High school textbooks are aimed at high school students, and the definition of genes has limitations! Genetic effects of RNA virus RNA is also a gene. References:
In junior high school biology textbooks, genes are defined as "small units in chromosomal genetic material that determine biological characteristics". In high school biology textbooks, genes are defined as "DNA fragments with genetic effects". In the most authoritative Encyclopedia of China (2000 edition), a gene is defined as "a nucleotide sequence containing specific genetic information, which is the smallest functional unit of genetic information". In recent years, it has been published in foreign languages and some Chinese books on molecular biology and molecular genetics.
From the latest progress of the above-mentioned gene research, we can see that genes are not only multifunctional, but also structurally diverse. Therefore, it is quite difficult to give it a very accurate and always applicable definition. According to the current knowledge, from the perspective of molecular biology, a gene can be defined as "a nucleic acid sequence that can express a functional polypeptide chain or a functional RNA molecule". The "RNA molecule" here refers to rRNA and tRNA. "Nucleic acid sequence" mainly refers to DNA, and for RNA viruses, it refers to chromosomal RNA. This definition accurately expresses the essence and function of genes and is accepted by most scholars. So I think this definition can be understood by middle school students, especially high school students.