Final answer:
Fertilization achieves the important goals of restoring diploidy by merging haploid gametes to form a diploid zygote and generating genetic variability to enhance adaptability and survival. It is a key process in the sexual life cycle, preventing the doubling of chromosome numbers across generations.
Step-by-step explanation:
Fertilization is a crucial process in sexual reproduction, achieving several important goals for an organism. First and foremost, fertilization restores diploidy, combining two haploid gametes to form a diploid zygote, thereby maintaining the species-specific chromosome number. Contrary to a mistaken belief, fertilization does not merge two diploid cells into a haploid cell. In addition, fertilization generates genetic variability, which is a cornerstone of evolutionary adaptability and species survival. This variability arises from the recombinant nature of meiosis, which shuffles alleles before the gametes are formed. Not every fertilization event will result in a viable embryo, but when it does, it engenders a new organism with a unique genetic makeup.
As part of the sexual life cycle, specialized diploid germ cells undergo meiosis to produce haploid gametes. These gametes represent the only haploid stage in the life cycle of most animals. Successful fertilization then brings together these two disparate sets of chromosomes from the parents, reviving the diploid state essential for subsequent growth and development of the organism. Additionally, sexual reproduction necessitates a mechanism to prevent a continuous doubling of chromosome number across generations. This is ensured by meiosis—a nuclear division that reduces the chromosome count before gamete formation, preventing ploidy escalation in each generation.