Difference Between Zygote and Foetus
The key difference between a zygote and a foetus is their developmental stage: a zygote is the initial cell formed after fertilization, while a foetus is a developing baby from around week 9 of pregnancy until birth.
The zygote’s formation marks the start of the human developmental journey, which continues to the foetus’s development. With their distinct traits and functions, these phases are essential to the emergence of life.
In this article, we will briefly discuss the difference between a zygote and a foetus, their key features, and their similarities and differences.
Table of Content
- What is the Difference Between Zygote and Foetus?
- What is Zygote?
- What is Foetus
- Key Similarities and Differences Between Zygote and Foetus
What is the Difference Between a Zygote and a Foetus?
| Parameter | Zygote | Foetus |
| Definition | Fertilized egg cell | Developing baby post-embryonic stage |
| Development Stage | First stage post-fertilization | Advanced stage, weeks 9 to birth |
| Size | Microscopic | Visible to the naked eye |
| Cell Division | Rapid initial division (cleavage) | Organized growth and differentiation |
| Structure | Single cell | Complex structure with organs |
| Duration | Few days | Several months |
| Dependency | Complete dependency on mother | Still dependent, but partially formed |
| Detectability | Not detectable by ultrasound | Detectable by ultrasound |
| Genetic Material | Combined DNA from both parents | Developing unique genetic expression |
| Viability | Not viable outside the womb | Increasing viability towards birth |
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What is a Zygote?
A zygote is the initial cell that forms when two gametes, such as an egg and a sperm, combine during fertilization. This single cell contains all the genetic information necessary to develop into a new organism.
As the zygote undergoes rapid cell division, it eventually develops into an embryo. The zygote is crucial for the beginning of the development of a new individual in sexual reproduction.
Key Features of Zygotes
- Single Cell: The zygote is a single, fertilized egg cell.
- Genetic Material: Contains combined DNA from both parents.
- Rapid Division: Undergoes rapid cell division known as cleavage.
- Short Duration: Exists for a brief period, typically a few days.
- Microscopic Size: Too small to be seen without a microscope.
- Initial Development: Marks the first stage of human development.
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What is the Foetus?
The foetus is the developing baby from the end of the embryonic stage (around week 9 of pregnancy) until birth. This stage is characterized by significant growth and organ development.
Key Features of the Foetus
- Complex Structure: Develops complex structures, including organs and systems.
- Detectable by Ultrasound: Can be seen and monitored via ultrasound.
- Organ Development: Organs begin to function and develop fully.
- Growth: Significant increase in size and weight over time.
- Movement: Begins to move within the womb.
- Viability: Increasing chances of survival outside the womb as development progresses.
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Key Similarities and Differences Between Zygote and Foetus
- Both are stages in human development.
- Both contain genetic material from both parents.
- Both are dependent on the mother for nourishment and growth.
- Zygote is the initial stage post-fertilization, while the foetus is a later stage post-embryonic development.
- Zygote is a single cell; the foetus is a complex organism.
- Zygote exists for a few days; the foetus develops over several months.
- Zygote is microscopic; the foetus is visible to the naked eye.
- Zygote is not detectable by ultrasound; the foetus is.
- Zygote is not viable outside the womb; the foetus has increasing viability as it develops.
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