Events in Sexual Reproduction > Fertilization (Syngamy)

The fusion of the germ-cells (male and female) to form a zygote is called fertilisation.

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The process in which male and female gametes fuse to form a diploid zygote is called fertilization. The actual union of the male and female gametes during fertilization is called syngamy.

Fertilization is the fusion of the germ-cells, male and female, to form a zygote. It may also be stated as the process in which male and female gametes fuse to form a diploid zygote.
The actual union of the male and female gametes during fertilization is called syngamy.

• The most vital event of sexual reproduction is the fusion of gametes.
• In this event, male and female gametes unite with each other and form a diploid cell called the zygote.
• The complete event is called fertilization, while the actual union of the two gametes is called syngamy.
• The terms fertilization and syngamy are frequently used interchangeably.
• Organisms like rotifers, honeybees, some lizards and birds (turkey) do not show syngamy, but in these organisms, the female gamete undergoes development to form a new organism without fertilization. This phenomenon is called parthenogenesis.

• In most aquatic organisms, syngamy occurs outside the body of the organism, that is, in the water medium.
• This type of gametic fusion is called external fertilization.
• It occurs in the majority of algae, bony fishes and amphibians.
• Organisms showing external fertilization exhibit great synchrony between the sexes.
• They release a large number of gametes into the surrounding water to enhance the chances of gametic fusion.
• A main disadvantage of external fertilization is that the offspring are extremely vulnerable to predators, threatening their survival.

• In the majority of plants such as bryophytes, pteridophytes, gymnosperms and angiosperms, and in higher animals such as cartilaginous fishes, reptiles, birds and mammals, gametic fusion takes place inside the body of the organism.
• This type of fertilization is called internal fertilization.
• In such organisms, the egg is formed inside the female body where it fuses with the male gamete.
• The male gamete is motile and has to reach the egg in order to fuse with it.
• Therefore, the number of male gametes is very large in comparison to the egg.
• In seed plants, however, the non-motile male gametes are carried to the female gamete by pollen tubes.

• Fertilization is the process of fusion of two dissimilar sexual reproductive units called gametes.
• In flowering plants, the female gametophyte or embryo sac is situated in the ovule, at a distance from the stigma.
• Therefore, to transport male gametes into the embryo sac, the pollen transferred to the stigma produces a pollen tube.

• Fertilization is the fusion of male and female gametes to form a diploid zygote; the actual union of the gametes is called syngamy.
• In some organisms (rotifers, honeybees, and turkeys), the female gamete develops into a new organism without fertilization, which is called parthenogenesis.
• External fertilization occurs outside the body in water (algae, bony fishes, amphibians); many gametes are released, but offspring are vulnerable to predators.
• Internal fertilization occurs inside the female body (bryophytes to angiosperms; reptiles, birds, mammals); motile male gametes are produced in large numbers.
• In flowering plants, the embryo sac lies inside the ovule, so pollen on the stigma forms a pollen tube to carry the male gametes to it.