Zygote: Definition & Explanation Video

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  • 0:00 Definition of a Zygote
  • 0:18 Formation & Function
  • 2:24 Lesson Summary
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Lesson Transcript
Instructor: Derrick Arrington

Derrick has taught biology and chemistry at both the high school and college level. He has a master's degree in science education.

It is hard to believe that all life begins as one solitary cell. In this lesson, we will study zygotes. We will examine them closely to gain an understanding of how they are formed and their function.

Definition of a Zygote

Male sex cells are called sperm and female sex cells are called eggs. In order for reproduction to occur and new individuals to form, a sperm cell must unite with an egg cell. The resulting single cell formed is called a zygote.

The Formation and Function of a Zygote

In order for a new organism to form the process of fertilization must occur. This means that a sperm and egg cell must unite. A sperm cell carries half of the genetic information from the father organism. For this reason the sperm cell is considered to be haploid. The egg cell is haploid as well because it carries half of the genetic information from the mother organism. When the two halves combine they give the zygote a complete set of chromosomes and other genetic material from the parent organisms. Since the zygote contains a complete set of genetic information it is considered to be diploid.

A solitary sperm must enter an egg to form a zygote.
Photo of a sperm and egg.

This process of formation normally occurs during sexual reproduction. A zygote results when one sperm cell is able to penetrate the egg cell. During this time there are normally thousands of sperm competing for entry into the solitary egg. Once a single sperm penetrates the outer covering of the egg, a chemical change in the outer layer prevents any other sperm from breaking through. The sperm that entered then loses its tail, swells to form a nucleus, and unites with a similar nucleus formed by the egg. After the nucleus of the sperm has united with the nucleus of the egg, they combine their genetic information, giving the new single cell zygote a complete set of chromosomes.

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