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

The number of predicted genes in an organism does not necessarily correlate with its genome size or the number of chromosomes because:

• Genome Size: The genome size includes both coding (genes) and non-coding DNA (introns, repetitive sequences, regulatory regions, and 'junk DNA'). Some organisms have large amounts of non-coding DNA which increases genome size without increasing the number of genes.
• Number of Chromosomes: The chromosome count indicates how DNA is organized, not how many genes are present. Different organisms can have varying numbers of chromosomes but similar gene counts.

Example: The pufferfish (Fugu rubripes) has a genome size of about 400 million base pairs, which is much smaller than the human genome (~3 billion base pairs), yet both have roughly a similar number of genes (~20,000). This is because the pufferfish genome has much less non-coding DNA.