AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
When a cell divides to form gametes: • copies of the genetic information…
Full specification wording
Meiosis: When a cell divides to form gametes: • copies of the genetic information are made • the cell divides twice to form four gametes, each with a single set of chromosomes • all gametes are genetically different from each other.
Meiosis is the two-stage division that makes gametes.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 3 of 7
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Meiosis is the two-stage division that makes gametes. Before division begins, the DNA is replicated so each chromosome becomes two identical chromatids, giving copies of the genetic information. The cell then divides twice: the first division separates homologous chromosomes, and the second separates the sister chromatids. One starting cell therefore yields four gametes, each with a single set of chromosomes (haploid). Because homologous chromosomes are shuffled independently and crossing over exchanges sections between them, each gamete receives a different combination of alleles, so all four gametes are genetically different. In humans the diploid number is 46, so each gamete has 23 chromosomes; at fertilisation two haploid gametes restore the diploid number.
What earns the marks
- DNA replication occurs before division, producing two identical copies (chromatids) of each chromosome.
- Two divisions occur in sequence, so one cell produces four gametes rather than two.
- Each gamete contains one chromosome from each homologous pair, described as a single (haploid) set.
- Gametes differ genetically because of independent assortment of homologous chromosomes and crossing over between them.
- In humans, body cells have 46 chromosomes and gametes have 23, so fertilisation restores 46.
Common mistakes and how to put them right
Saying the cell divides once and produces two gametes.
Put it right: Meiosis involves two divisions and produces four gametes.
Confusing meiosis with mitosis.
Put it right: Mitosis produces genetically identical diploid cells for growth, whereas meiosis produces genetically varied haploid gametes.
Stating that gametes are identical clones.
Put it right: Independent assortment and crossing over make every gamete genetically different.
Exam tips
- Use the terms haploid and diploid precisely, linking haploid to gametes and diploid to the fertilised cell.
- When asked to explain variation, name both independent assortment and crossing over rather than writing only 'mixing of genes'.
- Check the number of divisions and the number of products in your answer, because these are the easiest facts to state incorrectly.
Try the lesson
The start of the Meiosis: When a cell divides to form gametes: • copies of the genetic information are made • the cell divides twice to form four gametes, each with a single set of chromosomes • all gametes are genetically different from each other. lesson, made from checked teaching notes for this specification point.
Have a go first
How many gametes are produced from one parent cell during meiosis, and how many sets of chromosomes does each contain?
Listen
Meiosis is the two-stage division that makes gametes. Before division begins, the DNA is replicated so each chromosome becomes two identical chromatids, giving copies of the genetic information. The cell then divides twice: the first division separates homologous chromosomes, and the second separates the sister chromatids. One starting cell therefore yields four gametes, each with a single set of chromosomes (haploid). Because homologous chromosomes are shuffled independently and crossing over exchanges sections between them, each gamete receives a different combination of alleles, so all four gametes are genetically different. In humans the diploid number is 46, so each gamete has 23 chromosomes; at fertilisation two haploid gametes restore the diploid number. A strong answer earns marks for these points. DNA replication occurs before division, producing two identical copies (chromatids) of each chromosome. Two divisions occur in sequence, so one cell produces four gametes rather than two. Each gamete contains one chromosome from each homologous pair, described as a single (haploid) set. Gametes differ genetically because of independent assortment of homologous chromosomes and crossing over between them. A common slip: Saying the cell divides once and produces two gametes. Instead, meiosis involves two divisions and produces four gametes. Exam tip: Use the terms haploid and diploid precisely, linking haploid to gametes and diploid to the fertilised cell.
See it
Key words
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DNA replication before division
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Two-stage nuclear division
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Haploid gamete formation
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See every definition
- DNA replication before division
- Before division begins, the DNA is replicated so each chromosome becomes two identical chromatids, giving copies of the genetic information.
- Two-stage nuclear division
- The cell divides twice: the first division separates homologous chromosomes, and the second separates the sister chromatids.
- Haploid gamete formation
- One starting cell yields four gametes, each with a single set of chromosomes.
Label the diagram
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1Box 1
2Box 2
3Box 3
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