Postgraduate Program in Genetics and Molecular Biology, Institute of Biosciences, Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
Postgraduate Program in Animal Biology, Institute of Biosciences, Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
Genome Biol Evol. 2022 May 3;14(5). doi: 10.1093/gbe/evac055.
"Junk DNA" is a popular yet controversial concept that states that organisms carry in their genomes DNA that has no positive impact on their fitness. Nonetheless, biochemical functions have been identified for an increasing fraction of DNA elements traditionally seen as "Junk DNA". These findings have been interpreted as fundamentally undermining the "Junk DNA" concept. Here, we reinforce previous arguments that this interpretation relies on an inadequate concept of biological function that does not consider the selected effect of a given genomic structure, which is central to the "Junk DNA" concept. Next, we suggest that another (though ignored) confounding factor is that the discussion about biological functions includes two different dimensions: a horizontal, ecological dimension that reflects how a given genomic element affects fitness in a specific time, and a vertical, temporal dimension that reflects how a given genomic element persisted along time. We suggest that "Junk DNA" should be used exclusively relative to the horizontal dimension, while for the vertical dimension, we propose a new term, "Spam DNA", that reflects the fact that a given genomic element may persist in the genome even if not selected for on their origin. Importantly, these concepts are complementary. An element can be both "Spam DNA" and "Junk DNA", and "Spam DNA" can also be recruited to perform evolved biological functions, as illustrated in processes of exaptation or constructive neutral evolution.
“垃圾 DNA”是一个流行但有争议的概念，它指出生物体的基因组中携带的 DNA 对其适应性没有积极影响。然而，传统上被视为“垃圾 DNA”的 DNA 元件的生化功能已被确定。这些发现被解释为从根本上破坏了“垃圾 DNA”的概念。在这里，我们重申了之前的论点，即这种解释依赖于一种不适当的生物功能概念，该概念没有考虑到给定基因组结构的选择效应，这是“垃圾 DNA”概念的核心。接下来，我们提出另一个（尽管被忽视了）混淆因素，即关于生物功能的讨论包括两个不同的维度：一个是水平的、生态的维度，反映了给定的基因组元素如何在特定时间影响适应性；另一个是垂直的、时间的维度，反映了给定的基因组元素如何随着时间的推移而持续存在。我们建议“垃圾 DNA”应专门相对于水平维度使用，而对于垂直维度，我们提出了一个新术语“Spam DNA”，反映了这样一个事实，即给定的基因组元素即使在起源时没有被选择，也可能在基因组中持续存在。重要的是，这些概念是互补的。一个元素既可以是“Spam DNA”，也可以是“垃圾 DNA”，而且“Spam DNA”也可以被招募来执行进化的生物功能，正如在适应或建设性中性进化的过程中所说明的那样。
