An important characteristic of angiosperms is double fertilization, where two nuclei (of sperm) from each of the pollen tubes go on to fertilise two other cells that belong to the ovary. A diploid zygote is formed when one of the sperm cells fertilizes one of the egg cells. An embryo now develops from this diploid zygote. The fusion of the cells in such a scenario is called syngamy. It can be noted that syngamy is also referred to as true fusion and generative fertilisation.
Types of syngamy
Syngamy is of two kinds on the basis of the source of fusion gametes, which are
- Self-fertilization or Endogamy: The includes the fusion of two forms of gametes originating from the same parent for example, Taenia. It is a process is very uncommon.
- Cross-fertilization or Exogamy: When two fusing gametes for example in human, frog, cockroach, etc. are derived from separate parents. It is more general.
There are three types of syngamy and they are:
- Isogamy: This occurs when the gametes that fuse are similar. An advanced system of recognition is used so as to avoid self-fertilization. Surface proteins such as cells of immune system help in recognizing the different types of genotypes.
- Heterogamy: This happens when the gametes are of two different sizes. Based on the division of labor, the difference between the two gametes are done. Usually the female is larger while the male is smaller. Also, the number of male gametes is more so that there is an increase in the competition and makes fertilization likely.
- Oogamy: This takes place when the mobility of the gametes are different. Oocyte is the non-motile female and spermatozoon is the flagellate male. In most of the cases, spermatozoon is the only mobile gamete. Spermatozoa and spermatia are known as sperms.
Difference between Syngamy and Triple Fusion
|The fusion of male and female gametes during the fertilization is known as syngamy||The fusion of the sperm cell with the two polar nuclei during the double fertilization is known as triple fusion|
|During syngamy, zygote is produced which forms the embryo||During triple fusion, endosperm cells are produced which develops into endosperm|
|Diploid is the end result of syngamy||Triploid is the end result of triple fusion|
Below is the video explaining the double fertilization concept: