The human genome, whose sequencing was completed in the early 2000s, contains a surprisingly small number of genes (20-25,000).
What best explains the variation in the number of B and T cell receptors (more than a million combinations) found in white blood cells within an individual? A) Frequent transposable element transfer
B) High rates of crossover during prophase I
C) High levels of mutations within the genome
D) Differential intron removal and rejoining exons
D) Differential intron removal and rejoining exons
Explanation:
The human genome has only 20000-25000 genes which code for millions of proteins. Being eukaryotic organisms, human genes have introns, that is, the non-coding intervening sequences present between exons. Introns are removed by post-transcriptional splicing of RNA. Alternate splicing of introns and rejoining of exons give rise to different protein products from the same mRNA. This is how, a small number of human genes code for millions of protein products.
