Genes are DNA chains that encode proteins and play a key role in determining phenotype. Although some scholars emphasize the influence of the environment, from an evolutionary biology perspective, genes are still the key to phenotype determination. The environment can influence gene expression, but without genes, there can be no phenotype. Furthermore, through various genetic interactions, genes play a crucial role in shaping phenotypes.
We use the term “gene” in biology very often in everyday life. For example, there are countless expressions that refer to genes, such as the gene for height, the gene for studying well, the gene for obesity, and so on. Despite all these references, few people have a clear understanding of what a gene is, how it affects phenotypes, and whether it is the only source of information. Let’s take a closer look at genes from the perspective of evolutionary biology.
When asked the question, “What is a gene?”, few biologists can explain it simply and clearly. From a molecular biology perspective, a gene is a chain of DNA that encodes a protein. However, the genes we usually talk about represent only a small fraction of the total DNA chain. If we adopt the molecular concept, only exons and regulatory regions are genes. Different scientists define genes in different ways, but it’s easy to understand them in terms of evolution. For example, the eyeless gene in fruit flies drives the development of eyes during development. If the eyeless gene is not expressed, the fruit fly is born without eyes, showing that genes have a decisive effect on phenotype. In this way, a chain of DNA that affects a phenotype can be called a gene.
Now you know that genes are DNA chains that encode proteins. Genes determine phenotype by controlling the type of protein and when it is expressed. But how much of a role genes play in determining phenotype is debated. There are two schools of thought: genetic selection, in which genes play a dominant role, and multilevel selection, in which genes and the environment play equal roles. I believe in genetic selection, which is the mainstream view of evolutionary biology and hasn’t been challenged in over 100 years, and I want to emphasize the strong role of genes.
Some scholars question the idea that genes determine phenotypes. They argue that genes interact with the environment to shape phenotypes, where “environment” includes not only the ecological environment of the individual but also the molecular environment inside the cell. In other words, genes do not play a dominant role, but both genes and the environment have a strong influence on phenotypes. This is based on the fact that identical twins can have the same genes and still have different phenotypes depending on their environment. However, this argument can be resolved by defining genes in terms of evolution. Even if a gene is expressed in an optimized environment, the absence of the gene does not result in the phenotype. In other words, genes play a crucial role in determining phenotypes.
If genes determine phenotype, what is the relationship between genes and phenotype? In his research, Professor Richard Charles Lewontin distinguished four different ways in which phenotypes change in response to genetic or environmental changes: Genetic Determinism, Environmental Determinism, Epistatic Interaction, and Non-Epistatic Interaction. Genetic determinism refers to the same phenotype in any environment, while environmental determinism is the theory that different genes produce the same phenotype in the same environment. However, both theories have been proven false in today’s biology because they completely exclude the influence of genes or environment. Therefore, they don’t need to be mentioned anymore. Today, most biologists agree that both genes and the environment influence phenotypes. However, there is disagreement about which plays a more dominant role.
In a additive interaction, different genes produce different phenotypes in different environments, and these differences are maintained. A non-legal interaction means that the phenotypes of two genes can be reversed depending on the environment. Lewontin argues that most people only consider the latter, but in reality, the former is dominant. For example, the variation in height of milfoil with elevation or the variation in G1 survival with temperature during development in fruit flies. However, based on the research to date, it is difficult to conclude that non-legal interactions are dominant in the real world. Even if statutory interactions are more common, this does not mean that the influence of the environment is ignored in phenotype determination; phenotypes are still strongly influenced by genes.
Some scholars argue that genes do not have a unique influence in determining phenotype, citing the fact that genetic information does not reside solely in the DNA chain. For example, in maternal inheritance effects, genetic information does not reside solely in DNA, as maternal proteins or ribosomes contained in the egg influence early development. In addition, gene expression is regulated by the degree of acetylation of histone proteins, which are also partially inherited. The methylation of DNA itself also regulates gene expression, and this methylation information is passed on to daughter cells during cell division.
However, these examples do not support the claim that genes do not play a unique role in phenotype determination because the genetic information is not solely in DNA. Even if there is an environment that optimizes gene expression during an organism’s development, the absence of a gene does not result in a phenotype. Rather, the fact that there are different levels of genetic information suggests that interactions between genes are very important. For example, the vertebrate Pax6 gene and the fruit fly eyeless gene play the same role, so injecting the fruit fly eyeless gene into mouse embryos results in normal eye development. In this way, the interactions between genes are crucial in development.
Some scientists who are wary of genetic universalism do not accept that genes play a dominant role in determining phenotypes. They argue that a new research perspective is needed that takes into account the influence of the environment. However, we believe that gene-centered biology has unlimited scope for future research, and that the current paradigm has not yet experienced a major crisis.
