Final answer:
To prevent a new organism from having twice as many chromosomes as its parents, the egg and sperm, which are haploid, contribute one set of chromosomes each to form a diploid zygote. Mechanisms like the prevention of polyspermy ensure only one sperm fertilizes the egg.
Step-by-step explanation:
During fertilization, an egg and sperm fuse to form a zygote. To prevent the new organism from having twice as many chromosomes as its parents, multiple protective mechanisms are deployed. First, when the initial sperm penetrates the egg, it causes the egg to complete its second meiotic division, resulting in the expulsion of a second polar body, effectively reducing its chromosome number.
Furthermore, the sperm and egg are each haploid, meaning they carry only half the usual number of chromosomes found in body cells. They each contribute one set of chromosomes to the newly formed zygote, creating a diploid cell with a full complement of genetic material. To safeguard this process, mechanisms such as the prevention of polyspermy exist, ensuring that only one sperm fertilizes the egg, thereby avoiding the formation of a triploid organism, which would be incompatible with life.
The zygote contains all the necessary genetic instructions needed to develop into a human. It represents the successful combination of genetic material from both parents, resulting in the formation of a new, genetically distinct individual.