Chromosomes, DNA and Genes Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Understanding the structure and organisation of genetic material in cells, including how DNA is organised into chromosomes and the relationship between...

• Explain the relationship between chromosomes, DNA and genes in cells
• Describe the structure and location of chromosomes in body cells
• Compare the chromosome arrangement in body cells versus gametes
• Apply knowledge of chromosome pairs to explain inheritance patterns

Key ideas to keep in view

Use this lesson to stay inside B5.1 Inheritance while connecting the detail back to the wider B5: Genes, inheritance and selection topic.

• B5: Genes, inheritance and selection
• B5.1 Inheritance
• GCSE OCR Foundation Biology

Lesson notes preview

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.
• The chemical molecule that stores genetic information. Made of two strands twisted into a double helix shape.
• A section of DNA that codes for one specific characteristic, such as eye colour or blood group.
• A structure made of tightly coiled DNA that carries hundreds or thousands of genes.
• 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.

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.