DNA Double-Stranded Breaks (DSBs) are caused by genotoxic agents, such as ionizing radiation and chemical agents, and can cause an affected cell to undergo apoptosis or cell death. The process of microhomology-mediated end joining (MMEJ) shows promising results in the repair of DSBs in DNA. MMEJ is a mutagenic DSB repair mechanism that uses a certain length of homologous nucleotides adjacent to the DSB to align the broken DNA strands for repair. This can result in insertions, deletions, and even translocations of genes at the DSB site. This has led to discussions of debate on whether MMEJ is efficient in repairing DSBs in DNA. Based on the length of microhomology, the effectiveness of the DSB repair can vary. The purpose of this research is to examine MMEJ repair using micro-homologies of different lengths in Saccharomyces cerevisiae cells to test the effectiveness of MMEJ repair. The HIS3 gene located in chromosome 15 in the yeast cell is used to test for MMEJ repair, and the full microhomology length represents 311 base pairs (bp). Various crosses are performed on cells to attain desired genotypes that have the homologous chromosomes in alignment for MMEJ repair. After inducing DSBs, media-based testing is used for testing the efficiency of MMEj repair by checking for the presence of certain genes that may have formed or been deleted during the repair process.