In
genetics
Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinians, Augustinian ...
and especially
genetic engineering
Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of Genetic engineering techniques, technologies used to change the genet ...
, deletion mapping is a technique used to find out the
mutation
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, ...
sites within a
gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
.
The principle of deletion mapping involves crossing a strain which has a
point mutation
A point mutation is a genetic mutation where a single nucleotide base is changed, inserted or deleted from a DNA or RNA sequence of an organism's genome. Point mutations have a variety of effects on the downstream protein product—consequences ...
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
The wild type (WT) is the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard "normal" allele at a locus, in contrast to that produced by a non-standard, " ...
(+) 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
Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
.
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.
Genetic engineering
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