Errors that can occur during Meiosis
Meiosis results in the reduction of chromosome numbers by half during cell division and this is essential in reproduction to ensure constant chromosome numbers in the offspring. However, its indispensable role in reproduction poses a great risk because any alteration in the genetic makeup of the parents is transmitted to the filial generations. This paper is purposely documented to discuss the errors that can occur during meiosis and provide the corresponding genetic changes and disorders.
The first stage of meiosis that involves DNA replication is prone to copying errors. The DNA replication errors result into disruption of gene sequences and the ultimate consequence is mutation of the genetic components. Mutations alter the final protein structures and hence, their functions also changes. Therefore, the mutations can lead to harmful effects or latent outcomes. An example of a DNA replication stage error disorder is the sickle-cell anemia. Hoban, Cost, Mendel, Romero, Kaufman, Joglekar, Ho, Lumaquin, Gray, Lill, and Cooper (2015) opine that the essential feature of sickle-cell disease is a single point gene mutation in the codon number seven of the β-globin gene sequence (p. 2597). The point mutation results in different protein structures that alter the functional components of hemoglobin. According to Voskaridou (2014), the point gene mutation results in the substitution of the glutamic acid residue with a valine residue in the β-globin chain that leads to the formation of the sickle Hemoglobin, HbS (p. 60). This assertion depicts that the initial alteration in genetic sequence during DNA replication can lead to sickle cell disease due to amino acid substitution. The associated symptoms for sickle-cell anemia include acute renal failure, ophthalmologic complications, and fever-infections.
Genetic errors can also during the recombination phase of meiosis. Homologous chromosomes exchange their genetic materials during the recombination phase. Baudat, Imai, and de Massy (2013) posit that the exchange of the genetic materials between homologous chromosomes during recombination contributes to the transmission transformed combinations of the linked alleles (p. 794). The homologous chromosomes align and pair exactly before, breaking, exchanging DNA portions, and rejoining. However, it is evident that there are errors that might result during the exchange of the genetic materials. Homologous chromosomes can misalign and the result would be one daughter cell have an extra chromosome while the other daughter cell would miss a chromosome leading to loss of some genetic material. The daughter cell with extra chromosome will have an over-expression of the genes located within the extra chromosome. Absence of meiotic recombination is as well an error of clinical significance. According to Tempest (2011), it is significance to apprehend achiasmate bivalents because lack of recombination foci result to sperm aneuploidy and consequent male infertility (p. 95). The sperm aneuploidy results to male infertility because there is mitigation of sperm production following the destruction of the abnormal sperms.
There is also a risk during meiotic recombination of pairing of non-homologous chromosomes that may lead to chromosomal translocation. Roukos and Misteli (2014) define chromosome translocation as the genome abnormality whereby a chromosomal segment breaks and either its portion or the whole of it integrates to a different chromosome (p. 293). Translocation reshapes gene sequence and in some cases, when the regulatory portions of DNA are involved, there occur misregulation of the genes. Consequently, there are several diseases associated with disproportionate gene segments or disturbed regulatory portions. Unregulated cell division due to chromosome translocations involving regulatory segments of DNA is likely to cause cancers. Cancer is basically the uncontrolled proliferation of cells. Roukos and Misteli (2014) also assert that chromosome translocations are remarkably associated with several human cancers, schizophrenia, and infertility (p. 293). The basis behind the disorders associated with the chromosome translocation is the creation of gene dosage imbalances after the chromosome translocations. Additionally, deletion of a portion of the chromosomes is an error that can also lead to permanent genetic change. Uzunhan, Sayinbatur, Caliskan, Sahin, and Aydin (2014) assert that a partial deletion, either interstitial or terminal, of the shorter arm of chromosome number 5 causes cri-du-chat (p. 209). Therefore, genetic deletion is of clinical significance as well.
