Meiosis
Two divisions that turn one diploid cell into four haploid cells, each with half the chromosomes. It makes gametes (eggs and sperm). Meiosis I separates homologous pairs. Meiosis II separates sister chromatids.
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Analogy
Dealing a deck of 46 cards into four hands of 23.
Example
Body cell: 46 (diploid).After meiosis I: 23 each.After meiosis II: 4 cells,23 each.
In practice
A human body cell has 46 chromosomes. An egg or sperm has 23.
Practice
Flashcards
- How many cells and what chromosome number result from meiosis?Four haploid cells, each with half the chromosomes.
- What does meiosis I separate?Homologous chromosome pairs.
Interview questions
- Compare mitosis and meiosis in terms of purpose, number of divisions, daughter cells and genetic variation.
- Mitosis for growth and repair, meiosis for gametes
- Mitosis one division, meiosis two
- Mitosis two identical diploid cells
- Meiosis four haploid cells, varied
- 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
Why does meiosis need to halve the chromosome number?
Fertilisation joins two gametes. If each had 46 chromosomes, the baby would have 92, and the number would double every generation. Halving the number in gametes means the fertilised egg returns to the normal diploid number of 46, and the species keeps a steady chromosome count generation after generation.
What are homologous chromosomes?
A homologous pair consists of two chromosomes of the same size and gene order, one from each parent. They carry the same genes but may have different versions (alleles). Humans have 23 pairs. In meiosis I the two members of each pair pair up and then separate.