14.1 Basic concepts in genetic epidemiology
3 min read•july 25, 2024
Genetic epidemiology explores how genes influence health and disease. It uses key concepts like , , and to understand the genetic basis of traits and conditions. principles guide our understanding of how genes are passed down through generations.
Genetic markers are crucial tools in epidemiological studies. They help identify disease-related genes and assess genetic risk factors. , the non-random association of alleles, plays a vital role in genetic association studies by improving efficiency and power in pinpointing disease-associated regions.
Fundamentals of Genetic Epidemiology
Key terms in genetic epidemiology
Top images from around the web for Key terms in genetic epidemiology
Chapter 14. Mendel and Heredity | Biology for Majors (openstax import) View original
Is this image relevant?
Frontiers | The differential view of genotype–phenotype relationships View original
Is this image relevant?
Dominant and Recessive Genes – Classroom Partners View original
Is this image relevant?
Chapter 14. Mendel and Heredity | Biology for Majors (openstax import) View original
Is this image relevant?
Frontiers | The differential view of genotype–phenotype relationships View original
Is this image relevant?
1 of 3
Top images from around the web for Key terms in genetic epidemiology
Chapter 14. Mendel and Heredity | Biology for Majors (openstax import) View original
Is this image relevant?
Frontiers | The differential view of genotype–phenotype relationships View original
Is this image relevant?
Dominant and Recessive Genes – Classroom Partners View original
Is this image relevant?
Chapter 14. Mendel and Heredity | Biology for Majors (openstax import) View original
Is this image relevant?
Frontiers | The differential view of genotype–phenotype relationships View original
Is this image relevant?
1 of 3
- Genotype defines genetic makeup of organism composed of alleles inherited from parents represented by letters (AA, Aa, aa)
- Phenotype describes observable characteristics or traits resulting from genotype and environmental interactions (eye color, height, disease status)
- Heritability measures proportion of phenotypic variation due to genetic factors ranging from 0 to 1 calculated using twin or family studies
- refers to alternative forms of a gene at specific can be dominant or recessive
- Locus pinpoints specific location of gene on chromosome
Principles of Mendelian inheritance
- Mendel's Laws
- states alleles separate during gamete formation each gamete receives one allele for each trait
- explains alleles for different traits assort independently applies to genes on different chromosomes
- Inheritance patterns
- requires one copy of mutant allele causes phenotype
- needs two copies of mutant allele for phenotype
- involves genes located on X chromosome
- predict offspring genotypes
- Relevance to genetic epidemiology
- Identifies inheritance patterns of diseases
- Allows risk assessment in families
- Guides genetic counseling and screening programs
Genetic Markers and Association Studies
Types of genetic markers
- (SNPs) represent single base pair variations in DNA sequence most common type of genetic variation used in genome-wide association studies (GWAS)
- consist of short tandem repeats of DNA sequences highly polymorphic used in linkage studies and forensics
- (CNVs) involve structural variations including deletions or duplications associated with complex diseases
- (RFLPs) show variations in DNA sequence recognized by restriction enzymes used in early genetic mapping studies
- Applications in epidemiological studies
- Identify disease susceptibility genes
- Assess genetic risk factors
- Study gene-environment interactions
- Conduct pharmacogenomics research
Concept of linkage disequilibrium
- Linkage disequilibrium (LD) describes non-random association of alleles at different loci measured by D' or r² statistics
- Factors affecting LD
- Recombination rate
- Population history (bottlenecks, admixture)
- Natural selection
- represent regions of high LD in genome allow for efficient genotyping strategies
- Importance in genetic association studies
- Enables use of capturing information about set of SNPs in high LD
- Improves power and efficiency of association studies
- Helps fine-mapping of disease-associated regions
- Limitations
- LD patterns vary across populations
- May lead to false-positive associations if not properly accounted for
Key Terms to Review (19)
Allele: An allele is a variant form of a gene that arises by mutation and is found at the same place on a chromosome as other variants of that gene. Alleles contribute to the diversity of traits within a population and can influence susceptibility to diseases, thereby linking genetics to health outcomes and interactions with environmental factors.
Autosomal dominant: Autosomal dominant refers to a pattern of inheritance in genetics where a single copy of a mutated gene located on one of the autosomes (non-sex chromosomes) is sufficient to cause a particular trait or disorder. This means that if one parent carries the mutated gene, there is a 50% chance that each child will inherit the condition, regardless of the sex of the child. This mode of inheritance is crucial in understanding how certain genetic disorders are passed down through generations.
Autosomal recessive: Autosomal recessive refers to a mode of inheritance where two copies of an abnormal gene must be present for the disease or trait to manifest. In this pattern, both parents must carry and pass on a copy of the mutated gene for their offspring to express the condition, even if they themselves are unaffected. This concept is crucial in understanding genetic disorders, especially when evaluating family histories and potential risks in populations.