The last stage where meiotic errors can occur is the chromosomal segregation step. The homologous chromosomes should segregate into gametes in such a way that all the gametes should have equal number of chromosomes that is half the original number in the parental cell. Under normal circumstances, the four chromatids of a meiotic tetrad will segregate completely with each of the four daughter cells receiving one chromatid. However, there could be errors that limit the separation of some homologous chromosomes. Consequently, some daughter cells will have more chromosomes than others after a failure of the homologous chromosomes to segregate. This chromosomal imbalance is the basis for clinical conditions such as trisomy. One of the effects of chromosomal trisomy is the Down’s syndrome. According to Li, Chang, Wang, Hirata, Papayannopoulou, and Russell (2012), Down syndrome results due to an extra copy of chromosome number 21 and has several clinical manifestations such as premature aging, heart defects, leukemia, and impaired cognition (p. 615). The resultant effects of the Down syndrome are manifested because of the extra chromosomal copies and the corresponding regulatory sequences. An individual with the Down syndrome disorder received an extra copy of chromosome number 21 from a parent. The basic argument is to demystify the influence of gene dosage on the phenotypic expression. Epstein and Holtzman (2013) argue that the higher the dosage for a particular gene, the greater the synthesis and the concentration of the ultimate gene product (p. 106). Therefore, the individuals with the trisomy for chromosome 21 will have increased expression of the genes coded in the chromosome 21.
The alternative consequence of inappropriate segregation is the inadequate number of chromosomes within the daughter cells after meiotic cell divisions. As one daughter cell receives an extra chromosome that did not segregate, the corresponding daughter cell will suffer from a deficit in chromosome number by the number of the extra chromosomes received by the counterpart. A specific example of such a disorder is the Turner syndrome. Hook and Warburton (2014) posit that the karyotype for Turner syndrome is 45; X and most embryos with the syndrome do not survive the gestational duration (p. 417). The 45; X karyotype confirms that the number of chromosomes in Turner syndrome are less than 46. The inadequacy of the chromosome number is due to the pair that did not segregate that moved to the corresponding daughter cell.
Another nondisjunction disorder is the Klinefelter syndrome. According to Groth, Skakkebæk, Høst, Gravholt, and Bojesen (2012), Klinefelter syndrome results in male due to an extra X chromosome and the associated symptoms include hypergonadotropic hypogonadism, small testis, and cognitive impairment (p. 20). The symptoms of hypogonadism are experienced because there would be an over-expression of the female characteristics due to an extra X chromosome.
In conclusion, the process of meiosis is not always perfect in the production of the daughter cell. Meiosis is prone to errors such as translocation, deletion, non-disjunction, and lack of recombination. These errors result in disorders that severe the lives of the victims. A vivid example is the change in genetic sequence that leads to the change in the β-globin change and thus, causing sickle-cell disease. Therefore, it is appropriate for healthcare practitioners to apprehend the genetic disorders and the explanation for their causes.
[/et_pb_text][et_pb_text _builder_version="4.9.3" _module_preset="default" width_tablet="" width_phone="100%" width_last_edited="on|phone" max_width="100%"]
| Subject | Biology | Pages | 7 | Style | APA |
|---|
Answer
Errors that can occur during Meiosis
Meiosis results in the reduction of chromosome numbers by half during cell division and this is essential in reproduction to ensure constant chromosome numbers in the offspring. However, its indispensable role in reproduction poses a great risk because any alteration in the genetic makeup of the parents is transmitted to the filial generations. This paper is purposely documented to discuss the errors that can occur during meiosis and provide the corresponding genetic changes and disorders.
The first stage of meiosis that involves DNA replication is prone to copying errors. The DNA replication errors result into disruption of gene sequences and the ultimate consequence is mutation of the genetic components. Mutations alter the final protein structures and hence, their functions also changes. Therefore, the mutations can lead to harmful effects or latent outcomes. An example of a DNA replication stage error disorder is the sickle-cell anemia. Hoban, Cost, Mendel, Romero, Kaufman, Joglekar, Ho, Lumaquin, Gray, Lill, and Cooper (2015) opine that the essential feature of sickle-cell disease is a single point gene mutation in the codon number seven of the β-globin gene sequence (p. 2597). The point mutation results in different protein structures that alter the functional components of hemoglobin. According to Voskaridou (2014), the point gene mutation results in the substitution of the glutamic acid residue with a valine residue in the β-globin chain that leads to the formation of the sickle Hemoglobin, HbS (p. 60). This assertion depicts that the initial alteration in genetic sequence during DNA replication can lead to sickle cell disease due to amino acid substitution. The associated symptoms for sickle-cell anemia include acute renal failure, ophthalmologic complications, and fever-infections.
