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By finding recombination frequencies for many gene pairs, we can make linkage maps that show the order and relative distances of the genes on the chromosome.
Physical maps specify the distances between landmarks along a chromosome. Ideally, the distances are measured in nucleotides, so that the map provides a direct description of a chromosomal DNA molecule. The most important landmarks in physical mapping are the cleavage sites of restriction enzymes.
Gene maps help describe the spatial arrangement of genes on a chromosome. Genes are designated to a specific location on a chromosome known as the locus and can be used as molecular markers to find the distance between other genes on a chromosome.
There are two main ways to map a genome: genetic mapping and physical mapping. They’re used to identify and record the location of genes and the distances between genes on a chromosome. A genome map highlights the key ‘landmarks’ in an organism’s genome, helping scientists to navigate their way around the genome as they sequence it.
Chromosomal map. In a chromosomal map, genes or other identifiable DNA fragments are assigned to their respective chromosomes, with distances measured in base pairs.
Map Distance Over Long Chromosomes. Map distances are always calculated for one pair of loci at a time. However, by combining the results of multiple pairwise calculations, a genetic map of many loci on a chromosome can be produced (Figure 11.2.2). A genetic map shows the map distance, in cM, that separates any two loci, and the position of ...
The human genome is distributed among 24 chromosomes (22 autosomes and the 2 sex chromosomes), each containing between 5 × 10 4 and 26 × 10 4 kb of DNA ( Figure 4.26 ). The first stage of human gene mapping is the assignment of known genes to a chromosomal locus, usually defined as a metaphase chromosome band.