Copy number variations: Copy number variations (CNVs) are a type of genetic variation where sections of the genome are repeated, leading to differences in the number of copies of particular genes among individuals. These variations can influence gene expression and play a crucial role in genetic diversity, disease susceptibility, and various traits across populations.
Genotype: Genotype refers to the genetic makeup of an individual, specifically the set of genes that an organism carries. It encompasses both the alleles inherited from parents and any mutations that may exist within those genes. Understanding genotypes is crucial for examining how genetic variations contribute to the development of diseases and how these variations interact with environmental factors.
Haplotype blocks: Haplotype blocks are contiguous stretches of DNA that are inherited together and can consist of one or more genetic variants. These blocks result from the process of linkage disequilibrium, where specific alleles at different loci on a chromosome are found together more often than would be expected by chance, allowing researchers to study genetic associations in populations more effectively.
Heritability: Heritability is a measure of how much of the variation in a trait within a population can be attributed to genetic differences among individuals. It provides insight into the extent to which genetics influence traits, helping to distinguish between inherited and environmental factors. Understanding heritability is essential for genetic epidemiology as it informs researchers about the potential for certain traits or diseases to run in families.
Law of independent assortment: The law of independent assortment states that alleles for different traits are distributed to gametes independently of one another during the formation of reproductive cells. This principle is fundamental in genetics, as it explains how different traits can be inherited separately and contributes to genetic variation within populations.
Law of segregation: The law of segregation is a fundamental principle of genetics stating that during the formation of gametes, the two alleles for a trait separate from each other, so that each gamete carries only one allele for each gene. This principle is crucial for understanding how traits are inherited and how genetic variation arises in populations, forming the basis for Mendelian inheritance patterns.
Linkage disequilibrium: Linkage disequilibrium refers to the non-random association of alleles at different loci in a population. It occurs when specific combinations of alleles or genetic markers are inherited together more often than would be expected under random assortment. This concept is crucial in genetic epidemiology as it helps to identify associations between genetic variations and diseases, making it easier to understand the genetic basis of complex traits and disorders.
Locus: A locus refers to the specific physical location of a gene or genetic marker on a chromosome. Understanding the locus is essential in genetic epidemiology because it helps researchers identify which genes may be associated with certain diseases or traits, as well as how genetic variations can impact health outcomes across populations.
Mendelian inheritance: Mendelian inheritance refers to the set of principles related to the transmission of genetic traits from parents to offspring, as first described by Gregor Mendel in the 19th century. This concept is foundational in genetics, establishing that genes come in pairs and are inherited as discrete units, influencing traits such as eye color and height. Understanding Mendelian inheritance is crucial for studying genetic variation and the hereditary patterns of diseases within populations.
Microsatellites: Microsatellites are short, repetitive sequences of DNA, typically 1 to 6 base pairs long, that are scattered throughout the genome. These variations in length among individuals make microsatellites highly polymorphic, allowing them to be powerful tools in genetic studies, including those examining population genetics and disease susceptibility.
Phenotype: A phenotype refers to the observable physical or biochemical characteristics of an organism, resulting from the interaction of its genetic makeup (genotype) with the environment. These traits can include everything from eye color and height to disease susceptibility and metabolic rates, highlighting the complex relationship between genetics and environmental influences in shaping individual characteristics.
Punnett Squares: Punnett squares are a visual tool used in genetics to predict the possible genotypes and phenotypes of offspring from a cross between two individuals. They help illustrate how alleles from parents combine and can show the probability of inheriting specific traits, making them essential for understanding inheritance patterns and genetic variation.
Restriction Fragment Length Polymorphisms: Restriction fragment length polymorphisms (RFLPs) are variations in the length of DNA fragments produced by the digestion of DNA with specific restriction enzymes. These variations arise due to differences in the DNA sequence among individuals, which can affect where the restriction enzymes cut the DNA. RFLPs are significant in genetic epidemiology as they help identify genetic diversity, track inheritance patterns, and associate specific genetic markers with diseases.
Single nucleotide polymorphisms: Single nucleotide polymorphisms (SNPs) are variations at a single position in a DNA sequence among individuals, which can influence traits, disease susceptibility, and responses to drugs. These tiny genetic changes are the most common type of genetic variation in humans and can serve as important markers in studying genetic diseases and traits across populations.
Tag SNPs: Tag SNPs, or tagging single nucleotide polymorphisms, are specific genetic variants that are used to represent a larger set of SNPs in a population. They help simplify the study of genetic variation by providing a way to capture the common genetic diversity without needing to analyze every single SNP individually. By identifying tag SNPs, researchers can efficiently link certain genetic markers to diseases or traits of interest, facilitating genome-wide association studies.
X-linked inheritance: X-linked inheritance refers to the pattern of genetic transmission of traits or disorders that are associated with genes located on the X chromosome. This form of inheritance often affects males more severely than females because males have only one X chromosome, while females have two, providing a potential backup if one X carries a mutation.