Module 5 Cell Division

Reflect and Connect

Cell division and chromosome separation does not always follow the normal pattern. Nondisjunction events can lead to too many or too few chromosomes in gamete cells, which leads to individuals with serious conditions. Currently, science can conduct tests to analyze the chromosome counts of an unborn fetus, but there are no genetic treatments to reverse the problem of nondisjunction. After the process of fertilization involving a gamete with trisomy or monosomy, the resulting zygote will have too many or too few chromosomes, and each daughter cell from that zygote will also carry that error since mitosis will faithfully repeat the chromosome count to all of the body’s somatic cells.

Discuss

Stem cell research holds much promise for finding new treatments to many serious diseases. By starting with young, undifferentiated cells, scientists may be able to generate any number of missing or malfunctioning cells in adults. However, the collection of these cells destroys the blastocyst from which they are taken. From your reading of the text on p. 527, and from your review of the video on Canada’s guidelines for stem cell research, take a position on whether or not Canada’s guidelines give enough freedom to scientists while still respecting ethical concerns. Discuss your position with your classmates.

Lesson Summary

During this lesson you were to focus on the following questions:

• How do chromosome disorders occur and does their frequency increase with age?
• How can embryonic cells be used, and what tests may be done on an unborn fetus?

Chromosomes may not separate properly in meiosis I or meiosis II. This is known as nondisjunction. When this occurs in a gamete that is later fertilized and becomes a new individual, the result is a person with a serious condition, like Down syndrome for instance.

Tests like amniocentesis, cordiocentesis and CVS can diagnose the presence of abnormal chromosome numbers in an unborn fetus. However, no treatments can be done to change chromosome numbers since the error is found in every cell of that new life.

Early embryonic cells are totipotent. As a result, they can become any type of cell present in the human body. It is this characteristic that causes them to be of particular interest to scientists who are trying to find cures for diseases caused by adult cells shutting down or stopping regular function. Society will need to decide upon the guidelines which will be govern how scientists are allowed use these amazing cells.