# Crossing over and independent assortment Two sources of variation in meiosis. In crossing over, homologous chromosomes swap pieces in prophase I. In independent assortment, each pair lines up and separates at random. Biology (university) · Part 06: Cell cycle, mitosis and meiosis · Card 7 of 8 · Last updated 2026-10-19 ## Analogy Shuffling and then cutting a deck of cards. ## Example **Combinations** 23 chromosome pairs. 2^23 = 8,388,608. Crossing over adds many more. ## In practice With 23 pairs, independent assortment alone gives 2 to the power of 23, over 8 million, different combinations. ## Practice ### Flashcards - **When does crossing over occur?** In prophase I of meiosis. ### Interview questions **Describe the ways meiosis produces genetic variation.** - Crossing over in prophase I - Independent assortment of homologous pairs - Random fertilisation adds more variation ## Questions people ask ### What is a chiasma? A chiasma is the place where two homologous chromosomes are joined while crossing over. Under the microscope it appears as an X-shaped link. It shows where pieces have been swapped, and it helps hold the pair together so that they separate correctly in anaphase I. ### Why is genetic variation useful? Variation means individuals in a population differ, so when conditions change, such as a new disease, some are likely to survive. Without variation, a single threat could wipe out everyone. Meiosis and sexual reproduction constantly shuffle alleles, giving natural selection more to work with. ## Related concepts - [Meiosis](https://studyvisually.com/learn/science/biology-university/biology-university-part-6/biology-university-part-6-concept-6) - [Nondisjunction](https://studyvisually.com/learn/science/biology-university/biology-university-part-6/biology-university-part-6-concept-8) Web page: https://studyvisually.com/learn/science/biology-university/biology-university-part-6/biology-university-part-6-concept-7 Study this card in the app: https://studyvisually.com/app/learn?category=biology-university&card=biology-university-part-6-concept-7