Deletion mapping
Encyclopedia
In genetics
and especially genetic engineering
, deletion mapping is a technique used to ascertain the location of mutation
sites within a gene
.
The principle of deletion mapping involves crossing a strain who has a point mutation
in a gene, with multiple strains who each carry a deletion
in a different region of the same gene. Wherever recombination
occurs between the two strains to produce a wild-type (+) gene (regardless of frequency), the point mutation cannot lie within the region of the deletion. If recombination cannot produce any wild-type genes, then it is reasonable to conclude that the point mutation and deletion are found within the same stretch of DNA
.
This example should demonstrate how the principle works:
Suppose you have a gene X, which in wild-type (+) form can be shown linearly like so:
5'-------------------------------------------------------------------------------------------------------------------3' gene X, +
Suppose a strain of organisms has a point mutation in the gene (now called gene X, – to denote that it is no longer wild-type):
5'----------------------------------------------------X--------------------------------------------------------------3' gene X, –
Now suppose you have two strains of organisms, each with deletions in gene X at different sites, called del-1 and del-2, respectively (the dotted line indicates the site of deletion):
5'-------------------(..............................................)------------------------------------------------3' del-1
5'------------------------------------------------------------(............................................)---------3' del-2
Because the point mutation lies within the deletion of del-1, there will be no wild-type (+) recombinants between the point mutant and the del-1 mutant. However, in a cross between the point mutant and the del-2 mutant, there could be a successful wild-type (+) recombinant produced.
In genetic recombination, if a mutant allele in the donor is within the sequence corresponding to the region deleted in the recipient, then no (+) recombinants will be obtained (as in the cross with del-1). To repair a deletion by recombination, the donor must have wild-type DNA sequence in the region corresponding to the DNA deleted in the recipient (as in the cross against del-2). In other words, there is a feasible recombination possibility between the point mutant and del-2 in which a length of DNA could be made that contained neither the point mutation, nor the deletion, indicating that the mutations in these two strains cannot be in the same region.
Note that not all crossovers between the point mutant and del-2 will yield (+) recombinants; in this case only those crossover events that occur between the point mutant and the 5' end of the deletion would inherit the wild-type sequence.
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
and especially genetic engineering
Genetic engineering
Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...
, deletion mapping is a technique used to ascertain the location of mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
sites within a gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
.
The principle of deletion mapping involves crossing a strain who has a point mutation
Point mutation
A point mutation, or single base substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA. Often the term point mutation also includes insertions or deletions of a single base pair...
in a gene, with multiple strains who each carry a deletion
Deletion
Deletion is the act of deleting or removal by striking out material, such as a word or passage, that has been removed from a body of written or printed matter.Deletion may refer to:*File deletion, a way of removing a file from a computer's file system...
in a different region of the same gene. Wherever recombination
Recombination
Recombination may refer to:* Recombination , the process by which genetic material is broken and joined to other genetic material* Recombination , in semiconductors, the elimination of mobile charge carriers...
occurs between the two strains to produce a wild-type (+) gene (regardless of frequency), the point mutation cannot lie within the region of the deletion. If recombination cannot produce any wild-type genes, then it is reasonable to conclude that the point mutation and deletion are found within the same stretch of DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
.
This example should demonstrate how the principle works:
Suppose you have a gene X, which in wild-type (+) form can be shown linearly like so:
5'-------------------------------------------------------------------------------------------------------------------3' gene X, +
Suppose a strain of organisms has a point mutation in the gene (now called gene X, – to denote that it is no longer wild-type):
5'----------------------------------------------------X--------------------------------------------------------------3' gene X, –
Now suppose you have two strains of organisms, each with deletions in gene X at different sites, called del-1 and del-2, respectively (the dotted line indicates the site of deletion):
5'-------------------(..............................................)------------------------------------------------3' del-1
5'------------------------------------------------------------(............................................)---------3' del-2
Because the point mutation lies within the deletion of del-1, there will be no wild-type (+) recombinants between the point mutant and the del-1 mutant. However, in a cross between the point mutant and the del-2 mutant, there could be a successful wild-type (+) recombinant produced.
In genetic recombination, if a mutant allele in the donor is within the sequence corresponding to the region deleted in the recipient, then no (+) recombinants will be obtained (as in the cross with del-1). To repair a deletion by recombination, the donor must have wild-type DNA sequence in the region corresponding to the DNA deleted in the recipient (as in the cross against del-2). In other words, there is a feasible recombination possibility between the point mutant and del-2 in which a length of DNA could be made that contained neither the point mutation, nor the deletion, indicating that the mutations in these two strains cannot be in the same region.
Note that not all crossovers between the point mutant and del-2 will yield (+) recombinants; in this case only those crossover events that occur between the point mutant and the 5' end of the deletion would inherit the wild-type sequence.