The meiotic cohesin subunit Rec8 in the pathogenic fungus Cryptococcus neoformans

Abstract

The term ‘meiosis’ originates from the Ancient Greek word meíōsis, which means “a lessening”. This is apt, given that the process of meiosis is a special mode of cell division wherein chromosome number or ploidy is halved, creating haploid cells from a diploid cell(Ohkura 2015). It is essential for sexual reproduction, which, in turn, is the most common means of generating genetic diversity. This genetic diversity increases the likelihood of survival of at least some individuals of a population in the event of a calamity and reduces the incidences of unfavourable genetic traits on the whole. Meiosis can be considered one of the first and most important “innovations” of the eukaryotes. Indeed, it has been theorized that linear chromosomes that are seen in eukaryotes may have arisen because of the advent of meiosis (Goodenough and Heitman 2014). Sexual reproduction is comprised of two broad steps: conjugation, or fertilisation; and the meiotic cell division itself. During the former, two genetically distinct cells fuse, nuclear fusion or karyogamy may or may not happen simultaneously, and the outcome of this is a diploid cell. In diploid organisms, fertilization occurs to restore a diploid state during or after meiosis required for gamete formation, but haploid organisms undergo the conjugation step prior to meiotic division. The concept of meiosis was first discovered by the German biologist Oscar Hertwig in 1876, when he observed the fusion of egg and sperm in the transparent Sea Urchin Egg, and concluded that the nuclei of the two cells contributed to the inherited traits passed on to the offspring. It was described eight years later at the level of chromosomes in the eggs of the roundworm Ascaris,by the Belgian zoologist Edouard Van Beneden(Hamoir 1992). However, its significance for genetic inheritance was only understood in 1890 by the German scientist August Weismann, who observed that two cell divisions were imperative for the transformation of one diploid cell into four haploid cells,which, in turn, was needed to maintain the number of chromosomes or the ploidy.