Nuclear division is aprocess where a parent cell is divided into two or more daughter cells.
Thereare two types of cell division processes in multicellular organisms. The firstone is mitosis which is an asexual process. This is due to the parent cell dividinginto two daughter cells which contain the same number of chromosomes as theparent cell (Lodish et al.
, 2003).These cells are called as diploid cells as they contain the full set ofchromosomes (Lodish et al., 2003). Meiosis is a sexualprocess where four daughter cells are produced with half the number ofchromosomes. This type of cell is known as a haploid cell (Alberts et al., 2009). Genetic variation inmulticellular organisms takes place in the process of meiosis and not inmitosis. In meiosis genetic variation is accomplished by two procedures-crossing over and independent assortment (Weaver, 2012).
The process of crossingover takes place in the prophase I stage. Crossing over is the exchange ofgenetic material between two homologous chromosomes (Weaver, 2012). A sectionof the non-sister chromatids of the two homologous chromosomes crosses overeach other. The crossed over section is called a chiasma. At this point, the cohesionproteins hold the sister chromatids along their entire length (Alberts et al.
, 2009). Many chiasmata can bepresent indicating that many crossovers take place (Alberts et al., 2009). The crossing over processis also important for proper segregation of the homologous pair (Alberts et al.
, 2009). The chiasma pulls thesister chromatids in opposite direction of the spindle fiber contraction andthe cohesion proteins unbind allowing the homologous pair with newly formedchromatid to separate (Alberts et al.,2009). Crossing overplays a major role in genetic variation as it increases thediversity of phenotypes formed. The second process toincrease genetic variation is carried out according to the law of independentassortment which was developed by Gregor Mendel.
This process is carried duringthe metaphase I stage. According to the law, the alleles for the traits areseparated when the gametes are formed. These separated alleles then once againrecombine randomly during fertilization presenting various combinations ofgenotypes (Bailey, 2017). The random recombination is valuable as somemutations that could take place would be canceled out allowing the offspring tohave a better survival chance than the parents (Weaver, 2012). Mendel arrivedat this conclusion by carrying out a cross-pollination experiment for differentcolored pea plants (Bailey, 2017).
The crossing over,independent assortment processes including mutation contribute greatly for thegenetic variation of multicellular organisms.