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Gamete refers to the individual haploid sex cell, i.e, the egg or the sperm. Zygote is a diploid cell formed when two gamete cells are joined by means of sexual reproduction.
Comparison chart
 | Gamete | Zygote |
|---|---|---|
| Ploidy | Haploid; n | Diploid; 2n |
| Definition | Is a cell that fuses with another cell during fertilization (conception) in organisms that reproduce sexually. Females produced a large gamete called an egg cell while males produce a tadpole-like gamete called a sperm cell. | Zygote is the diploid cell that results from the fertilization between an egg and a sperm. |
| Genetic material or Chromosomes | Haploid - Carries half of the genetic material necessary to form a complete organism. In other words - contain only one set of dissimilar chromosomes | Diploid – Carries the complete genetic material necessary to form a complete organism In other words - contain paired chromosomes |
| Etymology | Came from the Greek word “gametes” meaning “husband” and “gamete” meaning “wife.” | Came from the Greek word “zygotos” meaning “joined or yoked or to yoke. |
| Occurrence in plants | In short plants, male gamete is a motile antherozoid, which needs water as a medium in which to move, the female gamete is contained in the archegonium. In taller plants the male gamete is contained in microspore, female gamate is in megaspore. | The zygote is formed within a chamber called the archegonium. |
| Chromosome composition | Has one copy of all autosomes and 1 sex chromosome, either an X or a Y. | Have two copies of all autosomes. Sex chromosomes present can be either XX or XY. |
| Location | In males: testis. In females: ovary | Found only in females in the fallopian tube of the female reproductive system. |
| Cell cycle | Arrested | Undergoes rapid mitotic divisions. |
| Morphology | Sperm: tadpole like. Oocyte: large and spherical | Spherical |
| Motility | Sperm: motile. Oocyte: non-motile | Non motile |
| Gives rise to | Zygote | Fetus |
Formation and Development of Zygotes
Gamete refers to a haploid sex cell that is a sperm in males and egg (oocyte) in females. Zygote is the diploid cell that results from the fertilization between an egg and a sperm.
In mammals, the sperm (male gamete) fertilizes the egg (ovum, the female gamete) and the fertilized egg is called a zygote. The ovum, and therefore the zygote, is much larger than a normal cell. The zygote contains one set of chromosomes from each gamete; so it has all the genetic information encoded in it for development. However, the genes are not immediately activated to produce proteins. First, the zygote undergoes mitotic cell division several times. This is called cleavage, a process during which the zygote subdivides into many smaller cells. The over all size of the zygote itself does not change. Mammalian zygotes eventually develop into a blastocyst, after which they are more generally termed an embryo, and then a fetus.
This video takes the example of human reproduction to illustrate the process of fertilization and the development cycle of a zygote into a fetus:
Ploidy
Gametes are haploid in nature. A haploid cell has only one set of chromosomes; hence it only has half of the genetic material necessary to form a complete organism. Zygote is formed when gametes fuse and is hence diploid in nature. A diploid cell has paired chromosomes, and hence has the complete genetic material necessary to form a complete organism.
Zygote, the diploid (2N) cell that results from the fusion of two haploid (N) gametes
Chromosome composition
Gametes are formed by the process of meiosis and hence carry only one type of each chromosome.23 autosomes and either an X chromosome or a Y chromosome (23, X/Y). While oocyte can have only an X chromosome the sperm can carry either an X or a Y chromosome. Zygotes have two copies of all chromosomes. Sex chromosomes present can be either XX or XY (46, XX/XY). While an XX carrying zygote will form a female, an XY carrying zygote will give rise to a male.
Location
Sperms are formed in the testis, a part of male reproductive system. Oocytes are formed in the ovaries, a part of female reproductive system. Zygote is formed when the sperm and the egg fuse in the fallopian tube, a part of female reproductive system.
Cell Cycle
Oocyte is arrested at metaphase of the second meiotic division before fertilization. Mature sperms formed via meiosis do not undergo cell divisions. Zygote formed by the process of fertilization undergoes rapid mitotic divisions to form blastocyst and subsequently the fetus.
Morphology
The sperm is a tadpole-like structure that has a head, a mid section and a tail. They have very less cytoplasmic content. Oocyte is the largest human cell and is just visible to the naked eye. The cell consists of a large amount of cytoplasm and is spherical in shape.
Mobility
The ovum and zygote are not externally active and move passively moved by the fluid-flow in the oviduct .The sperm cells are externally active and mobile, using their tails to swim against the stream of fluid in the oviduct.
End Product
The gametes on fusion during fertilization give rise to the zygote. The zygote by undergoing mitosis forms the fetus which gives rise to the organism.
References
Haploid 
Mitosis 
DNA 
Allele 
Eukaryotic Cells 
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