Final answer:
Sexual reproduction starts with gametogenesis and the production of haploid gametes by meiosis, followed by fertilization which creates a diploid zygote. This zygote undergoes mitosis to develop into a multicellular organism.
Step-by-step explanation:
Human sexual reproduction follows a specific order, beginning with the formation of gametes (sperm and eggs) in the gonads through a process called gametogenesis. This involves the production of haploid gametes by meiosis within the seminiferous tubules for sperm and in the ovaries for eggs.
Following gametogenesis, fertilization occurs when a sperm and egg unite, resulting in a diploid zygote with twice as many chromosomes, denoted as 2n. This restoration of the diploid condition ensures that offspring have the correct number of chromosomes. The zygote subsequently undergoes mitosis during early embryonic development leading to a multicellular organism.
The zygote inherits 2n chromosomes because it fuses genetic material from two haploid gametes, each contributing one set of chromosomes (n from each parent).