Gene ________ varies considerably within a genome,
reflecting differences in intron size and in the spacing
between genes.
A gene is a sequence of DNA nucleotides that encodes a protein. A genome of an organism includes all of its genes. Surprisingly, even the most complex genomes such as the human genome have few coding genes (about 27,000) and 3% of the genome is actually coding.
The sequences found in the DNA of the gene but not in the mature mRNA are known as introns. Because they are removed through the process of RNA splicing. Introns interrupt, or separate, the exon sequences. The mean intron length is 50 bp to 100 kb. Exons, in contrast, vary in size from about 50 bp to a few kilobases, unlike introns. The greater size variation observed in introns compared to exons reflects the fact that introns do not encode polypeptides and do not appear in mature mRNAs.
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