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Within each living thing on our planet, there is a complete set of plans for making another such organism. This is called the genome. It contains the master blue print for all activities and structures on the cellular level. These genomes can be found in the nucleus of every cell in an organism. The human genome consists of coiled threads of DNA (DeoxyriboseNucleicAcid) and their associated protein molecules. This combination of DNA and protein forms a cell's chromosomes. DNA (DeoxyriboseNucleicAcid) DNA molecules come in the shape of a double helix, with sides composed of sugar and phosphate molecules. the "rungs" of the twisted ladder that is a DNA helix are composed of bases which are chemicals containing the element nitrogen. The DNA strands are actually a linear pattern of repeating sets of one sugar, one phosphate, and one base. These sets are called nucleotides. Four different bases are present in human DNA:
The Specific order of the bases, as arranged against the sugar and phosphate spine of the helix is referred to as the DNA sequence. The function of a DNA sequence is to specify the exact genetic instructions necessary to create an individual life-form, with its own characteristics. The two spines of the helix are held together by weak bonds between the bases on either side. This forms base pairs, which are used when telling the size of a genome. The human genome, contains approximately 3 billion base pairs. There are only two types of pair, an A-T (one Adenine and one Thymine) or a C-G (one Cytosine and one Guanine.) During reproduction, this pattern is followed strictly to minimize in the resulting organism and its future generations. Genes Contained within each DNA molecule are many genes, the basic units of heredity, both physical, and functional. A gene can be defined as a specific sequence of nucleotide bases, which carries the information necessary for building proteins. Proteins are the structural components of cells and tissues as well as acting as necessary enzymes for essential biochemical reactions. There are an estimated 80,000-100,000 genes in the human genome. Although human genes vary greatly in length, 10% of each gene includes the protein coding sequences or "exons". Interlaced with the exons are the "intron" sequences, which have no coding functions. The remaining pieces of the genome are thought to consist of other regions such as obscure control sequences and intergenic regions, which have no coding function. All living organisms are composed mainly of proteins. Humans can create approximately 80,000 different types in their bodies. Proteins can further be broken down into long chains of "amino acids". Twenty types are typically found in proteins. In each gene every different, specific chain of three DNA bases, or "codons", directs the manufacturing of proteins. Since 3 bases code 1 protein amino acid, a human gene with 3000 base pairs will create approximately 1000 amino acids. The genetic code, therefore, is a set of codons which dictates what amino acids make up specific types of proteins. These instructions are transmitted by way of mRNA (messengerRiboNucleicAcid) an intermediate molecule similar to single strand of DNA. Chromosomes All base pairs in the human body, approximately, 3 billion, are organized into 24 individual types of chromosomes, in 23 pairs. All of an organism's genes are arrange linearly along the chromosome. Most human cells contain 2 sets of chromosomes within their nucleus. Each set consists of 23 single chromosomes, 22 autosomes and 1 other. A male will have a "Y" chromosome, and an "X" chromosome, one in one pair, and the other in the other pair. While a female will have two "X" chromosomes, one in each pair. A chromosome is comprised of approximately equal parts of DNA and protein. Differences in the physical properties such as size and patterns of bonding, allow the chromosome to be distinguished from one another. This is done by a process called a "karyotype". There are several types of major chromosomal abnormalities, including missing or extra copies, gross breaks, and trans-locations, or re-joinings; which can be detected by examination of the chromosomes with a mircosope. However, Downs Syndrome and a few genetic diseases can only be detected with a karyotype cannot detect all diseases. Most, in fact, are too subtle to even be detected without a molecular analysis. These mutations are responsible for many hereditary diseases, such as cystic fibrosis, and sickle cell anemia. These mutations may also predispose an individual to cancer, a psychic disease, or different, another complex medical condition. There are three types of chromosomes:
By doing this along with storing the bands, cytogenetisists are able to determine the different chromosomes from one another.
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