17.1

Chromosomes, genes and proteins

Cambridge IGCSE Biology (0610)  · Unit 17: Inheritance  · 12 flashcards

Chromosomes, genes and proteins is topic 17.1 in the Cambridge IGCSE Biology (0610) syllabus , positioned in Unit 17 — Inheritance , alongside Mitosis, Meiosis and Monohybrid inheritance.  In one line: Chromosomes are made of DNA. DNA contains genetic information in the form of genes, which determine an organism's traits.

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 record 4 explicit questions on this topic — though the concept underpins many adjacent topics, so it is tested far more often than that figure suggests.

The deck below contains 12 flashcards — 5 definitions, 5 key concepts and 2 process cards — covering the precise wording mark schemes reward.  Use the 5 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.

Key definition

Chromosomes made of, and what is their function

Chromosomes are made of DNA. DNA contains genetic information in the form of genes, which determine an organism's traits.

Example: the DNA in a human chromosome carries genes for eye color and height.

What the Cambridge 0610 syllabus says

2026-2028 syllabus, in our words

What the syllabus expects you to be able to do in this topic, in plain English. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks. For the exact wording, see the official syllabus (PDF).

  1. State State that chromosomes consist of DNA, and that DNA carries genetic information as genes.
  2. Define Define a gene: a section of DNA carrying the code for one protein.
  3. Define Define an allele: one of the different versions of a gene.
  4. Describe Describe how sex is inherited in humans, referring to the X and Y chromosomes.
  5. State State that the order of bases in a gene decides the order in which amino acids are joined to build a particular protein. You do not need details of nucleotide structure. Supplement
  6. Explain Explain that proteins take on different shapes because their amino acid sequences differ. Supplement
  7. Explain Explain that DNA controls what a cell does by controlling which proteins it makes; know three kinds: enzymes, membrane carriers and receptors for neurotransmitters. Supplement
  8. Explain Explain the steps in making a protein, covering only these points: the gene for the protein stays in the nucleus; messenger RNA (mRNA), a copy of the gene, is made in the nucleus and moves out into the cytoplasm; the mRNA travels through ribosomes; ribosomes join amino acids together to build the protein; the base sequence of the mRNA sets the exact order of the amino acids. Details of transcription and translation are not needed. Supplement
  9. Explain Explain that almost all body cells of an organism carry the same genes, yet in any one cell many genes are not expressed, because that cell makes only the particular proteins it needs. Supplement
  10. Describe Describe a haploid nucleus: one that holds just one set of chromosomes. Supplement
  11. Describe Describe a diploid nucleus: one that holds two sets of chromosomes. Supplement
  12. State State that a diploid cell has each type of chromosome as a pair, and that a human diploid cell has 23 pairs. Supplement
Definition Flip

What are chromosomes made of, and what is their function?

Answer Flip

Chromosomes are made of DNA. DNA contains genetic information in the form of genes, which determine an organism's traits.

Example: the DNA in a human chromosome carries genes for eye color and height.
Definition Flip

Define a gene.

Answer Flip

A gene is a length of DNA that codes for a specific protein.

Example: a gene can code for the production of insulin, a protein hormone involved in regulating blood sugar levels.
Definition Flip

Define an allele.

Answer Flip

An allele is an alternative form of a gene.

Example: the gene for eye color has alleles for blue eyes and brown eyes.
Key Concept Flip

How is sex determined in humans?

Answer Flip

Sex is determined by the X and Y chromosomes. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The Y chromosome carries the gene that determines maleness.

Key Concept Flip

How does the sequence of bases in a gene relate to protein structure?

Answer Flip

The sequence of bases in a gene determines the sequence of amino acids used to make a specific protein. This amino acid sequence dictates the protein's unique structure and function, like the enzyme amylase which breaks down starch.

Key Concept Flip

How do different amino acid sequences affect protein shape?

Answer Flip

Different sequences of amino acids cause a protein molecule to fold into different three-dimensional shapes. The shape of a protein is critical for its function;

Example: an enzyme's active site shape determines which substrate it can bind to.
Key Concept Flip

How does DNA control cell function?

Answer Flip

DNA controls cell function by directing the production of proteins. These proteins include enzymes (catalyze reactions), membrane carriers (transport molecules), and receptors for neurotransmitters (cell communication).

Key Concept Flip

Outline the process of protein synthesis.

Answer Flip

The gene for a protein remains in the nucleus. Messenger RNA (mRNA), a copy of the gene, is made in the nucleus and moves to the cytoplasm. The mRNA passes through ribosomes, which assemble amino acids into protein molecules based on the mRNA sequence.

Key Concept Flip

Why are not all genes expressed in every cell?

Answer Flip

Most body cells contain the same genes, but many are not expressed. Cells only make the specific proteins they need to perform their particular function.

Example: Pancreatic cells produce insulin, while skin cells do not.
Definition Flip

What is a haploid nucleus?

Answer Flip

A haploid nucleus contains a single set of chromosomes. Human gametes (sperm and egg cells) are haploid, containing 23 chromosomes each. They fuse during fertilization to form a diploid cell.

Definition Flip

What is a diploid nucleus?

Answer Flip

A diploid nucleus contains two sets of chromosomes. Most body cells (somatic cells) are diploid, with one set inherited from each parent. Human diploid cells have 23 pairs of chromosomes, totaling 46.

Key Concept Flip

How many pairs of chromosomes are in a human diploid cell?

Answer Flip

In a human diploid cell, there are 23 pairs of chromosomes, for a total of 46 chromosomes. These include 22 pairs of autosomes and one pair of sex chromosomes (XX or XY).

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16.6 Sexually transmitted infections 17.2 Mitosis

Key Questions: Chromosomes, genes and proteins

What are chromosomes made of, and what is their function?

Chromosomes are made of DNA. DNA contains genetic information in the form of genes, which determine an organism's traits.

Example: the DNA in a human chromosome carries genes for eye color and height.
Define a gene.

A gene is a length of DNA that codes for a specific protein.

Example: a gene can code for the production of insulin, a protein hormone involved in regulating blood sugar levels.
Define an allele.

An allele is an alternative form of a gene.

Example: the gene for eye color has alleles for blue eyes and brown eyes.
What is a haploid nucleus?

A haploid nucleus contains a single set of chromosomes. Human gametes (sperm and egg cells) are haploid, containing 23 chromosomes each. They fuse during fertilization to form a diploid cell.

What is a diploid nucleus?

A diploid nucleus contains two sets of chromosomes. Most body cells (somatic cells) are diploid, with one set inherited from each parent. Human diploid cells have 23 pairs of chromosomes, totaling 46.

Tips to avoid common mistakes in Chromosomes, genes and proteins

More topics in Unit 17 — Inheritance

Chromosomes, genes and proteins sits alongside these Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

17.2 Mitosis

9 flashcards
17.3 Meiosis

9 flashcards
17.4 Monohybrid inheritance

12 flashcards

Cambridge syllabus keywords to use in your answers

These are the official Cambridge 0610 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.

chromosome gene DNA allele nucleus base nucleotide double helix protein synthesis genetic code genome haploid diploid homologous

Key terms covered in this Chromosomes, genes and proteins deck

Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.

Chromosomes made of, and what is their function
A gene
An allele
Haploid nucleus
Diploid nucleus

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