ASSIGNMENT

Assignment: Genetic Engineering



Assignment: Genetic Engineering

1)

Meiosis is one form of cell reproduction. This process is performed on the sex glands for the production of gametes. It is a process of division cell in which a diploid cell (2n) undergoes two successive divisions, with the ability to generate four haploid cells (n). In sexually reproducing organisms is important because it is the mechanism by which they produce the eggs and sperm (gametes). This process is carried out in two nuclear and cytoplasmic divisions, called first and second meiotic division or simply meiosis I and meiosis II. Both include prophase, metaphase, anaphase and telophase.

Overview of meiosis

At the interface is duplicated genetic material. In meiosis I the homologous chromosomes are divided into two daughter cells, is the phenomenon of inbreeding. In meiosis II, as a mitosis, chromatid migrates each pole. The result is four haploid daughter cells (n).

During meiosis members of each pair of homologous chromosomes during prophase are paired, forming bivalent. During this phase a protein structure called a synaptonemal complex, allowing recombination occurs between homologous chromosomes. Subsequently there is a large divalent chromosome condensation and the plates are situated in the equatorial during the first metaphase, leading to the migration of chromosomes in each of the poles during the first anaphase. This reduction division is responsible for the maintenance of chromosome number characteristic of each species. In meiosis II, the sister chromatids comprising each chromosome separate and are distributed between the nuclei of the daughter cells. Between these two successive steps there is the S (replication of DNA). The maturation of the daughter cells will result in the gametes (Nicholl, 1994, pp. 50).

Meiosis and life cycle

Sexual reproduction is characterized by the fusion of two sex cells haploid to form a zygote diploid , so it follows that, in a sexual life cycle, meiosis must occur before gametes originate.

In animals and in few other organisms, meiosis immediately precedes the formation of gametes . The somatic cells of an individual organism multiply by mitosis and are diploid, haploid cells are the only gametes. These are formed when some germline cells undergo meiosis. Gamete formation called gametogenesis . The male gametogenesis, termed spermatogenesis , leads to the formation of four haploid sperm for each cell that enters meiosis.

In contrast, the female gamete, called oogenesis, generates one egg for each cell that enters meiosis, a process that virtually all cytoplasm assigned to only one of the two cores in each meiotic division. At the end of the first meiotic division retained a core, the other, called the first polar body, is excluded from the cell and finally degenerates. Similarly, the second end of the core division becomes the second polar body and the other core survives (Williamson, 1981, pp. 61). Thus, a core becomes haploid receiver most of the cytoplasm and cell nutrients meiotic accumulated original.

However, although meiosis is performed somewhere in the sexual life cycle, not always directly precedes the formation of gametes. Many simple eukaryotes (including some fungi and algae ) remain haploid ...