Gene mapping, aka DNA mapping began in 1911 with Edmund B. Wilson. He proved his theory that the gene for colorblindness was on the X chromosone because of its distinctive pattern of inheritance. Fathers do not pass it on to sons, and women rarely are colorblind. He discovered that the X chromosome was distinguishable by its size; females have two copies and males only one (7). According to Robert Cook-Deegan, for fifty years, study of the inheritance patterns of X-linked disease remained the most reliable gene mapping method. The first gene mapping of a human disease trait on another chromosome was published until 1968 (8).
How does gene mapping occur?
DNA should be thought of as two intertwined chains, which form a ladder. The ladders are made up of four rungs, or nucleotides bases. The four nucleotide bases are adenine (A), guanine (G), cystosine (C), and thymine (T). The bases form a four-letter-code that yields our genetic information. Each nucleotide base has a complimentary base. A pairs only with T, and G pairs only with C. In 1977, two ways for deciphering the DNA code were developed. Fredrick Sanger method is the most popular. First the strands of DNA are "unzipped," yielding two single strands of nucleotides. One single strand is chosen as the template and is replicated. A little piece of known code is tacked on to each on the strands of DNA. The template strands are separated into four groups so each can be subjected to slightly different reaction (9).
