subject: Mutations and Meiosis [print this page] Mutations and Meiosis Mutations and Meiosis
Mutations within our genome occurs all the time, especially in our modern age due to enormous amount of ionising radiation (e.g. X rays, Gamma rays) emitted from the Sun or from the electronic goods used in the house; causing inversions, translocations and deletions in our genome. Adding to the problem are Alkylating chemicals (e.g. EMS) and Transposons which cause point-mutations and insertions respectively. Most mutations however, are corrected by the DNA-repair mechanisms also present within the genome, which is the reason why we can carry on living for quite a long time.
These changes in the genome can activate oncogenes by deleting tumour suppressor genes, causing cancer; inactivate a certain gene which leads to malfunction in the processes the respective gene plays a part in. The main problem arises when these mutations occur within the Germline, since they will be passed onto the next generation or more usually, cause infertility/semi-infertility. Mutations occurring in somatic cells will only affect the individual who inherits them.
Focusing on reciprocal translocations, which is the exchange of some fraction of the end of one chromosome with a part of another chromosome. Since there are two copies of each chromosome in humans (excluding sex chromosomes), reciprocal translocations cause homology between - under normal circumstances, non-homologous chromosomes. This causes problems during meiosis when homologous chromosomes line up at metaphase because of the fact that now there exists four chromosomes which have homology. This causes quadrivalents to form at the metaphase plate. During anaphase when the chromosomes are being pulled to the opposite sides of the cell, there exists several ways of separating them. Adjacently pulling the chromosomes would lead to duplication and deletions being present in the gamete which usually are unviable. Alternate separation however, results in viable ones. This is the reason why individuals with translocations are generally semi-fertile (See Quadrivalents).
Moving on to inversions, which results in change of gene order and/or DNA sequences; again causing problems during meiosis with the formation of inversion loops. Crossovers can occur within the loop and when the chromosomes are being pulled during anaphase; this results in the formation of dicentric chromosomes and an acentric fragment which is lost and degraded. The acentric fragment is likely to have genes within it and it is as likely to cause harm to the individual (See Dicentric Chromosome).
As one can see mutations are always occurring and there is not much to do to prevent it. What can be prevented are some late onset diseases when they can be detected early, using Comparative Genome Hybridisation and/or Karyotyping (by Flouresence In Situ Hybridisation). The most important thing above all is to inform the public about the harm of radiation emitted from the electronic goods we use in our houses, thus decreasing mutations and the above mentioned problems caused by mutations; saving a lot of money (spent on treatments) and people.
