Thursday, August 20, 2015

Genetics 101: Basic genetics and inheritance of Porphyria

Genetics 101:  Basic genetics and inheritance

In order to better understand the Porphyrias and how the disorders are inherited, it is helpful to understand some concepts of basic genetics and inheritance patterns.

DNA, Chromosomes, and Genes:

Deoxyribonucleic acid (DNA) is a nucleic acid that contains the instructions used in the development and functioning of all known living organisms and some viruses. DNA is often compared to a set of blueprints or a recipe or a code because it contains the instructions needed to make certain proteins, which are the complex molecules that do most of the work in our bodies. Each of these proteins has a specific function in the cell, and, ultimately in how the organism develops, its physical makeup, and how it functions day-to-day. The DNA segments that carry this genetic information are called genes. The size of each gene varies greatly, and there are about 20,000 genes that are distributed along the 23 pairs of chromosomes.
A DNA molecule is a twisted double-strand of building blocks, called nucleotides.  It is like a twisted ladder, with the vertical stringers made of phosphates and sugars and the rungs made of pairs of nucleotides. There are four nucleotides in DNA:  adenine (A), thymine (T), guanine (G), and cytosine (C). Also important is that on each rung of this ladder, A always pairs with T, and G always pairs with C. These nucleotides along the ladder are like letters in a word, and put together in their specific order make up the words in a detailed set of instructions. These instructions are read using a special code, called the genetic code.
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GenGenome Management Information System,
Oak Ridge National Laboratory
http://genomics.energy.gov
DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone.
Within cells, DNA is organized into long structures called chromosomes. A chromosome is like a cookbook with many recipes (or genes) that tell the body how to function. The human body is made up of trillions of cells and over 200 different cell types like various blood, liver, and brain cell types.  Each cell contains 46 chromosomes. Each chromosome can be identified by its relative size and location of the centromere, a constriction in the chromosome. 


http://www.rarediseasesnetwork.org/porphyrias/patients/genetics101/index.htm

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