Final answer:
RNA sequencing is advantageous over finding ORFs for estimating gene numbers because it captures only expressed genes and excludes non-transcribed potential ORFs, reflecting gene function and expression more accurately.
Step-by-step explanation:
The student's question touches upon the methods used to determine gene function and the number of genes in an organism's genome. A key advantage of RNA sequencing (RNA-seq) over finding open reading frames (ORFs) is that RNA-seq focuses on transcribed RNA, providing an accurate reflection of actively expressed genes. When researchers construct libraries using mRNA, they are able to capture only the expressed genes, which means potential ORFs that aren't transcribed are excluded.
This is important because ORFs might exist in the genome that are not actually functional genes; they are simply sequences that could, in theory, encode proteins. Determining function through reverse genetics and other techniques, such as RNAi silencing, can help attribute functions to these sequences by observing the effects of gene knockdown. Moreover, RNA-seq allows for the discovery of novel transcripts and alternative splicing events that could lead to different protein isoforms, highlighting the complexity and dynamic nature of genomes and underlining the significance of post-transcriptional modifications such as RNA splicing. Therefore, RNA-seq is a powerful tool for capturing the functional complexity of a genome beyond simple ORF identification.