Complex sentence: The majority of the genome within somatic cells of individals are heterozygous, however one parental copy of a region can sometimes be lost resulting in the region lacking differences at these polymorphic loci (SNPs) and therefore showing loss of heterozygosity (LOH).
Split into simpler sentences: The majority of the genome within somatic cells of individals are heterozygous. However, one parental copy of a region can sometimes be lost, resulting in the region lacking differences at these polymorphic loci (SNPs) and therefore showing loss of heterozygosity (LOH).