Let’s try to tie all of this information together and see how it applies to chromosome and chromatid count during the various stages of cell replication.įirst, during the S phase of interphase, the genetic material of a cell is duplicated. At the beginning of mitosis, for example, a chromosome consists of two sister chromatids – chromatids are the term used to describe the chromosome in its duplicated state. Chromosomes can exist in duplicated or unduplicated states. Chromosomes are an even denser packaging of chromatin that are visible with a light microscope, particularly during metaphase. In prophase I, the two different versions of each chromosome (homologues) find each other and connect so they can line up parallel to each other on the metaphase plate and ultimately be separated to form two daughter cells. However, during mitosis and meiosis, chromatin exists in an additional level of organization known as a chromosome. When meiosis starts, each cell contains two copies of each chromosomeone from each parent.
This time there are not homologous chromosomes to be paired with. 3.2 Meiosis II 4 Origin and function Toggle Origin and function subsection 4.1 Prophase I arrest 5 Occurrence Toggle Occurrence subsection 5.1 In life cycles 5.2 In plants and animals 5.3 In mammals 5.4 Flagellates 6 Role in human genetics and disease Toggle Role in human genetics and disease subsection 6. Throughout most of the cell cycle, DNA is packaged in the form of chromatin. are aligned at the center of the cell (Fig. To first clarify this topic, it is first essential to understand some basic definitions.Ĭhromatin is the general packaging of DNA around histone proteins – this arrangement of DNA helps to condense DNA to fit within the nucleus of the cell. Meiosis has two stages: meiosis I and meiosis II. A topic in biology that many students find challenging is the number of chromosomes and chromatids present during the various stages of meiosis and mitosis in eukaryotes. Meiosis is a process that creates sex cells (gametes) with half the number of chromosomes of the parent cell.
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