cell theory
Meiosis was discovered and described for the first time in sea urchin eggs in 1876 by the German biologist Oscar Hertwig. It was described again in 1883, at the level of chromosomes, by the Belgian zoologist Edouard Van Beneden, in Ascaris worms' eggs. The significance of meiosis for reproduction and inheritance, however, was described only in 1890 by German biologist August Weismann, who noted that two cell divisions were necessary to transform one diploid cell into four haploid cells if the number of chromosomes had to be maintained. In 1911 the American geneticist Thomas Hunt Morgan observed crossover in Drosophila melanogaster meiosis and provided the first genetic evidence that genes are transmitted on chromosomes.
The term meiosis was introduced to biology by J.B. Farmer and J.E.S. Moore in 1905
Meiosis i/maɪˈoʊsɨs/ is a special type of cell division necessary for sexual reproduction which occurs or has occurred in all eukaryotes, including animals, plants and fungi, including both multi-celled and single-celled organisms.[1][2][3][4] The number of sets of chromosomes in the cell undergoing meiosis is reduced to half the original number, typically from two sets (diploid) to one set (haploid). The cells produced by meiosis are either gametes (the usual case in animals) or otherwise usually spores from which gametes are ultimately produced (the case in land plants). In many organisms, including all animals and land plants (but not some other groups such as fungi), gametes are called sperm in males and egg cells or ova in females. Since meiosis has halved the number of sets of chromosomes, when two gametes fuse during fertilisation, the number of sets of chromosomes in the resulting zygote is restored to the original number.
Meiotic division occurs in two stages, meiosis I and meiosis II, dividing the cells once at each stage. Before meiosis begins, during S phase of the cell cycle, the DNA of each chromosome is replicated, so that each chromosome has two
The term meiosis was introduced to biology by J.B. Farmer and J.E.S. Moore in 1905
Meiosis i/maɪˈoʊsɨs/ is a special type of cell division necessary for sexual reproduction which occurs or has occurred in all eukaryotes, including animals, plants and fungi, including both multi-celled and single-celled organisms.[1][2][3][4] The number of sets of chromosomes in the cell undergoing meiosis is reduced to half the original number, typically from two sets (diploid) to one set (haploid). The cells produced by meiosis are either gametes (the usual case in animals) or otherwise usually spores from which gametes are ultimately produced (the case in land plants). In many organisms, including all animals and land plants (but not some other groups such as fungi), gametes are called sperm in males and egg cells or ova in females. Since meiosis has halved the number of sets of chromosomes, when two gametes fuse during fertilisation, the number of sets of chromosomes in the resulting zygote is restored to the original number.
Meiotic division occurs in two stages, meiosis I and meiosis II, dividing the cells once at each stage. Before meiosis begins, during S phase of the cell cycle, the DNA of each chromosome is replicated, so that each chromosome has two