DNA Essay Example | Topics and Well Written Essays - 1000 words

DNA - Essay Example Production of gametes through meiosis A basic tenet of embryology is the fusion of a male and a female gamete in the process called fertilization. The gametes are haploid cells that are produced in the testes and ovaries of the father and mother, respectively. They are produced in a cell division process called meiosis. This process is special because each of the resulting daughter cells contains just half of the chromosomes of the parent cell. In effect, a child receives 50% of each of the parent’s genetic material. Briefly, it involves two major processes, Meiosis I and then II, each composed of the usual processes of (1) prophase that prepares for (2) metaphase, in which the chromosomes meet in the middle, (3) anaphase, whereby the chromosomes separate and go to two opposite ends of the dividing cell, and (4) telophase, in which the cell membranes separate to ultimately produce the daughter cells. Initially, the gonium is a diploid cell (chromosome number (n) = 46) with rep licated chromosomes in the form of sister chromatids. After Meiosis I, the daughter cells are already haploid (n = 23), because what is separated during Anaphase I are the pairings of homologous chromosomes. Each chromosome carries genes for specific traits, and each chromosome of a homologous pair thus carries an allele per trait. In contrast, during Anaphase II, the sister chromatids separate, producing haploid cells with unreplicated chromosomes. Ideally, 4 daughter cells are produced per meiosis of a –gonium, and this is what happens in the production of sperm cells. However, in the case of female gamete formation, 2 daughter cells (1 from meiosis I and 1 from meiosis II), only 1 oocyte is produced from a cycle of meiosis (Campbell and Reece, 2002). DNA replication occurs in preparation for cell division How does DNA replicate? A part of the double-stranded DNA (dsDNA) unwinds, allowing DNA polymerase and DNA ligase to get into what is known as the replication bubble. The DNA polymerase adds the complement of each nucleotide in the parent strand, completing the whole length of the strands to produce two semi-conservative dsDNA, each composed of a parent strand and a daughter strand. Eventually, these two identical dsDNA, takes the form of sister chromatids, which are separated during mitosis, the somatic cell replication. The resulting daughter cells thus get identical copies of DNA, which is an exact match to the parent cell (Campbell and Reece, 2002). DNA is the genetic code that directs all cellular function Why is it necessary for each cell to bear DNA? The DNA, housed in the nucleus, is the template to produce messenger RNA (mRNA) through a process called transcription. In this process, a transcription factor recognizes the TATA sequence 25 nucleotides upstream from the transcriptional start point. This initiates the binding of RNA polymerase II to the DNA, and binding of additional transcriptional factors, opening up the double strand to produ ce the pre-RNA strand from 5’ to 3’. The pre-mRNA then peels off from the DNA template, and it complete detaches hundreds of nucleotides after reaching the terminating AAUAAA sequence. This undergoes further