Lesson 4 — Formation of Gametes


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?

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 has too many or too few chromosomes, and each daughter cell from that zygote carries that error because mitosis faithfully repeats the chromosome count to all the somatic cells of the body.

Proper chromosome separation is the foundation of the life cycle of an organism. If the correct number and assortment of chromosomes are not present in a gamete when it is fertilized, the resulting error is repeated throughout the entire organism when the fetus grows and develops by way of mitosis.

Tests such as amniocentesis, cordiocentesis, and chorionic villi sampling (CVS) can diagnose the presence of abnormal chromosome numbers in an unborn fetus. However, no treatments can be done to change chromosome numbers because the error occurs in every cell of that new life.

Unspecialized cells in a blastocyst have not yet entered a defined cell line or cycle. Early embryonic cells are totipotent (not specialized). As a result, they can become any type of cell present in the human body. This means they can be used to replace any damaged or ending cell lines in fully grown adults. This kind of research can extend life and increase the quality of life for many people, but it must be guided ethically by careful debate on the societal level.


Assignment

Complete the Lesson 4 set of questions in Assignment 5B and Assignment 5C