Genetics Primer - Introduction
Please note that the information provided in this genetics primer is intended to serve as a general information source. It should not be used as a substitute for consultation with doctors, specialists or genetic counselors. Introduction
The "Central Dogma of Molecular Biology: DNA > RNA > Protein The "Central Dogma" of molecular biology is that DNA is transcribed into RNA, which is translated into protein. A gene is a region of DNA encoding the information to produce RNA, which in turn encodes a protein. Each gene consists of a coding sequence that defines the protein as well as a sequence that directs the processing of DNA into RNA. DNA is made up of four nucleotides: - Adenine (A)
- Guanine (G)
- Thymine (T)
- Cytosine (C)
These nucleotides are repeated in various patterns of three, called codons, each indicating a specific amino acid. The order and type of codons in RNA code a sequence of amino acids and thereby determine the type of protein that will be produced. DNA is packaged in the two sets of 23 chromosomes found in normal somatic cells. One set of 23 chromosomes is inherited maternally, the other paternally. In this way, offspring receive two copies of each gene (the two copies may or may not be identical and are referred to as "alleles"). An exception to this rule is the inheritance of sex-linked genes. The X- and Y-chromosomes, making up the 23rd pair of chromosomes, determine the gender of an individual. (The chromosomes making up the first 22 pairs are called the autosomal chromosomes.) A female has inherited X-chromosomes from both her mother and father and thus has two copies of each gene on the X-chromosome. A male has inherited an X from his mother and a Y from his father and thus has only one copy of the genes on the X-chromosome. The inheritance of mitochondrial DNA provides an additional exception; located in the mitochondria rather than in the nucleus of a cell, mitochondrial DNA is inherited exclusively from the mother.
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