Meiosis

Abstract

Meiosis is a specialised type of cell division, the principal function of which is to produce spores/gametes (sperm and eggs in mammals) that have the haploid number of chromosomes. In humans, this represents a reduction from 46 (23 pairs) to 23 chromosomes (one complete set) in sperm and eggs. The normal somatic number of 46 chromosomes is restored at fertilisation. The most complex part of meiosis (prophase I) involves intimate pairing and synapsis of the homologous chromosomes followed by reciprocal recombination/crossing‐over/chiasma formation. In most organisms, chiasma formation is obligatory to allow the regular segregation of the (rearranged) homologues at the first (reductional) division (anaphase I). In mammals, there are substantial differences between the two sexes as regards the meiotic process. Mammalian female prophase I takes place during foetal development, and the second meiotic cell division is not completed until after fertilisation. In sharp contrast, mammalian male meiosis does not start until puberty and is continuous throughout life. Key Concepts: Meiosis is the term used for the cell divisions leading to gametes, sperm and eggs in mammals. At meiosis, the chromosome number is halved compared to that in somatic cell nuclei. Meiosis takes place in the germ line, testes and ovaries in mammals. The meiotic process is very different in the two mammalian sexes. Female mammalian meiosis is subdivided into three stages: the first taking place during foetal development, the second just before ovulation and the third after fertilisation. Male mammalian meiosis starts at puberty and is ongoing throughout life. Reciprocal recombination/crossing‐over/chiasma formation (taking place during foetal development in mammalian females) is necessary for normal first meiotic cell division (taking place just before ovulation in mammalian females). Many of the proteins involved in the meiotic recombination process, as well as some structural components of meiotic chromosomes, are conserved from yeast to man. Human females produce only 300–400 mature eggs in a lifetime, in stark contrast to human males who normally produce around 300–400 million sperm daily. An abnormal chromosome number (aneuploidy) is common in humans and is thought to arise due to abnormalities in meiotic cell divisions.

Inferring the Brassica rapa Interactome Using Protein–Protein Interaction Data from Arabidopsis thaliana

“…During meiosis, a single round of DNA replication is followed by two rounds of nuclear division to produce four haploid gametes. Many genes/proteins participate in meiosis, for example, see reviews (Ma, 2006; Hultén, 2010; Osman et al, 2011). Here we used the list of 71 meiotic genes presented in (Yang et al, 2010), with the addition of AtASY3 (At2g46980), recently described by the Birmingham meiosis group (Ferdous et al, 2012).…”

On the origin of crossover interference: A chromosome oscillatory movement (COM) model

“…the non-random placement of crossovers along the length of individual chromosomes with a reduced probability of occurrence of one crossover in the vicinity of another, is a universal feature in the outstanding majority of eukaryotic organisms. The patterns of crossovers/chiasmata on individual chromosome pairs, as governed by interference, are of crucial importance for regular segregation of the homologous parental chromosomes at the meiosis I division [review in [ 1 - 3 ]] as schematically illustrated in Figure 1a .…”

“…(b) Progression through Metaphase I to Anaphase I leading to the halving of the chromosome number, Metaphase II and Anaphase II where the chromatids separate (similar to mitotic Anaphase) and Telophase II comprising the four haploid daughter cell nuclei. Reproduced from [ 3. ]…”