Final answer:
The copying and homology-directed repair in a CRISPR-mediated lethal suppression drive occurs in the germline cells of the parents during meiosis/gametogenesis. It ensures that all cells of the offspring carry the mutation, leading to a lethal phenotype when both chromosome copies are altered.
Step-by-step explanation:
In a CRISPR-mediated lethal suppression drive that is designed to be lethal when the altered gene is present in both copies of the chromosome, the homology-directed repair (HDR) and copying processes usually occur in the germline cells of the parents during meiosis/gametogenesis. The reason for this is that germline mutations are transmitted to offspring, affecting every cell in their body, including the somatic and future germline cells. Furthermore, these processes need to occur during meiosis to ensure the altered gene is present in the gametes, which will ultimately contribute to the formation of a zygote and result in every cell of the offspring carrying the mutation.
During meiosis I, homologous recombination can occur, in which homologous chromosomes pair and exchange non-sister chromatid segments, introducing genetic variation and ensuring that gametes carry a mix of maternal and paternal genes. Recombinant chromosomes that result from this process carry a new combination of alleles, providing a source of genetic diversity.
If a lethal suppression drive were to occur, it would need to be carefully timed to coincide with gametogenesis in order to be successfully passed down to the next generation and express the lethal phenotype when embryos carry two copies of the altered gene.