- Structural variants are changes in the structure or organization of DNA that affect relatively large genomic segments compared with single-nucleotide polymorphisms (SNPs) and many small insertions or deletions (indels). They may involve the deletion, duplication, insertion, inversion, or movement of DNA segments within or between chromosomes. Structural variants contribute to genetic variation among animals and can influence gene function, gene regulation, inherited characteristics, and disease susceptibility. In animal breeding, understanding these variants helps researchers investigate genetic differences, identify important genomic changes, and improve genetic evaluation and selection strategies.
- Structural variants are commonly classified according to the type of DNA change involved. Deletions remove a segment of DNA, while duplications create additional copies of a genomic region. Insertions add DNA sequences at a particular location, and inversions occur when a DNA segment is reversed in orientation. Translocations involve the movement or exchange of DNA segments between different genomic locations, sometimes between chromosomes. Another important category is copy-number variation (CNV), in which individuals differ in the number of copies of a particular DNA region. These categories can overlap, and the classification of a variant depends on its genomic structure and the method used to detect it.
- The biological effects of structural variants depend on their size, location, and the genes or regulatory elements they affect. A deletion that removes an essential gene or part of it may disrupt normal biological function, whereas a duplication may change gene dosage and alter the amount of a gene product. Inversions can disrupt genes at their breakpoints or affect the inheritance of nearby genetic regions by changing recombination patterns. Structural changes may also affect regulatory sequences, influencing when, where, or how strongly genes are expressed. However, many structural variants have little or no measurable effect on an animal’s observable characteristics.
- In livestock populations, structural variants may contribute to differences in growth, body composition, coat colour, adaptation, fertility, disease resistance, and other economically or biologically important traits. Some variants have clear effects, while others influence traits only in particular genetic backgrounds or environmental conditions. Researchers investigate structural variants to understand the genetic basis of these characteristics and to identify variants that may be useful for breeding or health management. A statistical association between a structural variant and a trait does not automatically demonstrate causation, so functional evidence and validation in relevant populations are important.
- Structural variants can also be associated with inherited disorders. A deletion may remove essential genetic information, while a duplication or rearrangement can disrupt normal gene activity. Certain chromosomal rearrangements can affect fertility by interfering with chromosome pairing and segregation during reproduction, potentially producing unbalanced reproductive cells or reduced reproductive performance. Genetic testing may help identify relevant variants in affected animals or breeding populations, allowing breeders and veterinarians to make informed management decisions. Nevertheless, results must be interpreted according to the specific variant, inheritance pattern, and available evidence rather than assuming that every structural change is harmful.
- The detection of structural variants requires suitable molecular and genomic technologies. Whole-genome sequencing can identify many structural changes by examining DNA sequence reads and their alignment to a reference genome. Other methods include chromosomal microarrays, comparative genomic hybridization, and specialized sequencing approaches that can better characterize complex rearrangements. The accuracy of detection depends on the size and type of variant, sequencing coverage, genome quality, and the computational methods used. Repetitive DNA regions and complex genomic arrangements can be particularly challenging to analyse, making confirmation with an independent method valuable when results will influence important breeding decisions.
- Structural variants are increasingly studied alongside single-nucleotide polymorphisms (SNPs), insertions and deletions (indels), and other genetic markers. SNP arrays are highly useful for genomic selection and genetic relationship estimation, but they may not detect all structural changes directly, particularly those outside the regions covered by the array. Whole-genome sequencing and complementary analysis can provide a more comprehensive view of genomic variation. Combining different types of genetic information helps researchers investigate how DNA changes contribute to the genetic architecture of complex traits and inherited conditions.
- In animal breeding, structural variants may be incorporated into marker-assisted selection when a variant has a well-established relationship with a desirable trait or a harmful inherited condition. For complex traits such as milk production, growth rate, feed efficiency, fertility, and disease resistance, however, performance usually depends on many genes as well as environmental influences. A single structural variant rarely explains the full genetic basis of such traits. Genomic selection therefore generally relies on genome-wide information and statistical models that estimate an animal’s genetic merit using data from relevant reference populations. Structural variants may improve these models when they capture important genetic effects not adequately represented by other markers.
- The effects of structural variants should also be considered in relation to genetic diversity, genomic relatedness, and inbreeding management. Some structural variants are common and contribute to normal population variation, while others may be rare or associated with harmful effects. Monitoring relevant variants can help breeding programmes avoid undesirable genetic outcomes without unnecessarily removing valuable diversity from a population. Decisions should consider the frequency and impact of the variant, the availability of alternative breeding animals, and the long-term consequences of selection.
- Structural variants provide important information about the organization and function of animal genomes. Their study can reveal genetic mechanisms that are not fully captured by small DNA markers and can support research into inherited disease, reproduction, adaptation, and production traits. When combined with quantitative genetics, accurate phenotypic records, pedigree information, and reliable genomic analysis, structural-variant information can contribute to better breeding decisions. Their responsible use can support genetic improvement while maintaining animal health, welfare, and genetic diversity in sustainable livestock breeding programmes.
