Chapter 11, Problem 7P

Mutations at simple sequence repeat (SSR) loci occur at a frequency of 1 × 10 per locus per gamete, which is much higher than the rate of base substitutions at SNP loci (whose frequency is about 1 × 10 per nucleotide pair per gamete).

a.	What is the nature of SSR polymorphisms?
b.	By what mechanism are these SSR polymorphisms likely generated?
c.	Copy number variants (CNVs) also mutate at a relatively high frequency. Do these mutations occur by the same or a different mechanism than that generating SSRs?
d.	The SSR mutation rate is much higher than the mutation rate for new SNPs. Why then have geneticists recorded more than 50 million SNP loci but only about 100,000 SSR loci in human genomes?