A fruit fly has four chromosomes. The zygote formed by the sperm and the egg of fruit flies will have chromosomes.
If a fruit fly has four chromosomes then they would only pass on half of their chromosomes to the offspring. The new fly would have gotten 2 chromosomes from the father and 2 from the mother making it 4 chromosomes in total.
2 from the sperm & 2 from the egg so four chromosomes all together