Simple Explanation of Loss of Genetic Diversity, or "Loss of Heterozygosity"

“…Two partners in a human chromosome pair…often line up next to one another in parallel array, look each other over, compare their respective DNA sequences, and then swap genetic information. One frequent result is that a gene sequence present on one chromosome will now replace the corresponding sequence carried by its partner. Before this information transfer, two distinct versions of a gene may have resided on the two paired chromosomes; afterward, one of these versions is lost, being replaced by a duplicated version of the gene originally present on the other chromosome. The result is two identical copies of a gene in a cell that previously carried two dissimilar versions.” (p. 75)