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Did you know how environmental factors quietly affect the expression of our genes?
Many people’s understanding of genes often remains in a simple inheritance model, but in fact, the expression of many complex characteristics is affected by multiple genes and environmental factors. These complex traits are difficult to explain using Mendel's laws of inheritance, leading scientists to explore the subtle interactions between genes and the environment.
The existence of complex traits has forced the scientific community to re-evaluate traditional understandings of genetic inheritance, especially when explaining continuously changing traits.
Take human height as an example. This is a typical continuous trait, and many genes jointly affect the performance of height. Research points out that an estimated 50 genes are involved in the regulation of human height, and environmental factors such as nutritional intake are also related to this.
In addition to height, other complex traits include crop yields, plant color, and many diseases such as diabetes and Parkinson's disease. A core goal of modern genetics is to understand the molecular mechanisms of how these genetic variations contribute to complex traits.
Historical background
With the rediscovery of Mendel's work in 1900, there was a heated debate in the scientific community over whether Mendel's laws could be used to explain the observed continuous changes. Among them, scholars from the biometric school believe that most continuous traits such as height are hereditary, but cannot be explained by a single Mendelian genetic factor.
In 1919, the research of Leonard Fisher brought a turning point in this debate, when he showed that the additive contribution of multiple genetic factors to each trait can explain the variation of continuous traits. However, the number of genes involved in these traits remains unclear, and until recently many genetic variants were discovered, most of whose effects were not captured in GWAS (genome-wide association studies), leading us to rethink genetics. Complexity.
Types of complex features
Measurement characteristics
Measurable traits are traits that occur on a continuum and are affected by many genes with varying effect sizes. Taking height as an example, the heritability is estimated to be about 60-80%.
Integer features
The performance of integer features is described by integers. For example, a hen can lay one to five eggs per week, but not a few tenths of an egg. Such characteristics may also be influenced by the environment.
Threshold features
Threshold features have limited expressions (usually two). Such characteristics are commonly seen in medical contexts, such as the presence or absence of type 2 diabetes. Therefore, many diseases show this pattern.
Research methods of complex features
Twin study
By observing monozygotic twins (identical) and dizygotic (fraternal) twins, scientists can explore the influence of environment on complex traits. Because identical twins typically share 100% of their DNA, differences in performance between them come primarily from environmental factors.
QTL mapping
Many complex traits are determined by quantitative trait loci (QTL). Researchers select or filter out the characteristics of interest and then use genetic mapping to find relevant gene regions to explore all genes that may affect the characteristics.
GWAS
Genome-wide association studies (GWAS) are a technique used to discover genetic variants associated with complex traits. By randomly mating populations, researchers can test all genetic variants simultaneously and look for different SNP variants by comparing two populations with the presence or absence of the trait.
Understanding of genetic architecture
Genetic architecture is a comprehensive explanation of all genetic factors that influence complex traits. Recent studies have shown us that most of the gene loci identified by GWAS are actually within non-coding regions, suggesting that these variants may be mainly involved in gene regulation rather than directly changing protein sequence.
In exploring the functional consequences of these variants, many investigators have focused on key genes and pathways. However, some studies have proposed the "genome-wide hypothesis", which believes that although stray genes have a small impact, their collective impact may exceed that of core genes. As research deepens, we are increasingly aware that the interaction between environmental factors and genes is not a simple cause-and-effect relationship, but a complex dance.
Do environmental factors really subtly reshape our genetic expression and have a long-term impact on future health?
