Monday, July 29, 2019

Meiosis; Asexual and Sexual Reproduction; History of Genetics; Assignment

Meiosis; Asexual and Sexual Reproduction; History of Genetics; - Assignment Example Meiosis The process of meiosis is divided into two segments; Meiosis I and Meiosis II. Meiosis I is similar to mitosis and consists of Prophase I, Metaphase I, Anaphase I and Telophase I. When the first division comes to an end, there is the formation of two daughter cells and each contains 23 chromosomes and has undergone crossing over. Crossing over is the exchange of genetic material between two chromosomes. Meiosis II consists of the same stages. However the end stage produces four daughter cells each having a different genetic make-up. All four cells convert into sperms in males while in females only one matures as egg or ovum. As mentioned earlier, meiosis plays a very important role in sexual reproduction by causing genetic variations in the offspring. It reduces the number of chromosomes in the parent cells which are egg and sperm, collectively called as gametes or sex cells. Because of this reduction each cell contains only one set each. A process of independent assortment takes place where each allele gets different chromosome varying at any specific locus. Secondly, it also allows crossing-over which results in genetic mix-up between the two parental chromosomes and we see genetic variations in the offspring. Asexual and Sexual Reproduction Asexual reproduction is defined as a type of reproduction where the organism produces an exact copy of itself without any genetic variation or involvement of any other individual. Different organisms reproduce asexually in various manners. For instance bacteria reproduce by binary fission and the yeast by budding. Fragmentation, spore formation and vegetative reproduction are some other forms of asexual reproduction. Sexual reproduction, on the other hand, is a process where two parent organisms create an offspring that has a combination of genetic material from both the parents. Most of the animals and plants reproduce sexually. However there are certain organisms that reproduce both sexually and asexually like star fish, sea anemones, slime molds and aphids. Organisms that reproduce asexually can create descendents in large numbers but since the offspring have very few DNA variations they are all equally vulnerable to diseases. However sexually reproducing organisms undergo genetic variations and the species are stronger in withstanding the harsh environment. The sexual organisms also produce lesser amount of offspring. Because of this reason the organisms that reproduce through both ways, switch towards sexual reproduction under unfavorable conditions. This helps them in acquiring the genetic variations that facilitate them in adapting to the surroundings. However sexual reproduction is an energy requiring process in contrast to asexual reproduction which requires minimal amount of energy. To explain the extensive use of sexual reproduction by organisms, George C. Williams used the example of lottery tickets. Sexual reproduction is like buying few tickets of different numbers which increases the chance of winning. While asexual is like buying loads of tickets with same numbers. This theory is not considered now because of newfound evidences. History of Genetics History of genetics can be traced back to 1866 when the work of Gregor Johann Mendel on pea was pu blished and his theory was recognized as Mendelian Inheritance. He was the first to study the genetic inheritance patterns in the peas and the fact that they followed a certain rule. After this breakthrough in the world of genetics different such theories came into sight. One considerable work was done in 1900 by Hugo de Varies, Carl Correns and Erich von Tschermak and was

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