The Role of Genes
The Role Of Genes
Every organism, inclu
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Every organism, including human beings, has a genome containing all the biological information required to build and maintain a living example of that organism (NCBI, 2004). The biological information contained in the genome is encoded is deoxyribonucleic acid (DNA), and is divided into discrete units known as genes. The term "gene" was coined in 1909 by Danish botanist Wilhelm Johanssen for the heredity unit found on a chromosome. A single gene consists of a unique sequence of DNA that provides the instructions for making a functional product - a protein. Genes instruct each cell type to make discrete sets of proteins at just the right time, and this specificity leads to unique organisms being formed. Genes also code for proteins that attach to the genome at the appropriate positions and switch on a series of reactions called gene expression. Not all genes are present in the nucleus. Cell organelles known as mitochondria possess their own genetic material which differs from nuclear genetic material in that it is all maternally derived: nuclear DNA is inherited half from the father and half from the mother (NCBI, 2004). This is because although there are mitochondria in the tail of sperm, the tail breaks off when the sperm enters the egg during fertilization, so all the mitochondria of the fertilized egg come from the maternal egg cytoplasm. Also, there is no recombination in mitochondrial DNA so there is no shuffling of genes from one generati
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example of genetic control at work. Skin color is determined by the amount of melanin found in skin cells, which is controlled by two genes that control the production of melanin, each of which has a dominant and a recessive expression (Genetic, 2005). This gives 16 possible combinations of genotype when coding for skin color. Although there are 16 different combinations of expressing the skin phenotype, there are five different genotypes that the genes for melanin can express. Each expression of melanin has an accumulating effect on skin tone until maximum expression of melanin through four dominant alleles leads to black skin phenotype:
M1M1M2M2 genotype = black skin phenotype
M1M1M2m2 genotype = dark brown phenotype
M1M1m2m2 genotype = brown phenotype
M1m1m2m2 genotype = light brown phenotype
m1m1m2m2 genotype = white phenotype
A person will be born with one of these five skin colors. After birth, external factors such as exposure to UV radiation from sunlight will change the color of the skin from its original genetic expression.
The gene for albinism in humans is an epistatic gene, meaning that it masks the phenotypic effect of another gene (NCBI, 2004). It is not part of the skin color gene, but its
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Wilhelm Johanssen, Retrieved Apr, Western Blotting, Law Dominance, Kohler Milstein's, Genetic Information, Cdc6 Mcm5, Genetic Variation, Region LCR, M13 Lesney, monoclonal antibodies, ncbi 2004, lesney 2001, retrieved apr, m1m1m2m2 genotype =, phenotype m1m1m2m2, m1m1m2m2 genotype, 18 2005, apr 18, genotype =, retrieved apr 18, monoclonal antibody, apr 18 2005, phenotype m1m1m2m2 genotype, apr 15 2005,
Approximate Word count = 5190
Approximate Pages = 21 (250 words per page)
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