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Human body cells have 46 chromosomes arranged in 23 pairs. Free GCSE AQA Biology notes with key terms and 14 questions answered.
Chromosomes, DNA and Genes is part of Cell division in GCSE AQA Higher Biology.
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Human body cells have 46 chromosomes arranged in 23 pairs. Free GCSE AQA Biology notes with key terms and 14 questions answered.
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Use this lesson to stay inside Cell division while connecting the detail back to the wider Cell biology topic.
Read the core explanations from Chromosomes, DNA and Genes before testing yourself from memory.
Your body contains the instructions for everything about you - your eye colour, height, blood type, even how your enzymes work. But where are these instructions stored, and how are they organised?
Think of your genetic information like a massive library. The building is your cell nucleus. Inside are filing cabinets called chromosomes. Each filing cabinet contains thousands of instruction manuals called genes. The paper these manuals are written on? That's DNA.
Trap: Many students think genes and chromosomes are the same thing. Actually, one chromosome contains many genes - like one filing cabinet containing many instruction manuals.
Let's zoom in from the biggest structure to the smallest. In your cell nucleus, you'll find 46 chromosomes. Each chromosome is made of one incredibly long DNA molecule, coiled up tightly to fit.
Along this DNA molecule are thousands of genes - specific sections that code for particular characteristics. Think of it like this: if DNA is a recipe book, then genes are individual recipes, and chromosomes are the chapters that group related recipes together.
The key relationship is: Nucleus contains chromosomes → Chromosomes are made of DNA → DNA contains genes. Each level contains the next, like Russian dolls.
Here's where it gets interesting. Human body cells don't just have 46 random chromosomes scattered about. They have 23 pairs - that's 46 chromosomes arranged in matching couples.
Each pair consists of two chromosomes that carry genes for the same characteristics. For example, both chromosomes in pair 1 have genes for eye colour - but one might code for brown eyes while the other codes for blue eyes.
Why pairs? Because you inherited one chromosome from each parent. Your mum gave you 23 chromosomes, your dad gave you 23 chromosomes, and they paired up to give you 23 pairs (46 total).
Trap: Students often think humans have 23 chromosomes total. Actually, we have 23 pairs = 46 chromosomes in body cells. Only gametes (sex cells) have 23 individual chromosomes.
Let's put this together with a concrete example. Imagine you're looking at chromosome pair 15 in one of your muscle cells.
Worked example: Tracing Genetic Information from Cell to Gene
Follow the genetic information for eye colour from the cell nucleus down to the specific gene.
Answer: One gene for eye colour exists at the same position on both chromosomes in pair 15
This hierarchy explains why you might have brown eyes like your dad but your sister has blue eyes like your mum - you both got different versions of the eye colour gene from your parents.
Examiners love to test whether you understand the relationship between chromosomes, DNA and genes. Here are the mistakes that cost students marks, and how to avoid them.
Exam depth extension: In chromosomes, dna and genes, connect the genetic filing system to the hierarchy of genetic information using clear cause-and-effect statements. When you explain biological processes, include what changes, why it changes, and the consequence for cells, organisms, or populations. If calculations appear, show each step, include units, and end with a sentence that interprets the result in biological context.
Mark-winning phrases: When describing chromosome structure, always mention that chromosomes are 'made of DNA molecules' and that they 'carry many genes'. This shows you understand the relationship.
For 'explain' questions about inheritance, remember to mention that 'chromosomes exist in pairs in body cells' - this sets up why offspring get characteristics from both parents.
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-20.
Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Human body cells have 46 chromosomes arranged in 23 pairs. One chromosome of each pair comes from each parent, so 23 come from the mum and 23 from the dad. Only gametes, or sex cells, have 23 individual chromosomes.
A gene is a specific section of a DNA molecule that codes for a particular characteristic. Each chromosome carries thousands of genes, so one chromosome contains many genes, like one filing cabinet containing many instruction manuals.
Chromosomes are found in the cell nucleus. A human body cell nucleus contains 46 chromosomes, each made of one incredibly long DNA molecule coiled up tightly to fit, and each carrying many genes.
Humans have 23 pairs of chromosomes, which is 46 chromosomes in body cells. One chromosome of each pair is inherited from each parent. Only gametes (sex cells) have 23 individual chromosomes.
A homologous pair is two chromosomes that carry the same genes in the same positions but may have different versions (alleles) of those genes. Human body cells have 23 such pairs, with one chromosome of each pair inherited from each parent.
A chromosome is made of tightly coiled DNA, with each chromosome being one long DNA molecule coiled up to fit in the nucleus. Along this DNA are hundreds or thousands of genes, each coding for a particular characteristic.
Chromosomes are made of DNA, and DNA contains genes. Each chromosome is one incredibly long DNA molecule coiled up tightly in the nucleus, and along it are thousands of genes, which are specific sections that code for particular characteristics.
Chromosomes come in pairs because one chromosome of each pair is inherited from each parent. Both chromosomes in a pair carry genes for the same characteristics, such as eye colour, but one might code for brown eyes while the other codes for blue eyes.
Human chromosomes come from both parents: the mother gives 23 chromosomes and the father gives 23 chromosomes, and they pair up to give 23 pairs, or 46 in total. This is why offspring get characteristics from both parents.
A human gamete (sex cell) has 23 individual chromosomes, half the number in body cells. Body cells have 46 chromosomes arranged in 23 pairs, because 23 come from the mother and 23 from the father.
The order from biggest to smallest is nucleus, chromosome, DNA, gene: the nucleus contains chromosomes, chromosomes are made of DNA, and DNA contains genes. Each level contains the next, like Russian dolls.
Genes and chromosomes are not the same thing. One chromosome contains many genes, like one filing cabinet containing many instruction manuals, whereas a gene is a section of DNA that codes for one specific characteristic.
Two people in one family can have different eye colours because each child gets different versions of the eye colour gene from their parents. One child might inherit the version for brown eyes from their dad while another inherits the version for blue eyes from their mum.
A gene is found at a specific location on the DNA of a chromosome, and the same gene sits at the same position on both chromosomes in a pair. For example, the eye colour gene is at the same position on both chromosomes in pair 15.