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.

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