Hypermedia Glossary Of Genetic Terms
|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.)|
|Nucleus||The term introduced by Brown (1833) for the more or less spherical structure which occures in cells and stains deeply with basic dyes. The cellular organelle in eukaryotes that contains the genetic material.|
|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
|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.
|Homologous chromosome||A pair of chromosomes containing the same linear gene sequences, each derived from one parent. Humans normally have 22 pairs of homologous chromosomes and 2 X chromosomes (female) or 1 X and 1 Y chromosome (male). Compare sex chromosomes.|
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