Alterations to chromosomes are considered important in speciation (the process by which new species are formed). This is because several chromosomal rearrangements can make the genome of a few individuals in a population so different that they cannot successfully interbreed with the rest of the population. It is believed that, over time, this can lead to the evolution of two distinct species with different karyotypes (i.e. different sets of chromosomes making up the genome). In-depth testing of these ideas is now possible with advanced molecular technologies, which allow researchers to sequence DNA across entire genomes.