Question

With a suitable example, explain briefly, why the number of predicted genes do not correlate with the genome size and the number of chromosomes in an organism.

Hint:

Genome size and chromosome number do not directly reflect gene count due to non-coding DNA and chromosome organization differences.

Answer 1

Gene prediction counts in an organism are not directly proportional to its genome size or chromosome number for the following reasons:

• Genome Size: A genome comprises both coding regions (genes) and non-coding DNA. Non-coding DNA includes introns, repetitive elements, regulatory sequences, and other non-gene material. Organisms may possess substantial non-coding DNA, leading to a larger genome size without a corresponding increase in gene quantity.
• Chromosome Number: The number of chromosomes reflects the structural organization of DNA, not the gene content. Organisms can exhibit different chromosome counts while maintaining similar gene numbers.

Illustration: The pufferfish (Fugu rubripes) possesses a genome of approximately 400 million base pairs, considerably smaller than the human genome (approximately 3 billion base pairs). Despite this difference, both organisms contain roughly 20,000 genes. This is attributable to the pufferfish genome containing significantly less non-coding DNA.