chromatid

Information about chromatid

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Chromosome.
(1) Chromatid. One of the two identical parts of the chromosome after S phase.
(2) Centromere. The point where the two chromatids touch, and where the microtubules attach.
(3) Short arm
(4) Long arm.
A chromatid is one of two identical strands of DNA making up a chromosome that are joined at their centromeres, for the process of nuclear division (mitosis or meiosis). The term is used so long as the centromeres remain in contact. When they separate (during anaphase of mitosis and anaphase 2 of meiosis), the strands are called daughter-chromosomes.The tips of the chromatid are called telomeres.They are there to prevent the ends of the chromosome from attaching to other chromosomes. It has been said that after repeated cell replication, the telomeres gets shorter resulting in cell death. This means that the way telomeres work could determine the lifespan of a cell. However this has not been proven.[1]

In other words, a chromatid is "one-half of a replicated chromosome".[2] It should not be confused with the ploidity of an organism, which is the number of homologous versions of a chromosome.

Quantity

In humans, for example, there are normally 23 pairs of chromosomes in each cell. N=23. However, the quantity of chromatids is various. It can be either 4N, 2N or 1N. The latter is only seen in haploid gametes, with only one of each homologous chromosome pair. Such are created in gametogenesis.

4N

In a cell with 4N chromatids, there are 23 chromosome pairs (46 chromosomes), and each chromosome has 2 chromatids. Thus, there are 92 chromatids in each cell (4xN) which occurs during anaphase 2 of meiosis.

2N

Immediately after a mitosis, where a cell has divided in two, but not yet duplicated its DNA, there are still 23 chromosome pairs (46 chromosomes). However, each chromosome only has one chromatid. Thus there are 46 chromatids (2xN)

Alternatively, a haploid cell with two chromatids per chromosome also has 46 chromatids. However, this doesn't occur naturally in humans.

1N

Immediately after meiosis, each cell, called a gamete, only has half the amount of chromosomes (23 chromosomes). Furthermore, each chromosome only has one chromatid. Thus, there are 23 chromatids (1xN)

Etymology

The term chromatid was proposed by McClung (1900) for each of the four threads making up a chromosome-pair during meiosis. It was later used also for mitosis.

The term derives from the Greek chroma (colour); for the derivation of -id, see diploid.

References

1. ^ [1]
2. ^ [2]


Evolution of chromosomes
 •  • [ e]
Basic topics: Chromosome | Karyotype | Ploidy | Meiosis
Classification: Autosome | Sex chromosome
Evolution: Chromosomal inversion | Chromosomal translocation | Polyploidy
Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division.]] A chromosome is a single large macromolecule of DNA, and constitutes a physically organized form of DNA in a cell.
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centromere is a region of chromosomes with a special sequence and structure. The centromere plays a role in cellular division and the control of gene expression.

Function


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meiosis (IPA: /maɪˈəʊsɪs/) is the process by which one diploid eukaryotic cell divides to generate four haploid cells often called gametes.
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Anaphase, from the ancient Greek ανα (up) and φασις (stage), is the stage of mitosis when chromosomes separate in a eukaryotic cell.
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A telomere is a region of highly repetitive DNA at the end of a linear chromosome that functions as a disposable buffer. Every time linear chromosomes are replicated during late S phase, the DNA polymerase complex is incapable of replicating all the way to the end of the
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Ploidy is the number of homologous sets of chromosomes in a biological cell. The ploidy of cells can vary within an organism. In humans, most cells are diploid (containing one set of chromosomes from each parent), but sex cells (sperm and egg) are haploid.
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Gametogenesis is a process by which the diploid germ cells undergo a number of chromosomal and morphological changes to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of gametocytes into various gametes
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meiosis (IPA: /maɪˈəʊsɪs/) is the process by which one diploid eukaryotic cell divides to generate four haploid cells often called gametes.
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meiosis (IPA: /maɪˈəʊsɪs/) is the process by which one diploid eukaryotic cell divides to generate four haploid cells often called gametes.
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A gamete (from Ancient Greek γαμετης; translated gamete = wife, gametes = husband) is a cell that fuses with another gamete during fertilisation (conception) in organisms that reproduce sexually.
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Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division.]] A chromosome is a single large macromolecule of DNA, and constitutes a physically organized form of DNA in a cell.
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meiosis (IPA: /maɪˈəʊsɪs/) is the process by which one diploid eukaryotic cell divides to generate four haploid cells often called gametes.
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Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division.]] A chromosome is a single large macromolecule of DNA, and constitutes a physically organized form of DNA in a cell.
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karyotype is the observed characteristics (number, type, shape etc) of the chromosomes of an individual or species.

In normal diploid organisms, autosomal chromosomes are present in two identical copies, although polyploid cells have multiple copies of chromosomes and
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Ploidy is the number of homologous sets of chromosomes in a biological cell. The ploidy of cells can vary within an organism. In humans, most cells are diploid (containing one set of chromosomes from each parent), but sex cells (sperm and egg) are haploid.
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meiosis (IPA: /maɪˈəʊsɪs/) is the process by which one diploid eukaryotic cell divides to generate four haploid cells often called gametes.
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An autosome is a non-sex chromosome. It is an ordinarily pairedIn the case of higher ploidy levels than the usual diploid, there will be the same number of an autosome as the ploidy level itself. For example, in a pentaploid, there will be five copies of each autosome.
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A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most sexual organisms have two sexes. In many cases, sex determination is genetic: males and females have different alleles or even different genes that
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inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end. An inversion occurs when a single chromosome undergoes breakage and rearrangement within itself. Inversions are of two types: paracentric and pericentric.
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chromosome translocation is a chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes. It is detected on cytogenetics or a karyotype of affected cells.
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Polyploidy is the condition of some biological cells and organisms manifested by the presence of more than two homologous sets of chromosomes. Polyploid types are termed according to the number of chromosome sets in the nucleus: triploid (three sets; 3x),
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