DNA Replication before Meiosis
- Before meiosis occurs, all of the DNA inside the nucleus of the 'parent' cell is replicated
- This occurs during a period of the cell cycle known as interphase
- Once this has occurred, each chromosome now consists of two genetically identical sister chromatids, which are joined together by a centromere
- The sister chromatids are genetically identical because DNA replication is a very accurate process and only a very small number of mistakes occur when DNA is being copied
- The two DNA molecules formed by DNA replication prior to meiosis are considered to be sister chromatids until the splitting of the centromere at the start of anaphase (a stage during meiosis II, during which the sister chromatids are pulled apart)
- After this, they are once again considered as individual chromosomes
DNA replication before meiosis
Exam Tip
Understanding the difference between chromosomes and chromatids can be difficult. We count chromosomes by the number of centromeres present. So when the 46 chromosomes duplicate during interphase and the amount of DNA in the cell doubles there are still only 46 chromosomes present because there are still only 46 centromeres present. However, there are now 92 chromatids, which are strands of replicated chromosomes.