Gene Mapping

Gene mapping describes identifying the location of specific genes on chromosomes. It is a key step in understanding genetic diseases. The goal of gene mapping is to understand and treat genes that cause genetic disease.

The Human Genome Project (HGP) was essentially completed in 2003. It was a 13-year project sponsored by the United States Department of Energy and the National Institutes of Health. Major contributions were made by China, France, Germany, Japan and Great Britain as well as others. Its goal was to build detailed guides to the type and location of all genes on chromosomes.

Every human being has 46 chromosomes. Twen-ty-three are inherited from the mother and 23 from the father of the child. The X and Y chromosomes make the essential difference between male and female. If the chromosomes that determine the sexual inheritance are both X then the child will be a female. If one is an X and the other is a Y the child will be a male. The other chromosomes contain the genes that regulate the growth and functioning of all of the cells in the human body.

The creation of a genetic map plotting the locations of genes on DNA strains of the respective chromosomes [Page 709]is the goal of gene mapping. A genome is the total set of genes on chromosomes. The genome may be that of a human (human genome) or a chicken or pig (chicken genome and pig genome). When researchers begin the process of gene mapping there is nothing on the map. As the genome is investigated the chromosomes are identified and the respective genes are also identified and their location plotted on their respective chromosomes. The end product is a complete map reporting the location of all the respective genome's genes and the DNA sequencing of the bases of each gene.

Genetic markers are fragments of DNA that identify differences in strains. The genetic markers are unique sequence-dependent patterns or DNA. The ordering of the different bases in genes is made by observing recombinant frequencies. The makers are somewhat like finger prints because of their unique characteristics.

It was estimated that there were between 50,000 and 100,000 genes in humans. However, the number of genes turned out to be much smaller. The number of genes is only between 20,000 and 25,000. The additional goal of determining the sequences of the three billion chemical base pairs that make up human DNA was also a goal.

There are two ways to do gene mapping—genet-ic mapping and physical mapping. Gene mapping identifies the order of genes along each chromosome. Genetic mapping analyzes the locus of genes on chromosomes. The locus of a gene (loci of genes) on a chromosome can allow it to be linked to another gene, in which case the two genes are “linked.” If genes are not linked to each other although linked to the chromosome then they are separated by an independent assortment.

Alleles are the sequences of chemical units that compose the genetic sequence of the gene. The loci may be the genetic inheritance of both the father and the mother of the human whose genetics are being mapped.

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