Skip to content. Skip to navigation. Actively dividing eukaryote cells pass through a series of stages known collectively as the cell cycle : two gap phases G1 and G2 ; an S for synthesis phase, in which the genetic material is duplicated; and an M phase, in which mitosis partitions the genetic material and the cell divides.
The critical steps for any sexually reproducing organism can be summarized in a few sentences. Sexual reproduction involves the combination of two sets of chromosomes via the fusing of two nuclei, each of which contains one set of chromosomes. Genes reside in those chromosomes.
Cell division as the base for life cycles and alternation of generation How can a meter-high corn plant arise from a seedling of just a few centimeters? How does it come that each child has iets own,individual properties? Not even an attempt will be made to explain the how and why of these true miracles here.
Sexual reproduction requires fertilizationthe union of two cells from two individual organisms. If those two cells each contain one set of chromosomes, then the resulting cell contains two sets of chromosomes. Haploid cells contain one set of chromosomes. Cells containing two sets of chromosomes are called diploid.
Meiosis is a special type of cell division process necessary for the sexual reproduction of all eukaryotes. The ever expanding meiosis research calls for an effective and specialized database that is not readily available yet. In the Resources part, a wealth of meiosis data collected by curation and manual review from published literatures and biological databases are integrated and organized into various sections, such as Cytology, Pathway, Species, Interactionand Expression.
Meiosis is a type of cell division in which number chromosome reduced to one half in the daughter cell. Sexual reproduction requires a genetic ontribution from two different sex cells. Egg and sperm cells are specialized sex ells.
Genetics owes a great debt to good drawing. Handmade graphic depictions of mitotic chromosomes by Walther Flemming Figure 1 and meiotic chromosomes by Walter Sutton provided an early record of the physical path of chromosomes during cell division. The physical movement of chromosomes could then be correlated with cells' patterns of genetic inheritance.
Russian Journal of Genetics. In the first meiotic division meiosis Ichiasmata are formed and rodlike bivalents orient equationally, and in anaphase I, sister chromatids segregate to the poles; the diploid chromosome number is maintained. Non-sister chromatids of homologous chromosomes remain in contact during interkinesis and prophase II and segregate in anaphase II, forming haploid chromosome sets. The segregation of sister chromatids in meiosis I was demonstrated by example of three plant species that were heterozygous for chromosomal rearrangements.
Sexual reproduction is a type of life cycle where generations alternate between cells with a single set of chromosomes haploid and cells with a double set of chromosomes diploid. Diploid cells divide into haploid cells in a process called meiosis. Two haploid cells combine into one diploid cell in a process called fertilisation.
Recent investigations on Biology Education in Brazil showed that most classes involve the use of textbooks and illustrations [ 12 ]. Theoretical and lecture classes predominate in Sciences and Biology courses [ 34 ], and there is a scarce variety of teaching materials. On the other hand, recent investigations have led to the development of several practical lessons to improve education quality. Some studies involve proposals of biological models [ 5 ]; elaboration of teaching games [ 6 ]; analysis of biological specimens [ 7 ]; laboratory lessons using microscopy [ 8 ]; ecotourism in natural ecosystems, observation of wildlife and environment [ 9 ] and visits to Natural History Museums, Zoo and Botanical Gardens [ 3 ].