The chromosomes in the nucleus change from being loosely dispersed to becoming more condensed. It is difficult to pick out an individual chromosome because they are each so spread out. Image by Marjorie Hanneman.ĭuring interphase, the chromosomes look like a plate of spaghetti in the nucleus. Prophase is the beginning of mitosis (Figure 3). We will describe the events at each stage that are important in understanding the distribution of genes during cell division. These pictures depict the four stages of mitosis. Therefore, we will include genes on our chromosome diagrams and slide show. Chromosomes are important because they contain genes. Mitosis is an organized procession of activity in the cell that allows the replicated chromosomes to be properly divided into two identical cells. Remember, replication takes place during interphase when the chromosomes are dispersed structures in the nucleus. Obviously, replicating the chromosomes is a prerequisite to mitosis. In the cells of our body, we start with 46 chromosomes in a single cell and end up with 46 chromosomes in two cells. The objective of mitosis is to make two genetically identical cells from a single cell. Figure 2. Multicellular organisms that sexually reproduce have diploid and haploid cells. Image by Marjorie Hanneman. Mitosis and meiosis are the two types of cell division. Since you started as a single cell with 46 chromosomes, there must be two types of cell division taking place in your body to accommodate both somatic and gamete cells. You have cells with 46 chromosomes ( somatic or body cells) and cells with 23 chromosomes ( gamete or sex cells). Rounds of the cell cycle continued over and over to form the body you have today. As long as you live, some of your cells must be able to complete the cell cycle.įrom a cytogenetics point of view, you have two types of cells in your body. This completes the life cycle of the zygote and starts the lifecycle of the new cells. Therefore, it goes through mitosis and gives rise to two daughter cells. For the zygote, the goal is to make more somatic cells. ’M’ could be mitosis or meiosis depending on the type of cell. The G1, S and G2 phases together are called interphase. The third part of the cell cycle is the G2 phase where the cell prepares for division. Here, the cell replicates its chromosomes so that it has a copy of each chromosome to pass on to daughter cells. The second part of the cell cycle is the S phase (synthesis phase). However, a zygote does not grow in size, but instead continues the cell cycle so it can quickly give rise to more cells. Some cells differentiate into specialized cells and then never leave this phase. Cells can go through growth and development in this phase. The first part of the cell cycle is the G1 phase. The cell cycle depicts the stages in the life of a cell. The main idea is that when new cells are made from existing cells, the new cells start their lifecycle, and the old cells end theirs. We depict the cell cycle in a circular diagram although the cells in your body do not actually go around in circles. The cell cycle is the life cycle of a single cell. You have come a long way since then, progressing one cell cycle at a time. Your age plus about nine months ago you were a zygote, a single cell formed when the sperm and egg from your biological parents fused in a fallopian tube (or possibly in a test tube if in vitro fertilization factored into your birth). Let us think about the cell cycle from a personal point of view. Understanding multicellular organisms requires an understanding of the lifecycle of the cells that make up the organism. This single cell established the life of the organism. Furthermore, the millions of cells that makeup a mature organism originated from a single cell formed when the male and female gametes from the parents of the organism fused. Even though they have diverse functions, each somatic cell in the organism normally has the same chromosomes and therefore the same genetic makeup. The cells that make up different tissues have different shapes and perform different functions for the plant or animal. Multicellular organisms such as plants and animals are composed of millions to trillions (1,000,000,000) of cells that work together. Describe the role of meiosis in gamete formation and how it relates to inheritance.Track chromosome and chromatid number through all stages of meiosis.Explain the events of all stages of meiosis.
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