[Campbell Biology P.499] The human genome is estimated to contain approximately 21,300 genes... | Practice Question

The human genome is estimated to contain approximately 21,300 genes, yet human cells are known to produce many more different polypeptides. Which of the following processes are commonly recognized to account for this discrepancy? Select all that apply.

  • A: Increased rate of gene duplication events.
  • B: Extensive alternative splicing of pre-mRNA.
  • C: High frequency of somatic mutations in coding regions.
  • D: Various post-translational modifications of proteins.
  • E: Rapid evolution of new genes from noncoding DNA.

Explanation

The discrepancy between the relatively low number of genes and the much higher number of distinct polypeptides in human cells is primarily explained by two key processes: 1 Alternative splicing of pre-mRNA , where different combinations of exons are included in the mature mRNA, leading to multiple protein isoforms from a single gene. 2 Post-translational modifications , where proteins undergo various chemical modifications e.g., phosphorylation, glycosylation, cleavage after synthesis, further diversifying their structure and function.