Answer:
After attainment of puberty during the process of spermatogenesis.
Explanation:
Given that the fertilized egg has one X and one Y chromosome as the sex chromosomes, the zygote will develop into the human male.
After the attainment of puberty, the process of sperm formation, the spermatogenesis, would occur in the testes of the male.
Spermatogenesis includes meiosis in sperm mother cells to produce haploid sperms. During anaphase-I of meiosis I, the separation of homologous chromosomes to the opposite poles would separate the wild type allele Hbs from the allele for sickle cell disease, HbS.
The sperms produced by the end of meiosis II would have either HbS or Hbs allele.
