AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
Meiosis produces daughter cells that are genetically different from each…
Full specification wording
Genetic diversity can arise as a result of mutation or during: Meiosis produces daughter cells that are genetically different from each other.
Meiosis produces genetically distinct daughter cells via two key mechanisms.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 6 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Meiosis produces genetically distinct daughter cells via two key mechanisms. First, independent segregation occurs at metaphase I. Homologous chromosome pairs align randomly on the equator; which chromosome goes to which pole is independent of other pairs. For example, humans have 23 pairs, yielding $2^{23}$ (over 8.3 million) possible chromosome combinations. Second, crossing over happens in prophase I. Homologous chromosomes form bivalents and chromatids twist at chiasmata, exchanging equivalent sections of DNA. Because homologues carry different alleles, this creates entirely new combinations of alleles on a single chromosome, increasing genetic diversity.
What earns the marks
- Homologous chromosomes pair up to form bivalents during prophase I.
- Crossing over occurs at chiasmata, exchanging equivalent lengths of chromatids between homologous chromosomes.
- Independent segregation of homologous chromosomes occurs randomly at the equator during metaphase I.
- The formula $2^n$ can be used to calculate the number of possible chromosome combinations, where $n$ is the number of homologous pairs.
Common mistakes and how to put them right
Stating that crossing over occurs between sister chromatids.
Put it right: Specify that crossing over occurs between non-sister chromatids of homologous chromosomes.
Including random fertilisation as a mechanism of meiosis.
Put it right: Random fertilisation increases genetic variation in a population but occurs after meiosis, not during it.
Confusing genes and alleles when describing crossing over.
Put it right: State that crossing over produces new combinations of alleles, not new genes.
Exam tips
- When asked how meiosis creates genetic variation, focus strictly on independent segregation and crossing over; do not include random fertilisation unless the question asks about variation in the whole life cycle.
- Always conclude descriptions of meiotic variation by explicitly stating that these processes produce 'new combinations of alleles'.
Try the lesson
The start of the Genetic diversity can arise as a result of mutation or during: Meiosis produces daughter cells that are genetically different from each other. lesson, made from checked teaching notes for this specification point.
Have a go first
Which two processes during meiosis are primarily responsible for producing daughter cells that are genetically different from each other?
Listen
Meiosis produces genetically distinct daughter cells via two key mechanisms. First, independent segregation occurs at metaphase I. Homologous chromosome pairs align randomly on the equator; which chromosome goes to which pole is independent of other pairs. For example, humans have 23 pairs, yielding 2^{23} (over 8.3 million) possible chromosome combinations. Second, crossing over happens in prophase I. Homologous chromosomes form bivalents and chromatids twist at chiasmata, exchanging equivalent sections of DNA. Because homologues carry different alleles, this creates entirely new combinations of alleles on a single chromosome, increasing genetic diversity. A strong answer earns marks for these points. Homologous chromosomes pair up to form bivalents during prophase I. Crossing over occurs at chiasmata, exchanging equivalent lengths of chromatids between homologous chromosomes. Independent segregation of homologous chromosomes occurs randomly at the equator during metaphase I. The formula 2^n can be used to calculate the number of possible chromosome combinations, where n is the number of homologous pairs. A common slip: Stating that crossing over occurs between sister chromatids. Instead, Specify that crossing over occurs between non-sister chromatids of homologous chromosomes. Exam tip: When asked how meiosis creates genetic variation, focus strictly on independent segregation and crossing over; do not include random fertilisation unless the question asks about variation in the whole life cycle.
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Key words
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independent segregation
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crossing over
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new combinations of alleles
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genetic variation
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See every definition
- independent segregation
- Homologous chromosome pairs align randomly on the equator at metaphase I, and which chromosome goes to which pole is independent of other pairs.
- crossing over
- In prophase I, homologous chromosomes form bivalents and chromatids twist at chiasmata, exchanging equivalent sections of DNA.
- new combinations of alleles
- Because homologues carry different alleles, crossing over creates entirely new combinations of alleles on a single chromosome, increasing genetic diversity.
- genetic variation
- Meiosis produces daughter cells that are genetically different from each other, and crossing over increases genetic diversity.
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