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Difference Between Zygote and Foetus

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Last updated date: 17th Apr 2024
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What is Zygote and Foetus? An Introduction

Let's start with a real-life incident to illustrate the significance of the zygote and the foetus. Imagine a couple who have been trying to conceive a child. After successful fertilisation, the zygote begins its journey of development inside the mother's womb, eventually transforming into a foetus. Understanding the difference between these two stages is crucial in comprehending the various phases of human growth and development.


The journey of human life begins with the extraordinary moment of fertilisation, where an egg and sperm unite to form a zygote. The zygote represents the earliest stage of human development, a single-cell organism containing the complete genetic blueprint. As development progresses, the zygote transforms into a foetus, a stage characterised by the growth and maturation of organs and systems. 


The zygote and the foetus are distinct phases in the prenatal journey, each with its unique characteristics. In this article, we will study the difference between zygote and a foetus through explaining zygote and foetus.

Definition of Zygote and Foetus

Zygote: A zygote is a single-cell organism formed by the fusion of an egg cell and a sperm cell during fertilisation. It is the earliest developmental stage of a human being and contains the complete set of genetic information needed to form a new individual. 


Foetus: A foetus is the stage of prenatal development that follows the embryonic stage and extends from the ninth week after fertilisation until birth. During this period, the organs and systems of the body continue to grow and mature.


From Zygote to Foetus: A Journey of Miraculous Development

A zygote is an initial cell formed by the fusion of sperm and egg, marking the beginning of an individual's development. A foetus is the stage of prenatal development after the embryonic stage, characterised by rapid growth and organ formation.


Zygote:

  • After fertilisation, the zygote undergoes rapid cell division through a process called cleavage.

  • The zygote travels through the fallopian tube towards the uterus, where it implants into the uterine lining.

  • It is the only stage of human development where the genetic material comes from both parents.


Foetus:

  • By the end of the first trimester, the foetus has developed all major organs, and its gender can be determined.

  • The foetus can hear sounds from outside the womb, and studies have shown that it can respond to familiar voices and music.

  • During the third trimester, the foetus undergoes significant brain development and gains substantial weight.


Differentiate Between Zygote and Foetus

S.No

Characteristic

Zygote

Foetus


Stage

Early development

Prenatal development


Size

Single-cell

Multi-cellular organism


Potency

Totipotent

Differentiated


Cell Division

Rapid and continuous

Slower, focused on growth


Organs

Not yet developed

Developed and functioning


Vulnerability

Vulnerable to genetic 

abnormalities and miscarriage

Less vulnerable


Timeline

Up to 2 weeks post-fertilization

From 9 weeks post-fertilisation until birth


Mobility

Travels through the Fallopian 

tube towards the uterus 

Immobile,

located inside the uterus


Sensory Development

Not yet developed

Begins to develop,

responds to external stimuli


Gender

Not yet determined

Can be determined


Characteristics of Zygote and Foetus

A zygote is formed by the fusion of sperm and egg, initiating development. A fetus, in the later stages of pregnancy, undergoes rapid growth and organ formation, preparing for birth.


 Zygote:

  • The zygote is a single cell.

  • It is totipotent, meaning it has the potential to develop into any type of cell in the human body.

  • The zygote is primarily focused on rapid cell division and multiplication.

  • It is vulnerable to genetic abnormalities and miscarriage during early development.


Foetus:

  • The foetus is a multicellular organism.

  • It has already undergone significant cell differentiation and has distinct organs and systems.

  • The foetus grows in size and weight during this stage.

  • It is less vulnerable to genetic abnormalities and more likely to survive if born prematurely.


Summary 

The zygote represents the earliest stage of human development, starting from fertilisation and leading to the formation of the embryo. The foetus, on the other hand, is a later stage of prenatal development characterised by organ formation and growth. While the zygote is a single cell focused on rapid cell division, the foetus is a multicellular organism with developed organs and systems. Understanding the difference between a zygote and a foetus helps us appreciate the remarkable journey from conception to birth. So we were able to understand the Zygote and Foetus Difference in this article.

FAQs on Difference Between Zygote and Foetus

1. How Long does the Zygote Stage Last?

The zygote stage typically lasts for about two weeks after fertilisation. During this period, the zygote undergoes a rapid series of cell divisions through a process called cleavage. It begins as a single-celled entity and progresses into a cluster of cells known as a blastocyst. The blastocyst then travels through the fallopian tube towards the uterus, where it eventually implants into the uterine lining. The zygote carries the complete set of genetic information required for the development of a new individual, inherited from both the egg and the sperm.

2. At what Point does the Foetus Start Developing?

The fetus stage begins approximately nine weeks after fertilisation and continues until birth. By this time, the embryonic stage has passed, and the major organ systems have formed. The foetus undergoes significant growth and refinement throughout the remaining duration of the pregnancy. During this stage, external features, such as limbs, facial features, and sensory organs, become more distinct. The foetus also experiences further development of its central nervous system, skeletal system, and internal organs.

3. Can a Zygote Survive Outside the Womb?

No, a zygote cannot survive outside the womb. It requires the support and nourishment provided by the mother's body to continue developing into an embryo and subsequently a foetus. Once the zygote implants into the uterine lining, it establishes a connection with the mother's circulatory system through the placenta. The placenta facilitates the exchange of oxygen, nutrients, and waste products between the mother and the developing embryo/foetus. The womb provides the optimal environment with stable temperature, protection, and the necessary resources for the zygote's growth and development.