Practice question

CRISPR editing of diploid mammalian cells can affect zero, one or both alleles. When Cas9 induces double strand breaks independently repaired by non-homologous end joining, distinct indel signatures arise per allele. If one chromosome acquires a single base insertion causing frameshift and homologous chromosome acquires base deletion at same locus, alleles carry different mutations yet both disrupted. This state is termed biallelic heterozygous or compound heterozygous mutant, differing from homozygous where both alleles share identical alteration and monoallelic where only one allele mutated.