There are two types of cell division: mitosis and meiosis. Meiosis is the type of cell division that creates egg and sperm cells. Mitosis is a fundamental process for life. During mitosis, a cell duplicates all of its contents, including its chromosomes, and splits to form two identical daughter cells. Because this process is so critical, the steps of mitosis are carefully controlled by certain genes. When mitosis is not regulated correctly, health problems such as cancer can result.
The separated chromosomes are then pulled by the spindle to opposite poles of the cell. Anaphase ensures that each daughter cell receives an identical set of chromosomes.
Finally, during telophase, a nuclear membrane forms around each set of chromosomes to separate the nuclear DNA from the cytoplasm. The chromosomes begin to uncoil, which makes them diffuse and less compact. Along with telophase, the cell undergoes a separate process called cytokinesis that divides the cytoplasm of the parental cell into two daughter cells. Further Exploration Concept Links for further exploration chromatin chromosome prophase diploid prometaphase spindle fibers replication eukaryote cytoplasm nucleus mitosis metaphase cytokinesis meiosis anaphase telophase.
The end result of meiosis is four haploid daughter cells that each contain different genetic information from each other and the parent cell. Click for more detail. Meiosis I halves the number of chromosomes and is also when crossing over happens. Meiosis II halves the amount of genetic information in each chromosome of each cell. The end result is four daughter cells called haploid cells.
Haploid cells only have one set of chromosomes - half the number of chromosomes as the parent cell. Before meiosis I starts, the cell goes through interphase. Just like in mitosis, the parent cell uses this time to prepare for cell division by gathering nutrients and energy and making a copy of its DNA. During the next stages of meiosis, this DNA will be switched around during genetic recombination and then divided between four haploid cells.
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How Do We Sense Taste? How Do We Sense Touch? What is Evolutionary Medicine? What's a Biologist? What's a GMO? One way of thinking about ploidy is the number of possible alleles for each gene a cell can have. Right after meiosis I, the homologous chromosomes have separated into different cells. Each homolog carries one copy of the gene, and each gene could be a different allele, but these two homologs are now in two different cells. Though it looks like there are two of each chromosome in each cell, these are duplicated chromosomes; ie, it is one chromosome which has been copied, so there is only one possible allele in the cell just two copies of it.
The second meiotic division is where sister duplicated chromatids separate. It resembles mitosis of a haploid cell. At the start of the second division, each cell contains 1N chromosomes, each consisting of a pair of sister chromatids joined at the centromere.
Here is a simplified diagram illustrating the overall process and products of meiosis:. Meiosis Overview from Wikipedia by Rdbickel. And here is a video that walks through the steps of meiosis: It is very important that you recognize how and why cells become haploid after meiosis I. To confirm for yourself that you understand meiosis, work through one or more of these interactive tutorials:. Chromosomes by definition contain the DNA that makes up the fundamental genome of the cell.
In a prokaryote, the genome is usually packaged into one circular chromosome consisting of a circular DNA molecule of a few million base pairs Mbp. In eukaryotes, the genome is packaged into multiple linear chromosomes, each consisting of a linear DNA molecule of tens or hundreds of Mbp.
Chromosomes exist at all different phases of the cell cycle. The chromosome number, N, in eukaryotes, refers to the number of chromosomes in a haploid cell, or gamete sperm or egg cell. Diploid cells all the cells in our body except our gametes have 2N chromosomes, because a diploid organism is created by union of 2 gametes each containing 1N chromosomes.
A pair of sister chromatids is one chromosome because it has genetic information alleles inherited from only one parent. A pair of homologous chromosomes, each consisting of a single chromatid in a daughter cell at the end of mitosis, has alleles from the father and from the mother, and counts as 2 chromosomes.
This chromosome number stays the same after chromosome replication during S phase: each chromosome entering cell division now consists of a pair of sister chromatids joined together at the centromere.
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