Explain the concept of linkage and gene mapping.

Linkage refers to the tendency of genes located close together on a chromosome to be inherited together, and gene mapping is the process of determining their relative positions.

Linkage is a fundamental concept in genetics. It was first proposed by Thomas Hunt Morgan, who observed that certain traits in fruit flies seemed to be inherited together more often than would be expected by chance. This led him to the idea that these traits must be located on the same chromosome, and thus are 'linked'. The closer two genes are on a chromosome, the more likely they are to be inherited together, because they are less likely to be separated during the process of recombination, which occurs during meiosis.

Gene mapping, on the other hand, is the process of determining the relative positions of genes on a chromosome. This can be done using a variety of techniques, including linkage analysis, which involves studying the inheritance patterns of traits in families to determine how closely linked certain genes are. The closer two genes are, the more likely they are to be inherited together, and thus the higher the 'linkage' between them. This can be used to create a 'map' of the genes on a chromosome.

Another method of gene mapping is physical mapping, which involves directly studying the DNA of a chromosome to determine the exact locations of genes. This can be done using techniques such as DNA sequencing or fluorescence in situ hybridisation (FISH), which involves using fluorescent probes to bind to specific sequences of DNA.

In summary, linkage is the concept that genes located close together on a chromosome are likely to be inherited together, and gene mapping is the process of determining the relative positions of these genes. Both of these concepts are fundamental to our understanding of genetics and have been instrumental in many important discoveries in the field.