Crossing-over between homologous chromosomes

In the picture

1. 1The chiasma: where two non-sister chromatids cross and swap segments
2. 2An unchanged chromatid: it keeps the original combination of alleles
3. 3A blue chromatid with a red tip: a new, recombinant combination of alleles
4. 4A red chromatid with a blue tip: the matching recombinant from the swap

Examples

• Brothers and sisters have the same parents but each inherits a different mix of traits.
• Two friends swap the second halves of their playlists: each ends up with a new mix, and no song is lost.

Quiz: Crossing-over between homologous chromosomes (Age 18)

1. 1

   At which stage does crossing-over take place?

   • Prophase of mitosis
   • Anaphase II of meiosis
   • Prophase I of meiosis
2. 2

   What is a chiasma?

   • The point where two non-sister chromatids cross and swap segments
   • The point where homologous chromosomes separate at the end of meiosis
   • The point where two sister chromatids are held together
3. 3

   How does crossing-over affect the gametes that form?

   • It gives them new combinations of existing alleles, increasing genetic variation
   • It makes every chromatid keep its original combination of alleles
   • It creates brand-new alleles that did not exist on either parent chromosome

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.