. Chapter 2's account of genomes leads into Terry Brown's Genomes 5, which treats genetics at the level of whole genomes and their sequencing, expression and evolution. Read Slack first, or alongside the main textbook, for the conceptual map.

How to Use This Book

The book suits readers with school biology or none: students about to start genetics, students in psychology, anthropology, law or the social sciences who meet claims about genes and heritability, and general readers. It can be read in a few sittings.

A practical plan:

• Read in order. Chapters 1–2 establish what a gene is and how that answer emerged; later chapters build on them.
• Take Chapter 5 slowly. Heritability is the concept most often misunderstood outside biology. Write down the population-level definition and check how each example (height, mental illness, IQ) uses it.
• Use Chapter 4 for applied interests. Forensics, paternity, ancestry testing and the question of race are concentrated here.
• Finish with the conclusion, then reread whichever chapter corresponds to the sense of "gene" most relevant to the course.

Alongside the book, students should practise Mendelian crosses and pedigree problems from a textbook such as Thomas or Griffiths, since the VSI supplies the concepts but no exercises. The glossary is useful as a quick check while reading other material.