Read How Meiosis Creates Variation
Meiosis both separates alleles and reshuffles linked genetic material.
Meiotic Variation is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Separate homologues
Homologous chromosomes segregate at anaphase I, separating alleles on the homologues even when crossing over does not occur.
Create new combinations
Crossing over in prophase I of germ-cell meiosis recombines alleles. Heritable new variation comes from germline events, unlike most somatic mutations.
Why meiosis II can differ from mitosis
Crossing over in prophase I can leave sister chromatids genetically non-identical; meiosis II may therefore send different chromatids to its daughter cells. DNA is not replicated between meiosis I and II. Together these are statements (ii) and (iv) in the linked item. Cohesin itself is not unique to meiosis II, and unchanged chromosome number alone does not distinguish meiosis II from mitosis.
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- ✓Homologues separate at anaphase I.
- ✓Crossing over occurs in prophase I.
- ✓Inherited variation must enter the germ line.
- ✓Can crossing over make sister chromatids non-identical before meiosis II?
- ✓Is there DNA replication between meiosis I and II?
Allele segregation does not depend on crossing over.
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