List some of the methods for physically mapping genes and explain how
they are used to position genes on chromosomes.
Mapping of Genes:
The technique of gene mapping methods are used to identify the location of the gene and also to determine the distance between the genes. The map generated by the process of gene mapping is called as Genome Map.
A genome map signifies the location of the molecular markers on chromosomes.
Genome map can be made through two processes
- Genetic Mapping
- Physical Mapping
Genome map determines the position (locus) of the genes based on the frequency or degree of recombination. Through genetic mapping, inheritance of genes and assortment of the genes.
In Physical mapping, molecular biology is being used and then genome maps are created. This physical genome map signifies the position of the sequences and the actual physical distance between the loci of genes. This distance between the loci is measured in Base Pair (bp).
Methods for physically mapping genes:
- Restriction Maps
- FISH
- STS
Restriction Maps:
These restriction maps are the description of the restriction sites which are the cleavage sites for the enzyme restriction endonuclease in a DNA fragment.
Here, in restriction enzyme is used as a tool for restriction mapping which determines the number of the restriction sites present along with their position on the DNA.
Two methods by which restriction maps are generated:
First is to identify whole sequence of the DNA and then through a computer program, we need to put the DNA sequence information in the computer program then it will give the information about the restriction sites presence for restriction enzyme.
In second approach, the DNA fragment is first treated by a restriction enzyme and then after that by some other restriction enzyme and these cleaved fragments are again treated by the mixture of the restriction enzymes i.e., double restriction digestion is done. Now based on the length of the DNA fragments positions of the restriction sites are determined and studied. DNA is not only used but with the help of a plasmid or bacteriophage (which DNA sequence is already known) mapping is done.
Gel Electrophoresis is used to determine the lengths of the DNA.
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