Genetic errors can also during the recombination phase of meiosis. Homologous chromosomes exchange their genetic materials during the recombination phase. Baudat, Imai, and de Massy (2013) posit that the exchange of the genetic materials between homologous chromosomes during recombination contributes to the transmission transformed combinations of the linked alleles (p. 794). The homologous chromosomes align and pair exactly before, breaking, exchanging DNA portions, and rejoining. However, it is evident that there are errors that might result during the exchange of the genetic materials. Homologous chromosomes can misalign and the result would be one daughter cell have an extra chromosome while the other daughter cell would miss a chromosome leading to loss of some genetic material. The daughter cell with extra chromosome will have an over-expression of the genes located within the extra chromosome. Absence of meiotic recombination is as well an error of clinical significance. According to Tempest (2011), it is significance to apprehend achiasmate bivalents because lack of recombination foci result to sperm aneuploidy and consequent male infertility (p. 95). The sperm aneuploidy results to male infertility because there is mitigation of sperm production following the destruction of the abnormal sperms.
There is also a risk during meiotic recombination of pairing of non-homologous chromosomes that may lead to chromosomal translocation. Roukos and Misteli (2014) define chromosome translocation as the genome abnormality whereby a chromosomal segment breaks and either its portion or the whole of it integrates to a different chromosome (p. 293). Translocation reshapes gene sequence and in some cases, when the regulatory portions of DNA are involved, there occur misregulation of the genes. Consequently, there are several diseases associated with disproportionate gene segments or disturbed regulatory portions. Unregulated cell division due to chromosome translocations involving regulatory segments of DNA is likely to cause cancers. Cancer is basically the uncontrolled proliferation of cells. Roukos and Misteli (2014) also assert that chromosome translocations are remarkably associated with several human cancers, schizophrenia, and infertility (p. 293). The basis behind the disorders associated with the chromosome translocation is the creation of gene dosage imbalances after the chromosome translocations. Additionally, deletion of a portion of the chromosomes is an error that can also lead to permanent genetic change. Uzunhan, Sayinbatur, Caliskan, Sahin, and Aydin (2014) assert that a partial deletion, either interstitial or terminal, of the shorter arm of chromosome number 5 causes cri-du-chat (p. 209). Therefore, genetic deletion is of clinical significance as well.
The last stage where meiotic errors can occur is the chromosomal segregation step. The homologous chromosomes should segregate into gametes in such a way that all the gametes should have equal number of chromosomes that is half the original number in the parental cell. Under normal circumstances, the four chromatids of a meiotic tetrad will segregate completely with each of the four daughter cells receiving one chromatid. However, there could be errors that limit the separation of some homologous chromosomes. Consequently, some daughter cells will have more chromosomes than others after a failure of the homologous chromosomes to segregate. This chromosomal imbalance is the basis for clinical conditions such as trisomy. One of the effects of chromosomal trisomy is the Down’s syndrome. According to Li, Chang, Wang, Hirata, Papayannopoulou, and Russell (2012), Down syndrome results due to an extra copy of chromosome number 21 and has several clinical manifestations such as premature aging, heart defects, leukemia, and impaired cognition (p. 615). The resultant effects of the Down syndrome are manifested because of the extra chromosomal copies and the corresponding regulatory sequences. An individual with the Down syndrome disorder received an extra copy of chromosome number 21 from a parent. The basic argument is to demystify the influence of gene dosage on the phenotypic expression. Epstein and Holtzman (2013) argue that the higher the dosage for a particular gene, the greater the synthesis and the concentration of the ultimate gene product (p. 106). Therefore, the individuals with the trisomy for chromosome 21 will have increased expression of the genes coded in the chromosome 21.
