Sequence inversion, in the context of genetics, is a type of chromosomal rearrangement where a segment of DNA is flipped or reversed within the sequence, and the reversed segment is the reverse complement of the original sequence.
Understanding Sequence Inversion
Imagine a DNA sequence as a string of letters. Inversion occurs when a section of that string is cut out, reversed, and then reinserted back into its original location. Critically, this process also involves taking the reverse complement of the inverted sequence.
Key Characteristics
- Reversal: The order of nucleotides within the inverted segment is flipped.
- Reverse Complement: Each nucleotide in the reversed segment is also changed to its complementary base (A becomes T, T becomes A, C becomes G, and G becomes C). This step is what differentiates an inversion from a simple reversal.
- Multiple Nucleotides Involved: By definition, a sequence inversion must involve two or more nucleotides. A single nucleotide change is simply a substitution.
- Comparison to a Reference: Inversions are identified by comparing the altered sequence to a known reference sequence.
Example
Let's say we have a reference DNA sequence:
5'-ATGCGT-3'
An inversion might result in the following altered sequence:
5'-ACGCAT-3'
In this case, the 'TGC' segment has been inverted and converted to its reverse complement 'GCA', giving the sequence 'ACGCAT'.
Significance
Sequence inversions can have several consequences:
- Altered Gene Expression: An inversion can disrupt gene expression by separating a gene from its regulatory elements, or by placing a gene under the control of a different regulatory element.
- Evolutionary Variation: Inversions can contribute to genetic diversity within a population.
- Genetic Disorders: In some cases, inversions can cause genetic disorders, particularly if they disrupt a gene or affect chromosome pairing during meiosis.
- Suppression of Recombination: Inversions can suppress recombination within the inverted region, which can help to maintain favorable combinations of genes.
