GCSE Biology Revision — Chromosomes & Genes
Revise Chromosomes & Genes for GCSE Biology. Step-by-step explanation, worked examples, common mistakes and exam-style practice aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), Pearson Edexcel International, OxfordAQA International, SQA, IB, AP.
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What is Chromosomes & Genes?
Chromosomes are long, coiled molecules of DNA found in the nucleus of eukaryotic cells, carrying a large number of genes. Humans have 23 pairs of chromosomes in each body cell. A gene is a section of DNA that contains the code for making a specific protein.
Board notes: Covered by all major boards (AQA, Edexcel, OCR). The relationship between DNA, genes, and chromosomes is a fundamental concept.
Step-by-step explanationWorked examples
Worked example 1: Core method
A typical human body cell, like a skin cell, has 46 chromosomes in its nucleus, arranged as 23 pairs. Pair 23 determines sex (XX for female, XY for male), while the other 22 pairs are autosomes. Each chromosome contains hundreds or thousands of genes, each coding for a specific protein.
Worked example 2: Exam variation
Now change one detail in the question and keep the same structure: name the Chromosomes & Genes idea being tested, show the method or evidence, then explain why it answers the command word. This helps GCSE Biology students avoid memorising one surface pattern.
Worked example 3: Mark-scheme check
Finish by checking the answer against marks: one point for the correct Chromosomes & Genes idea, one for accurate working or evidence, and one for a precise final statement. If any step is vague, rewrite it before moving to timed practice.
Mini lesson for Chromosomes & Genes
1. Understand the core idea
Chromosomes are long, coiled molecules of DNA found in the nucleus of eukaryotic cells, carrying a large number of genes. Humans have 23 pairs of chromosomes in each body cell.
Can you explain Chromosomes & Genes without copying the notes?
2. Turn it into marks
A typical human body cell, like a skin cell, has 46 chromosomes in its nucleus, arranged as 23 pairs. Pair 23 determines sex (XX for female, XY for male), while the other 22 pairs are autosomes.
Underline the method, evidence, or command-word move that would earn credit in GCSE Inheritance, Variation & Evolution.
3. Fix the likely mark leak
Watch for this mistake: Confusing chromosomes and chromatids. A chromosome can consist of one or two identical sister chromatids, which are copies made during DNA replication before a cell divides.
Write one correction rule before doing another practice question.
Practise this topic
Start with low-focus cards for Chromosomes & Genes, then move into full exam-style practice when you want the heavier session.
Mini quiz: Chromosomes & Genes
Three quick checks for revision practice. They are original StudyVector prompts, not official exam-board questions.
Question 1
In one GCSE sentence, explain what Chromosomes & Genes is testing.
Answer: Chromosomes are long, coiled molecules of DNA found in the nucleus of eukaryotic cells, carrying a large number of genes. Humans have 23 pairs of chromosomes in each body cell.
Mark focus: Precise definition and topic focus.
Question 2
A Chromosomes & Genes question uses an unfamiliar context. What should the answer do before adding detail?
Answer: It should name the process, variable, equation, particle model, or evidence being tested, then explain the result using precise scientific vocabulary.
Mark focus: Method selection and command-word control.
Question 3
A student makes this mistake: "Confusing chromosomes and chromatids. A chromosome can consist of one or two identical sister chromatids, which are copies made during DNA replication before a cell divides." What should their next repair task be?
Answer: Do one Chromosomes & Genes question and review the mistake type.
Mark focus: Error correction and next-step practice.
Chromosomes & Genes flashcards
Core idea
What is the main idea in Chromosomes & Genes?
Chromosomes are long, coiled molecules of DNA found in the nucleus of eukaryotic cells, carrying a large number of genes. Humans have 23 pairs of chromosomes in each body cell.
Common mistake
What mistake should you avoid in Chromosomes & Genes?
Confusing chromosomes and chromatids. A chromosome can consist of one or two identical sister chromatids, which are copies made during DNA replication before a cell divides.
Practice
What is one useful practice task for Chromosomes & Genes?
Answer one Chromosomes & Genes question and review the mistake type.
Exam board
How should you use board notes for Chromosomes & Genes?
Covered by all major boards (AQA, Edexcel, OCR). The relationship between DNA, genes, and chromosomes is a fundamental concept.
Common mistakes
- 1Confusing chromosomes and chromatids. A chromosome can consist of one or two identical sister chromatids, which are copies made during DNA replication before a cell divides.
- 2Thinking that the number of chromosomes indicates an organism's complexity. Chromosome number varies widely between species and is not a reliable indicator of complexity.
- 3Forgetting that chromosomes in body cells come in pairs. Humans have 23 homologous pairs – one chromosome in each pair is inherited from each parent.
Chromosomes & Genes exam questions
Exam-style questions for Chromosomes & Genes with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), Pearson Edexcel International, OxfordAQA International, SQA, IB, AP specifications.
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Step-by-step method
Step-by-step explanation
4 steps · Worked method for Chromosomes & Genes
Core concept
Chromosomes are long, coiled molecules of DNA found in the nucleus of eukaryotic cells, carrying a large number of genes. Humans have 23 pairs of chromosomes in each body cell. A gene is a section of …
Frequently asked questions
How many chromosomes do humans have?
Human body cells have 46 chromosomes, arranged as 23 pairs. Gametes (sperm and egg cells) are haploid and have only 23 single chromosomes.
What is the relationship between a gene and a protein?
A gene is a sequence of DNA that provides the instructions for assembling amino acids in a specific order to create a particular protein. This protein then carries out a specific function in the body.