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.

image result for describe the various types of gene mutationsghr.nlm.nih.gov

the types of mutations include: missense mutation: this type of mutation is a change in one dna base pair that results in the substitution of one amino acid for another in the protein made by a gene. nonsense mutation: a nonsense mutation is also a change in one dna base pair.

explanation: