Rough Draft-Fragile X

Rough Draft-Fragile X - Introduction First discovered back...


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Introduction First discovered back in the 1970’s, Fragile X Syndrome is a genetic condition in which involves changes or mutations to the X chromosome. This illness is the most frequent kind of inherited mental retardation in males and also effects females but not to the same extent. There are many components that lead up the appearance of Fragile X Syndrome, for there are mutations and processes that must occur both on the chromosome and within the DNA segments. The syndrome is caused by the mutation of the FMR-1 or Mental Retardation 1 gene. Along with the actual mutation, there are unusual inheritance patterns of the symptoms; the unusual CGG repeats and the hairpin loops that are triggered by methylation are major components. As the amount of CGG expansion increases, so does the silencing and methylation of the actual FMR-1 gene. CGG repeats happen through inheritance to where there is a pre-mutation or a full mutation. The repeats then trigger methylation of genes and therefore do not produce the protein (FMRP) needed for brain development . Methylation is a very important process to understand while trying to make sense of Fragile X syndrome. Typically our bodies rely on methylation for certain events to occur such as protein synthesis. However, in a few cases methylation can be counterproductive and cause serious health problems that can be past down to younger generations. The lack of this process ultimately cuts down on the strength and number of connections that neurons have with the brain, naturally resulting in mental retardation. Chromosomes Chromosomes hold the genetic material contained to express genotypes and phenotypes. Chromosomes undergo many physical changes throughout the cell cycle; they must be
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translated, replicated, and divided before they can be passed on to children. It is in our chromosomes that genetic mutations occur, and are of great interest concerning Fragile X syndrome, as well as numerous other hereditary conditions. Chromosomes are made up of proteins and DNA. The proteins consist of histones which make the proteins positively charged. DNA is composed of two polymers on each side that run opposite from each other. The polymers are made up of smaller subunits called nucleotides, which have a nitrogenous base, phosphate groups, and five-carbon sugars. The two polymers are held together by the “backbone” of the DNA. The backbone of DNA is looks like a stepping ladder, and is made up of purines (Adenine and guanine) and pyrimidines (Cytosine and thymine) bases. The purine and pyrimidine bases are abbreviated A, G, C, T. These bases are what determines our genetic code; our phenotype and genotype. The binding sequence of purines and pyrimidine is adenine binds to thymine and guanine binds to cytosine in DNA. The DNA double helix is bound by the positively charged histones and the negatively charged phosphate groups while the backbone consists of the purine and pyrimidine pairs. However, in RNA the thymine is replaced by uracil. Humans contain 23 pairs of chromosome which are stored in the nucleus. Chromosomes
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This note was uploaded on 02/21/2012 for the course BIO 2450 taught by Professor Martin during the Spring '10 term at Texas State.

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