Fertlization

Fertilization is the process by which male and female gametes fuse to form a new diploid organism. In sexual reproduction, males produce sperm, which are motile gametes, and females produce ova, which are larger, non-motile gametes. Fertilization typically occurs when a sperm cell successfully penetrates an ovum. This fusion of genetic material from both parents results in a zygote, the first cell of a new individual.

The process involves several stages. First, sperm must reach the ovum. This often requires overcoming barriers, such as the protective layers surrounding the egg. Once a sperm makes contact, it releases enzymes that help to break down these outer layers. Following penetration, a series of events occurs to ensure that only one sperm fertilizes the ovum. This includes changes to the ovum's surface that prevent polyspermy, the fertilization by multiple sperm.

After the sperm nucleus fuses with the ovum nucleus, their chromosomes combine. This restores the diploid number of chromosomes, with half inherited from each parent. The resulting zygote then begins a series of mitotic cell divisions, known as cleavage, which leads to the formation of an embryo. Fertilization is a fundamental event in the life cycle of most sexually reproducing organisms, from plants and fungi to animals. The genetic diversity introduced through fertilization is a key driver of evolution.