Birgid Schlindwein's
Hypermedia Glossary Of Genetic Terms
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Birgid Schlindwein'sHypermedia Glossary Of Genetic TermsSearch Results |
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| Meiosis | The term coined by Farmer and Moore (1905) for the process of two consecutive cell divisions in the diploid progenitors of sex cells. Meiosis results in four rather than two daughter cells (gametes), each with a haploid set of each chromosome pair. In meiosis I the prophase is more complex than that of mitosis. Five different stages can be differentiated: leptotene, zygotene, pachytene, diplotene and diakinesis. Prophase is followed by metaphase I, anaphase I, telophase I and interkinesis. Meiosis II could be described as a haploid mitosis resulting in four haploid gametes.
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| Diploid | A full set of genetic material, consisting of paired chromosomes one chromosome from each parental set. Most animal cells except the gamete have a diploid set of chromosomes. The diploid human genome has 46 chromosomes. Compare haploid and polyploid. |
| Gamete | Mature male or female reproductive cell (sperm or ovum) with a haploid set of chromosomes (23 for humans). |
| Haploid | A single set of chromosomes (half the full set of genetic material), present in the egg and sperm cells of animals and in the egg and pollen cells of plants (Gk. haploos, single). Human beings have 23 chromosomes in their reproductive cells. Compare diploid and polyploid. |
| Chromosome | The term was proposed by Waldeyer (1888) for the individual threads within a cell nucleus (gk. chroma, colour; soma, body). The self-replicating genetic structures of cells containing the cellular DNA that bears in its nucleotide sequence the linear array of genes. In prokaryotes, chromosomal DNA is circular, and the entire genome is carried on one chromosome. Eukaryotic genomes consist of a number of chromosomes whose DNA is associated with different kinds of proteins. |
| Prophase | Strasburger (1884) originally introduced this term for the early stage of nuclear division before (Gk. pro) the chromosomes divide into two chromatids, but from about 1905, with the realization that the chromosomes are double from the beginning of nuclear division, he used the term in the now universally adopted sense of the stage of mitosis or of meiosis I or II before breakdown of the nuclear membrane. condensation of chromosomes longitudinal splitting of chromosomes visible formation of spindle apparatus and fragmentation of nucleus membrane |
| Mitosis | The most frequent process of nuclear division (karyokinesis) in cells that produces daughter cells that are genetically identical to each other and to the parent cell. The mitosis is divided into four (or five) phases: prophase, prometaphase, metaphase, anaphase, telophase. Mitosis and interphase make the cell cylcle. |
| Leptotene | The term proposed by von Winiwarter (1900), originally as an adjective, to describe the nuclei at the earliest stage of prophase 1 of meiosis, when the chromosomes first become visible as fine threads and have not yet associated in pairs. (Gk. leptos, thin; taenia, ribbon.) |
| Zygotene | The term proposed by Gregoire (1907) to describe the nuclei at a particular stage of prophase 1 of meiosis when the homologous chromosomes are associating side by side. (Gk. zygon, yoke; taenia, ribbon.) |
| Pachytene | The term proposed by von Winiwarter (1900), originally as an adjective, to describe the nuclei at a particular stage of prophase 1 of meiosis when homologous chromosomes are associated throughout their length. (Gk. pachys, thick; taenia, ribon.) |
| Diplotene | The term proposed by von Winiwarter (1900), originally as an adjective, to describe the nuclei at a particular stage of prophase 1 of meiosis when the two chromosomes making up each homologous pair have separated from one another except at nodes (chiasmata) distributed along their length. The successive loops between the chiasmata all lie in one plane. (Gk. diploos, double; taenia, ribbon.) |
| Diakinesis | The term coined by Häcker (1897) for the stage of late prophase 1 of meiosis when the chromosomes are well separated from one another (Gk. kinesis, movement; dia, apart). This stage is recognized by the highly condensed condition of the chromosomes, the homologous pair of which are held together by chiasmata. In some organisms, just before or during diakinesis the chiasmata move to the ends of the chromosom arms (terminalization of chiasmata). When there are interstitia chiasmata, the successive loops into which the chromosome-pair is divided are set in planes at right angles to one another. |
| Metaphase | Strasburger (1884) originally introduced this term for the stage of nulear division after (Gk. meta) the chromosomes (ch) have divided into chromatids, but from about 1905, with the realization that the chromosomes are already double when nuclear division begins, he used the term in the now universally adopted sense of the stage in mitosis or meiosis I or II during which the chromosomes are aligned along the equatorial (metaphase) plate (ep) of the cell and kinetochores come into contact with the microtubuli of the spindle apparatus (s). Prometaphase Metaphase |
| Anaphase | Strasburger (1884) originally introduced this term for the stage of nuclear division when the contents of the nuclei were going back (Gk. ana) to their normal appearance, but from about 1905 he used the term in the now universally adopted sense of the stage of mitosis or of meiosis 1 or 2 when the daughter-chromosomes (or homologous chromosomes in meiosis 1) move towards opposite poles of the spindle. |
| Telophase | The last stage (Gk. telos, end) of mitosis, or of either division of meiosis, during which the chromosomes become progressively thinner and more elongated (Heidenhain, 1894). Telophase is said to begin with the formation of a nuclear membrane round each group of daughter-chromosomes.  Cell division |
| Interkinesis | The interphase between meiosis I and meiosis II. |
