1. Module 5

1.16. Lesson 4

Lesson 4

Module 5—Cell Division: The Processes of Mitosis and Meiosis

Lesson 4—Meiosis

 

Get Focused

 

The photo shows identical plastic baby heads growing in plant pots.
© Elena Ray /shutterstock

 

identical twins: result of one egg fertilized by one sperm; occurs when the morula splits into two masses that develop independently in the uterus; offspring are genetically identical

Legend has it that everyone has a double—someone somewhere in the world looks just like you. Genetically, this is impossible unless you have an identical twin.

 

The reason for variation in individuals, meiosis, is the focus of this lesson. Unlike mitosis, where daughter cells are nearly identical, meiosis creates unique daughter cells called gametes by separating chromosome pairs. The average human male will create about 525 billion sperm (male gamete cells) over a lifetime, and not one will be the same genetically. In Unit B you learned that a sperm must fertilize an egg (female gamete cell) to create a new person. In this unit you will begin to understand the impossibility of there randomly being two individuals exactly alike. The creation of gamete cells is all about variation. This variation ensures the survival of a species, as you will discover later in Unit D.

The photo shows a man and a woman holding the woman’s very pregnant abdomen.

© Mikael Damkier/shutterstock

 

This lesson may take longer than 80 minutes to complete. You should devote the time necessary to ensure your understanding of meiosis.

 

In this lesson you will learn to describe the stages of meiosis, and you will come to understand when meiosis is necessary, as well as how it differs from mitosis. You will learn the major sources of genetic diversity, and why this is important to a species.

 

In this lesson you will examine the following focusing questions:

  • How does meiosis contribute to genetic variation?
  • What differences exist between identical and fraternal twins?

genetic variation: the permutations and combinations of genes and alleles possible; refers to different combinations of mother’s and father’s alleles in gametes; increases variation in the offspring and translates into better odds of offspring survival in changing environments

 

fraternal twins: two siblings born at the same time, resulting from the accidental ovulation of two eggs, which are fertilized by two sperm

 

Fraternal twins are as different as any two siblings.

 

 

 

 

 

 

 

 

 

 

 

 

 

Module 5: Lesson 4 Assignment

 

Download a copy of the Module 5: Lesson 4 Assignment to your computer now. You will receive further instructions on how to complete this assignment later in the lesson.

 

You must decide what to do with the questions that are not marked by the teacher.

 

Remember that these questions provide you with the practice and feedback that you need to successfully complete this course. You should respond to all of the questions and place those answers in your course folder.

 

Required Materials and Equipment

 

You will choose the materials you want to work with to create a cell model.