common descent means the evolutionary in biology and how they have something linked with their common ancestors.
Explained in greater detail, each gene resides at a specific locus (location on a chromosome) in two copies, one copy of the gene inherited from each parent. The copies, however, are not necessarily the same. When the copies of a gene differ from each other, they are known as alleles.
For example: GGATACCTAGGTAAT
Insertion: GGAT<u>G</u>ACCTAGGTAAT
a nucleotide that was not present before is inserted into the original sequence
Substitution: <u>C</u>GATACCTAGGTAAT
the first nucleotide was substituted in for another (C for G)
Frameshift (basically a insertion or deletion, we'll try deletion here): GATACCTAGGTAAT
the first nucleotide was deleted, causing the reading frame to be shifted (instead of GGA as the first codon, we have GAT)
The answer your looking for is the insula. Hope this helps.
