AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Chromosomes: In body cells the chromosomes are normally found in pairs.
Body cells are diploid: they contain two copies of each chromosome, one inherited from each parent.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 3 of 3
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Body cells are diploid: they contain two copies of each chromosome, one inherited from each parent. In humans this means 46 chromosomes arranged as 23 pairs, and the two members of a pair carry the same genes in the same order, though they may carry different versions called alleles. A pair is not joined together permanently; the chromosomes are separate structures that happen to match in size and gene content. Gametes are the exception, because they are haploid and carry one chromosome from each pair, so fertilisation restores the diploid number. A reliable method is to count chromosomes, halve the number to find the pairs, and remember that a pair means two matching chromosomes, not two identical DNA molecules. This pairing is the basis of inheritance and of why characteristics can vary between siblings.
What earns the marks
- States that body cells are diploid, containing two copies of each chromosome.
- Explains that one chromosome of each pair comes from each parent.
- Uses the human example of 46 chromosomes arranged as 23 pairs.
- Distinguishes paired chromosomes from gametes, which carry a single set.
- Links paired chromosomes to alleles, the different versions of a gene that a pair may carry.
Common mistakes and how to put them right
Saying body cells contain 23 chromosomes.
Put it right: They contain 46 chromosomes arranged as 23 pairs.
Describing paired chromosomes as physically joined.
Put it right: They are separate matching chromosomes, not fused structures.
Assuming the two chromosomes of a pair are identical.
Put it right: They carry the same genes but may carry different alleles.
Exam tips
- Quote the diploid number and the pair number together, for example 46 chromosomes as 23 pairs, to show both facts clearly.
- If a question contrasts body cells with gametes, state the chromosome number in each to make the difference explicit.
- Use the term allele only when referring to different versions of the same gene, so the vocabulary stays precise.
Try the lesson
The start of the Chromosomes: In body cells the chromosomes are normally found in pairs. lesson, made from checked teaching notes for this specification point.
Have a go first
How are chromosomes normally arranged in a human body cell?
Listen
Body cells are diploid: they contain two copies of each chromosome, one inherited from each parent. In humans this means 46 chromosomes arranged as 23 pairs, and the two members of a pair carry the same genes in the same order, though they may carry different versions called alleles. A pair is not joined together permanently; the chromosomes are separate structures that happen to match in size and gene content. Gametes are the exception, because they are haploid and carry one chromosome from each pair, so fertilisation restores the diploid number. A reliable method is to count chromosomes, halve the number to find the pairs, and remember that a pair means two matching chromosomes, not two identical DNA molecules. This pairing is the basis of inheritance and of why characteristics can vary between siblings. A strong answer earns marks for these points. States that body cells are diploid, containing two copies of each chromosome. Explains that one chromosome of each pair comes from each parent. Uses the human example of 46 chromosomes arranged as 23 pairs. Distinguishes paired chromosomes from gametes, which carry a single set. A common slip: Saying body cells contain 23 chromosomes. Instead, they contain 46 chromosomes arranged as 23 pairs. Exam tip: Quote the diploid number and the pair number together, for example 46 chromosomes as 23 pairs, to show both facts clearly.
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Key words
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Diploid and haploid cells
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Inheritance from both parents
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Alleles and genetic variation
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Chromosome number in humans
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See every definition
- Diploid and haploid cells
- Body cells are diploid, containing two copies of each chromosome, while gametes are haploid and carry one chromosome from each pair.
- Inheritance from both parents
- One chromosome of each pair is inherited from each parent, and this pairing is the basis of inheritance.
- Alleles and genetic variation
- The two members of a pair carry the same genes in the same order, though they may carry different versions called alleles, which is why characteristics can vary between siblings.
- Chromosome number in humans
- In humans this means 46 chromosomes arranged as 23 pairs.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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