Related Experiment Video
Updated: Jul 18, 2026

10:17
An Allele-specific Gene Expression Assay to Test the Functional Basis of Genetic Associations
Published on: November 3, 2010
Major quantitative trait locus for eosinophil count is located on chromosome 2q
David M Evans1, Gu Zhu, David L Duffy
1Queensland Institute of Medical Research and Joint Genetics Program, University of Queensland, Brisbane, Australia. davide@well.ox.ac.uk
The Journal of Allergy and Clinical Immunology
|October 14, 2004
Summary
Researchers identified a quantitative trait loci (QTL) on chromosome 2q33 linked to blood eosinophil counts in adolescent twins, potentially revealing genes involved in asthma.
Area of Science:
- Genetics
- Immunology
- Pediatrics
Background:
- Eosinophils, a type of white blood cell, are linked to asthma and atopic diseases.
- Blood eosinophil levels in asthma patients correlate with symptom severity.
- Quantitative trait loci (QTL) analysis offers a powerful approach to map asthma-related genes.
Purpose of the Study:
- To pinpoint QTLs influencing eosinophil count variations in adolescents.
- To investigate genetic factors contributing to eosinophilia in twins.
Main Methods:
- Longitudinal measurement of eosinophil counts in 738 twin pairs at ages 12, 14, and 16.
- Genome-wide genotyping using 757 polymorphic microsatellite markers.
- Multipoint variance components linkage analysis to identify gene-trait associations.
Main Results:
- Highly significant linkage for eosinophil count found on chromosome 2q33 in 12-year-old twins (LOD=4.6).
- Suggestive linkage evidence in the same region for 14-year-olds (LOD=1.0).
- Additional suggestive linkages identified on chromosomes 2, 3, 4, 8, 9, 11, 12, 17, 20, and 22.
Conclusions:
- A specific QTL associated with eosinophil count is located on chromosome 2q33.
- This QTL may harbor genes crucial to asthma development and pathology.
Related Concept Videos
Pedigree Analysis
Overview
Epistasis
In addition to multiple alleles at the same locus influencing traits, numerous genes or alleles at different locations may interact and influence phenotypes in a phenomenon called epistasis. For example, rabbit fur can be black or brown depending on whether the animal is homozygous dominant or heterozygous at a TYRP1 locus. However, if the rabbit is also homozygous recessive at a locus on the tyrosinase gene (TYR), it will have an unshaded coat that appears white, regardless of its TYRP1...
X-linked Traits
In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.
X and Y Chromosomes
Among mammals, the gender of an organism is determined by the sex chromosomes. Humans have two sex chromosomes, X and Y. Every human diploid cell has 22 pairs of autosomes and one pair of sex chromosomes. A human female has two X chromosomes, while a male has one X chromosome and one Y chromosome.
The germline cells such as egg and sperm cells carry only half the number of chromosomes, i.e., 22 autosomes and one sex chromosome. All eggs have an X chromosome, while sperm cells can carry an X or...
The germline cells such as egg and sperm cells carry only half the number of chromosomes, i.e., 22 autosomes and one sex chromosome. All eggs have an X chromosome, while sperm cells can carry an X or...
X-linked Traits
In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.
Asthma I: Introduction
Asthma is a chronic inflammatory disorder of the airways characterized by variable airflow obstruction and heightened bronchial responsiveness to a wide range of triggers. The underlying inflammation leads to airway swelling, mucus hypersecretion, and smooth muscle constriction, all of which narrow the airway lumen and impede airflow. Clinically, asthma presents with recurrent episodes of wheezing, shortness of breath, chest tightness, and coughing, symptoms that typically vary in intensity and...

