"Heterozygous mutations" refers to when an organism carries two different versions of a gene, one normal and one mutated. This can lead to certain traits or conditions in the organism. Full definition
Compound heterozygous mutations in UBA5 causing early - onset epileptic encephalopathy in two sisters. (decode.com)
The new study shows that in AML, every possible combination of homozygous and heterozygous mutation occurs for the two gene mutations under study. (sciencedaily.com)
In Drosophila, we found that MCR mutations efficiently spread from their chromosome of origin to the homologous chromosome, thereby converting heterozygous mutations to homozygosity in the vast majority of somatic and germline cells. (science.sciencemag.org)