BRAINCAKEThe Importance of Meiosis
Meiosis matters for two main reasons: it keeps the chromosome number constant from one generation to the next, and it produces genetic variation.
1. Keeping the chromosome number constant. Meiosis halves the chromosome number, producing haploid gametes. At fertilisation two haploid gametes fuse, restoring the diploid number. Without meiosis, the chromosome number would double every generation: human gametes would have 46 chromosomes, zygotes 92, and the next generation's zygotes 184.
2. Producing genetic variation. Meiosis makes gametes that are genetically different from each other in two ways:
• Crossing over in prophase I exchanges sections between non-sister chromatids of homologous chromosomes, producing new combinations of alleles on each chromosome.
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Key terms in this lesson
- crossing over
- The exchange of sections of DNA between non-sister chromatids of homologous chromosomes during meiosis, producing new combinations of alleles.
- independent assortment
- The random separation of homologous chromosome pairs into gametes during meiosis, producing different combinations of maternal and paternal chromosomes.
More in Meiosis and Sexual Reproduction
- Metaphase 1
- Anaphase 1
- Telophase 1
- Meiosis 2
- Chromosome Mutation
- Non-disjunction
- Down's Syndrome
- Turner's Syndrome
All 28 lessons in Meiosis and Sexual Reproduction · All Edexcel AS-level Biology topics