Gene mapping

A gene map shows the linear arrangement of genes in the genome of an organism. We distinguish genetic and physical genetic maps here. The order of loci is registered on a genetic map. On a physical gene map of the exact distances between genes are measured in base pairs entered.

Although the arrangement of the genes is the same on both types of cards, there are no universally valid " conversion formula " between the two types of cards. The reason for this is that recombination frequencies vary extremely widely depending on the region of the genome and, depending on gender.

In order to obtain a complete physical map of the viral genome sequence of an organism must be known. From this can be estimated also, how many genes are contained in the genome.

Linkage map or genetic map

For one, you can linkage maps ( maps linking / linkage maps) to create. The crossover rate is a measure of the distance between two gene loci: By crossover genes are separated from one another. If two genes close together, so a separation is less likely than if they are far apart. A linkage map is created by analysis of recombination and are merely the order of genes on a chromosome and no precise location information again.

The mapping unit is a centiMorgans here. 1 cM represents a recombination frequency of 1%. ( If the recombination of two genes at 16 %, as is their genetic distance 16 cM ). The less frequently recombine genes, the closer the studied loci together. At a distance of 50 cM ( recombination rate of 50%, about one-third of the chromosome length) the loci are considered uncoupled, ie one can not determine whether two genes are on a chromosome or not by simple linkage analyzes.

Cytological chromosome map or physical map

On the other hand, you can create cytological maps of chromosomes with other methods that reflect the physiological location of genes on a chromosome. To create cytological chromosome maps are not operated for the evaluation of recombination, but for example the microscopic visualization ( in situ hybridization, FISH ) of known genes. The distance between two genes on a cytological map is given in m ( microns ). There are various procedures, such as the extraction of DNA fragments by restriction enzymes with subsequent arrangement of the fragments. The arrangement of the fragments leads to a problem known bioinformatics problems, such as the Double Digest.

S is a DNA sequence. A physical map consists of a set of markers M and an image, which assigns to each marker in a position S M

Comparison

Although the comparison of linkage maps and genetic maps cytological match the order of the genes examined, but not their location on the chromosome. This is due to a fact that crossing-over events occur more frequently in some areas of a chromosome, than in others. There are gender -specific differences in recombination frequency on the other.