Login
Copyright

Polar Body: Definition, Formation & Twinning

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Cnidaria Respiratory System

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
 Replay
Your next lesson will play in 10 seconds
  • 0:00 What are Polar Bodies?
  • 0:23 How are Polar Bodies Formed?
  • 2:47 Polar Bodies and Twinning
  • 3:41 Lesson Summary
Add to Add to Add to

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Login or Sign up

Timeline
Autoplay
Autoplay
Create an account to start this course today
Try it free for 5 days!
Create An Account

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Shannon Compton

Shannon teaches Microbiology and has a Master's and a PhD in Biomedical Science. She also researches cancer and neurodegenerative diseases.

This lesson describes polar bodies. It answers two questions: what are they, and how do they form? It then describes how twins might arise because of polar body formation.

What Are Polar Bodies?

In the early 20th Century, scientists identified polar bodies for the first time. They were described as non-functioning egg cells because, with rare exception, they could not be fertilized. Instead, fusion with a polar body and a sperm typically caused the polar body to dissolve.

How Are Polar Bodies Formed?

So, how are polar bodies formed? Your DNA is stored in the nucleus of your cells as chromosomes. The DNA in each of your cells is a combination of your father's and your mother's DNA. Your parents' DNA was combined during fertilization, but if you think about this for a moment, you realize that your parents are a combination of their parents. They, in turn, are a combination of their parents. If you think about all the generations that led to you, you may start to wonder how all that DNA can fit inside each of your cells.

In truth, it doesn't. Your cells exist in a state called diploid. This means that each chromosome has a duplicate. We refer to these as chromosome pairs. One of the chromosomes in a pair comes from your father and the other from your mother. So, you actually inherit half of each parent's DNA.

How does this happen if your parents' cells are also diploid? How do their cells become haploid, having half the usual number of chromosomes? The secret lies in the way egg and sperm cells divide. Somatic cells, which are all the cells in your body except egg or sperm cells, undergo a type of cell division that makes two daughter cells that are diploid. This type of cell division is called mitosis. Egg and sperm undergo mitosis first, but then undergo a second type of cell division called meiosis. This is the type of cell division that results in haploid cells.

This type of cell division also results in polar bodies. When an immature egg cell, primary oocyte, undergoes its first division (mitosis) the daughter cells are diploid, so their DNA is equal. However, their cellular contents, cytoplasm, do not divide evenly. As a result, one cell is significantly smaller than the other. The smaller cell is called a primary polar body. The cell with most of cytoplasm is called a secondary oocyte.

Next, both cells undergo meiosis. The secondary oocyte undergoes uneven cell division. This produces a mature ovum, a mature egg cell, and another polar body. The primary polar body also undergoes meiosis and makes two secondary polar bodies. Usually, apoptosis will occur, which is a process in which all polar bodies die. This image shows how the sizes differ between oocytes and polar bodies.

Polar Body Formation
Image of cellular division

To unlock this lesson you must be a Study.com Member.
Create your account

Register for a free trial

Are you a student or a teacher?
I am a teacher
What is your educational goal?
 Back

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back

Earning College Credit

Did you know… We have over 95 college courses that prepare you to earn credit by exam that is accepted by over 2,000 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it free for 5 days!
Create An Account
Support