The human genome contains approximately 10 6 copies of an Alu sequence, one of the best-studied classes of short interspersed elements (SINEs), per haploid genome. Individual Alu units share a 282-nucleotide consensus sequence followed by a 3'-adenine-rich tail region (Schmid, 1998). Given that there are approximately 3×109 base pairs per human haploid genome, about how many base pairs are spaced between each Alu sequence?

3000

Explanation:

- Human haploid genome >>> 3 x 10⁹ base pairs >>> 3,000,000,000 base pairs

- Human haploid genome >>> 10⁶ copies >>>  1,000,000 Alu Transposable Elements

- Space between each Alu Transposable Element (TE) >>>

3,000,000,000 base pairs / 1,000,000 Alu elements  = 3,000 base pairs

Alu elements are highly repetitive DNA sequences that account for approximately 20% of the human genome. These sequences (Alu) are considered to be non-autonomous Transposable Elements (TEs) capable of transposing within the genome via an RNA intermediary.