Difference Between Zygote and Fetus

Main Difference

The main difference between the zygote and fetus is that zygote is the initial stage of prenatal development which promotes the cell division while the fetus is the final stage of prenatal development which supports the development of organs.

Zygote vs. Fetus

A zygote is a fertilized egg formed after the fusion of male sperm with the female ovum while a fetus is a point in the zygote that shows all the functional organs of a mature organism. A zygote is unicellular on the other hand fetus is multicellular. A zygote is an initial stage in the development whereas a fetus is the last and final stage of prenatal development. Both zygote and fetus have diploid cells. A zygote is formed in the result of the fusion of male and female gametes while the fetus is formed from the zygote. A zygote is formed just after the fusion of gametes whereas a fetus is formed in the ninth week of development. In the case of the zygote, compaction and formation of blastula take place on the other hand in the fetal stage, functional organs are developed. A zygote is present in the fallopian tube while the fetus is present in the uterus.

Comparison Chart

ZygoteFetus
A zygote is that cell formed by the union of the ovum and sperm cellA fetus is a point in the zygote where it looks like a more human form
Number of Cells
Zygote is unicellularFetus is multicellular
Cell Type
Diploid cellDiploid cell
Formation
A zygote is formed by the fusion of male and female gametesA fetus is developed by the embryo
Period of Formation
A zygote is formed after the fusion of two gametesFetal period is from week nine until birth
Result Formation
Formation of blastula and compactionOrgan formation occurs
Location in the Body
A zygote is found in the fallopian tubeA fetus is located in the uterus

What is Zygote?

A zygote is a term used for the earliest stage of prenatal development. It is produced during sexual reproduction. It is also known as the first form of life. After the combination and karyogamy of the two haploid cells, a diploid zygote is formed. It contains the DNA from both parents. Then the zygote starts multiplying and develops into the embryo by the process of cell division. A zygote lasts for a week and then develops into the blastocyst and many other stages of development. After a few days of conception, zygote attached to the womb of the mother where it grows and develops. If we talk about the size of a zygote, a zygote consists of only one single cell and can only be seen by the use of a microscope. Increase in size and volume does not occur until a zygote turns in to an embryo. On this stage, there are no concrete, or visible developmental changes takes place except the division and reproduction of the original cells. Another phenomenon that takes place at this stage is the formation of twins or other multiples. Twins are formed when a zygote goes under the multiple divisions.

What is Fetus?

A fetus is that term which is used for the last developmental stage of an organism. The fetus stages come after the embryo stages in which the organism is entirely formed and ready to leave the womb. The fetal stage generally starts at the gestational age of eleven weeks and since the zygote is formed as the fetus is the last stage of development, so at this stage body organ and development are fully complete. Necessary organs and bones are already developed. Hair growth can be seen on the head and eyelashes on the eyelid. Fetal movements and swallowing also start inside the womb. One characteristic of the fetus is also that it reacts to environmental conditions like light and sound. The fetus is usually 30 millimeters and about 1.2 inches long. Fetus typically weighs around 8 grams. At this stage, the placenta is entirely functional, and genitalia starts to form. Hands, feet, brain and other organs are also present but with minimal functions. The fetal period lasts until the birth of the organism. In the case of humans, the fetal period lasts from week eight to weeks 38-40. Fingernails are also developed at this stage of development. Uncontrolled movements and twitches can be seen and feel due to the development of muscles and brain.

Key Differences

  1. A zygote is the very initial stage of development after fertilization while the fetal stage occurs at the eighth and ninth week of gestation.
  2. In the case of the zygote, the organism is still a cell that undergoes many different divisions, on the other hand, a young with a distinct body form and functional organs is known as the fetus.
  3. In the process of cleavage, the zygote can form the twins while a fetus always undergoes its internal changes and complete its last moments of growth.
  4. A zygote can be seen by the use of a microscope while a fetus can be seen from the ultrasound machine within the womb of the mother.
  5. A zygote is a unicellular organism while a fetus is multicellular.
  6. The location of the zygote is fallopian tube whereas the location of the fetus is the uterus.

Conclusion

The conclusion of this article is that zygote is a diploid, unicellular and the first stage of prenatal development located in the fallopian tube, on the other hand, a fetus is a diploid, multicellular, having functional organs and last stage of prenatal development.

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