The alternative consequence of inappropriate segregation is the inadequate number of chromosomes within the daughter cells after meiotic cell divisions. As one daughter cell receives an extra chromosome that did not segregate, the corresponding daughter cell will suffer from a deficit in chromosome number by the number of the extra chromosomes received by the counterpart. A specific example of such a disorder is the Turner syndrome. Hook and Warburton (2014) posit that the karyotype for Turner syndrome is 45; X and most embryos with the syndrome do not survive the gestational duration (p. 417). The 45; X karyotype confirms that the number of chromosomes in Turner syndrome are less than 46. The inadequacy of the chromosome number is due to the pair that did not segregate that moved to the corresponding daughter cell.
Another nondisjunction disorder is the Klinefelter syndrome. According to Groth, Skakkebæk, Høst, Gravholt, and Bojesen (2012), Klinefelter syndrome results in male due to an extra X chromosome and the associated symptoms include hypergonadotropic hypogonadism, small testis, and cognitive impairment (p. 20). The symptoms of hypogonadism are experienced because there would be an over-expression of the female characteristics due to an extra X chromosome.
In conclusion, the process of meiosis is not always perfect in the production of the daughter cell. Meiosis is prone to errors such as translocation, deletion, non-disjunction, and lack of recombination. These errors result in disorders that severe the lives of the victims. A vivid example is the change in genetic sequence that leads to the change in the β-globin change and thus, causing sickle-cell disease. Therefore, it is appropriate for healthcare practitioners to apprehend the genetic disorders and the explanation for their causes.
References
|
Baudat, F, Imai, Y, and de Massy, B 2013, 'Meiotic recombination in mammals: localization and regulation', Nature Reviews Genetics, 14, 11, pp. 794-806, Academic Search Premier, EBSCOhost, viewed 29 December 2015. Epstein, C.J and Holtzman, D. M 2013. The Molecular Genetics of Down Syndrome. Molecular Genetic Medicine, 2, p.105-120.
Groth, K.A., Skakkebæk, A., Høst, C., Gravholt, C.H. and Bojesen, A., 2012. Klinefelter syndrome—a clinical update. The Journal of Clinical Endocrinology & Metabolism, 98(1), pp.20-30.
Hoban, M.D., Cost, G.J., Mendel, M.C., Romero, Z., Kaufman, M.L., Joglekar, A.V., Ho, M., Lumaquin, D., Gray, D., Lill, G.R. and Cooper, A.R., 2015. Correction of the sickle cell disease mutation in human hematopoietic stem/progenitor cells. Blood, 125(17), pp.2597-2604. Hook, E.B. and Warburton, D., 2014. Turner syndrome revisited: review of new data supports the hypothesis that all viable 45, X cases are cryptic mosaics with a rescue cell line, implying an origin by mitotic loss. Human genetics, 133(4), pp.417-424.
Li, L.B., Chang, K.H., Wang, P.R., Hirata, R.K., Papayannopoulou, T. and Russell, D.W., 2012. Trisomy correction in Down syndrome induced pluripotent stem cells. Cell Stem Cell, 11(5), pp.615-619.
Roukos, V, and Misteli, T 2014, 'The biogenesis of chromosome translocations', Nature Cell Biology, 16, 4, pp. 293-300, Academic Search Premier, EBSCOhost, viewed 29 December 2015. Tempest, HG 2011, 'Meiotic recombination errors, the origin of sperm aneuploidy and clinical recommendations', Systems Biology In Reproductive Medicine, 57, 1/2, pp. 93-101, Academic Search Premier, EBSCOhost, viewed 29 December 2015. Uzunhan, T., Sayinbatur, B., Caliskan, M., Sahin, A. and Aydin, K., 2014. A clue in the diagnosis of Cri-du-chat syndrome: Pontine hypoplasia. Annals of Indian Academy of Neurology, 17(2), p.209-210.
Voskaridou, E 2014, 'Sickle cell disease complications', Thalassemia Reports, 4, 3, pp. 60-62, Academic Search Premier, EBSCOhost, viewed 29 December 2015.
|