Answer:
Meiosis
Step-by-step explanation:
Meiosis is one of the two types of divisions that cells usually undergo. However, meiosis is unique to sexually-reproducing organisms. Meiosis is the cell division which results in daughter cells with a reduced number of chromosomes (by half). Meiosis is used to produce gametes in sexually reproducing organisms.
According to the question, Labrador retriever contains 78 chromosomes in each of its muscle cells, which is a somatic cell. Since Labrador retrievers are sexually reproducing organisms, a male one will produce gametes (sperm cells) via the process of meiosis. At the end of the meiotic process, sperm cells with 39 chromosomes each will be produced.