Difference Between QTL and GWAS

The key difference between QTL and GWAS relies on the type of sequences used in the analysis. QTL uses linkage gene loci to analyze phenotypic traits associated with polygenic inheritance while GWAS uses whole genome sequences to analyze single nucleotide polymorphisms of a particular condition.

QTL maps and GWAS play an important role in the genetic analyses for different traits. Furthermore, they are important in analyzing various disease conditions with unknown aetiology. In addition, sequencing plays a key role in both techniques. These techniques can further be coupled with other high throughput techniques for increased accuracy and precision.

CONTENTS

1. Overview and Key Difference
2. What is QTL 
3. What is GWAS
4. Similarities Between QTL and GWAS
5. Side by Side Comparison – QTL vs GWAS in Tabular Form
6. Summary

What is QTL?

QTL stands for Quantitative Trait Locus. It is a region of the DNA associated with a phenotypic trait. Generally, a QTL gives rise to polygenic effects. The distribution of QTLs varies, and the number of QTLs suggests the degree of variation of a particular phenotypic trait. Furthermore, they typically code for underlie continuous traits and not discrete traits.

Upon the identification of the QTL regions, it is important to sequence a particular QTL area. Moreover, to make investigations and research easy, sequencing and storing the sequence data of the common QTL regions take place with the involvement of bioinformatics. We call this technique QTL mapping. Subsequently, a database builds up with the QTL region sequences.

Furthermore, the applications of QTL sequences rely mainly on BLAST tool, where the sequence similarity can be determined. It is important in deducing relationships between organisms. Furthermore, it is important in determining the complexity of a particular polygenic phenotype. It also determines the evolution of a particular trait.

At present, QTL analysis is combined with other high throughput techniques like DNA microarrays. This is important in the expression analysis of the phenotype. Currently, scientists are much interested in developing the QTL database since QTL regions are responsible for many important traits of different species.

What is GWAS?

GWAS stands for Genome Wide Association Study. It also refers to whole genome association studies. These studies focus mainly on observational studies. It analyses the genetic variants of different individuals usually associated with a specific trait. Moreover, the whole genome is important for GWAS analysis.

GWAS is an important tool in the analysis of single nucleotide polymorphisms associated with various disease conditions. This is also a comparative study of the different single nucleotide polymorphisms across a wide population. In addition, the study sample of GWAS is very high; hence, it also takes the format of a cross-sectional cohort study.

Furthermore, the first GWAS study took place with regard to myocardial infarction and analyzing the genes associated with myocardial infarction. At present, GWAS plays an important role in determining the genetic background of complex diseases with unknown aetiology.

What are the Similarities Between QTL and GWAS?

• They rely on DNA sequences data for the analysis.
• Both are associated with the genetic backgrounds of various characters.
• Furthermore, they require bioinformatics tools to deduce and interpret results.
• They are done on large populations.

What is the Difference Between QTL and GWAS?

QTL analyzes the phenotypic traits associated with polygenic inheritance using linked gene loci while GWAS analyzes single nucleotide polymorphisms of a particular condition using whole genome sequences. Thus, this is the key difference between QTL and GWAS. QTL mapping is comparatively a less complex technique than GWAS since it requires whole genome sequencing.

The below infographic summarizes the difference between QTL and GWAS in tabular form.

Summary – QTL vs GWAS

QTL mapping and GWAS play a major role in determining the genetic background of various phenotypic traits. They also help in analyzing the genetic background of different diseases. QTL mapping maps the linkage genes responsible for continuous traits, and also involves mapping the polygenic inheritance genes. GWAS, on the other hand, takes place with whole genome analyzing for single nucleotide polymorphisms. In addition, this takes place across a larger population. Thus, this is the summary of the difference between QTL and GWAS.

Reference:

1. Liu, Ruixian, et al. “GWAS Analysis and QTL Identification of Fiber Quality Traits and Yield Components in Upland Cotton Using Enriched High-Density SNP Markers.” Frontiers in Plant Science, Frontiers Media S.A., 13 Sept. 2018, Available here.
2. “GWAS Vs. Qtl Mapping?” Latest Posts, Available here.

Image Courtesy:

1. “Example of a Genome-wide QTL-Scan from PLoS Biology” By – Styrkarsdottir U, Cazier JB, Kong A, Rolfsson O, Larsen H, et al. (2003) Linkage of Osteoporosis to Chromosome 20p12 and Association to BMP2. PLoS Biol 1(3): e69 (CC BY 2.5) via Commons Wikimedia
2. “GWAS Disease allele effects” By Bush WS and Moore JH – Bush WS, Moore JH (2012) Chapter 11: Genome-Wide Association Studies. PLoS Comput Biol 8(12): e1002822. doi:10.1371/journal.pcbi.1002822, (CC BY 2.5) via Commons Wikimedia