Cell Division and Gene Expression - Essay Example

Cell Division and Gene Expression The abnormality of the genes and chromosomes causes the genetic disorders. The genetic disorders are also caused by the environmental factors. Every human must contain 23 pairs of chromosomes in their cells. If any increase or decrease in the 23 pairs leads to genetic disorders. The absence or presence of an extra arm of a chromosome leads to disorders. Genetic disorders are caused by many mechanisms. Some of the mare mutations, aneuploidy, deletions, duplications, inversions and trans locations.

During the Anaphase II condition, the homologues must separate from each other to form sister chromatids, but due to non disjunctions they fail to separate from each other. (Kornberg and Baker, 2005). This results in the gametes having two copies of one chromosome and no copy of the other chromosome. This condition is termed as aneuploidy. This abnormal chromosome number results in two conditions: monosomy and trisomy. The presence of an extra copy number of chromosome, leads to genetic disorders such as trisomy 21, trisomy 13 and trisomy 18.

(Kornberg and Baker, 2005). These trisomic conditions are based on the autosomes. (Richards and Hawley, 2010). The genetic diseases associated with the sex chromosomes include klinefelter syndrome, Trisomy X and monosomy X. (Kornberg and Baker, 2005). The chemical information about how a human being should be both their physical and mental characteristics are decided by the nucleotide arrangement present inside the cells. A change in the base pair in the Deoxy ribo nucleic acid (DNA) will result in the change in the characteristics of the person.

These DNA constitute the genes. Each gene codes for the production of specific enzyme that plays an important role in biochemical reactions. These DNA are tightly wound on the histones to form a thicker arm. (Richards and Hawley, 2010).These arms join to for m the chromosomes. The tight winding of the DNA forms the 23 pairs of chromosomes of which 22 pairs are autosomes and one pair is sex chromosomes. Trisomy X is the chromosomal condition that has an extra part of chromosome 21 along with the 23 pairs of chromosome.

This condition is also called as Down syndrome. (Richards and Hawley, 2010). The presence of this extra chromosome results in impairment of growth and cognitive ability. A part of the facial characteristics are also changed. The children with this defect are able to survive after birth for some time. The other trisomy conditions also give a chance for the child to survive with the defects. (Kornberg and Baker, 2005). The replication of the DNA is the important part of the cell cycle. This occurs at the interphase of the cell cycle.

At the interphase region, the cell accumulates the nutrient requirements and also produces a copy of the chromosomes. The cell cycle is made up of four phase. G1 phase, S phase, G2 phase and M phase. (Kornberg and Baker, 2005). The G2 phase is called as the interphase. The DNA strand unwinds from its compact nature into a linear strand and the replication occurs. Here the copy of the DNA is produced at the end of replication. The DNA replication occurs at the synthesis phase (S phase). (Kornberg and Baker, 2005).

At the end of the S phase, DNA strands compresses to form the chromosomes. This chromosome then moves to the daughter cells and the cell division occurs. The DNA replication thus passes the genetic information from the parent to the daughter cells. (Kornberg and Baker, 2005). The Chromosomes are formed just before the cell division. The Chromosomes will get condensed to enable the cell division to occur at ease. Two types of chromosomes are present in the cell; they are replicated chromosomes and the parent chromosomes.

After the prophase I comes the metaphase I where the spindle fibers are formed at the ends and pull the chromosomes to the equator. (Tobin and Dusheck , 2005). This results in the separation of the replicated chromosomes from the mother chromosomes. Some mechanism keeps the replicated chromosomes very intact and the chromatids are tightly packed. The telophase I and the cytokines follow them rapidly and the daughter cells undergo the meiosis. (Tobin and Dusheck , 2005). Because of the sorting out that occurs between the replicated chromosomes, genetic diversity occurs in the humans.

The alignment of the pairs is very independent. The crossing over and the random alignment results in the genetic diversity in the humans. (Tobin and Dusheck , 2005). In mitotic cell division, the replicated chromosomes have diploid number of chromosomes. Where as in meiosis, the replication occurs at the metaphase I , forming a bivalent. This bivalent crosses the genetic information between the chromosomes. During the anaphase I, the replicated chromosomes separate again and move to the opposite ends.

This time they contain only haploid number of chromosomes. (Richards and Hawley, 2010). Only one set of replicated chromosomes will be present in the cell. At the Telophase I stage of sex cells, they have neither haploid nor diploid cells but an intermediate stage. (Richards and Hawley, 2010). Anaphase stage is very important for the recombination of the replicated chromosomes to occur. It is only during the anaphase stage, the replicated chromosomes become very intact and separate from each other.

References Kronberg, A and Baker, T. A. (2005). DNA Replication. London: University Science books. Richard, J. E. and Hawley, R. S. (2010). The Human Genome : A user’s guide. New York: Academic press. Tobin, A. J. and Dusheck, J. (2005). Asking about life. London: Cengage learning.