Meiosis I and meiosis II together generate genetic variation by shuffling and reshaping chromosomes so that each gamete ends up with a unique combination of alleles.

Big idea

  • In meiosis I , homologous chromosomes pair, swap segments, and then separate, mixing parental genes into new combinations.
  • In meiosis II , the sister chromatids of each chromosome separate so that each gamete receives just one chromatid from every chromosome pair, “freezing in” those new combinations and distributing them differently to each gamete.

What meiosis I does (using the diagram)

Most textbook diagrams show these key features in meiosis I:

  1. Prophase I – crossing over
    • Homologous chromosomes (one from each parent) pair up side by side, often drawn as X‑shaped “bivalents.”
 * At points called chiasmata, non‑sister chromatids break and rejoin, exchanging corresponding segments of DNA.
 * After crossing over, each chromatid is a new **recombinant** mix of maternal and paternal alleles, which the diagram usually shows by changing colours or patterns along the chromatids.
  1. Metaphase I – independent assortment
    • Homologous pairs line up in the middle of the cell as bivalents, but the way each pair “faces” (which side the maternal vs paternal chromosome is on) is random.
 * The diagram often shows several pairs with different orientations, like some maternal chromosomes pointing to one pole and some to the other.
 * When the pairs separate in anaphase I, each new cell gets a random mix of maternal and paternal chromosomes, creating many possible combinations of whole chromosomes.

Together, crossing over and independent assortment in meiosis I massively shuffle alleles, turning the original set of chromosomes into new mixtures that didn’t exist in either parent.

What meiosis II adds

In diagrams, meiosis II looks similar to mitosis:

  • Each cell from meiosis I contains chromosomes that already carry new combinations of alleles because of crossing over and assortment.
  • In metaphase II, chromosomes line up singly; in anaphase II, sister chromatids separate and are pulled to opposite poles.
  • Because crossing over made sister chromatids non‑identical, separating them creates four gametes that all have different chromatids and therefore different allele combinations, often shown as four cells with different colour patterns in the diagram.

So meiosis II does not create new combinations by itself in the same dramatic way as meiosis I, but it distributes the recombinant chromatids into separate gametes, ensuring that each gamete is genetically distinct.

Putting it together (how the diagram answers the question)

If you relate your diagram to this explanation, you can say something like:

  • The diagram shows homologous chromosomes pairing and crossing over in prophase I, which swaps segments between non‑sister chromatids and produces recombinant chromosomes with new allele combinations.
  • It then shows homologous pairs lining up randomly at the equator in metaphase I, so each daughter cell receives a different random combination of maternal and paternal chromosomes after anaphase I.
  • In meiosis II, the diagram shows the separation of non‑identical sister chromatids into four haploid cells, each with a unique set of recombinant chromatids.

Together, these steps explain how meiosis I and meiosis II contribute to genetic variation : meiosis I creates new allele combinations through crossing over and independent assortment, and meiosis II separates and packages those different chromatids into four genetically different gametes.