Module 5

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

Module 5: Lesson 5 Assignment

Retrieve the copy of the Module 5: Lesson 5 Assignment that you saved to your computer earlier in this lesson. Complete Part 1. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.

Self-Check

To ensure your understanding, complete the following questions on nondisjunction and abnormal meiosis and then check your answers. Ask your teacher for clarification of any concepts.

Carefully study this illustration and then answer the questions that follow.

SC 1.

1. What has happened that is not normal? What is this process called?
   
   
2. Sketch a normal gamete that should arise from the mother cell.

SC 2. Name three genetic disorders that are the result of nondisjunction.

Use the flow chart showing the results of nondisjunction in meiosis I to answer question 3.

SC 3.

1. In which division has nondisjunction occurred?
   
   
2. Why is the egg cell shown abnormal?
   
   
3. If the cell with twenty-two chromosomes were to give rise to the egg, would the egg be abnormal? Explain.

SC 4. Zygotes having an abnormal number of chromosomes are usually described by the terms monosomy or trisomy. What do these terms mean?

Assume the eggs that could be produced from the division shown in question 3 are fertilized as illustrated.

SC 5. Label each illustrated situation as either trisomy or monosomy.

SC 6. Identify the syndrome produced by each of the abnormal sex chromosome combinations shown in the chart.

SC 7. Some individuals may have the combination of sex chromosomes XXXY. What is the sex of this person? Explain why.

Read

There is a dramatic increase in the incidences of nondisjunction in female gametes as a woman ages. For example, the chances of having a Down syndrome child at age 25 is 1:1500, by age 30 the risk is 1:910, and by the age of 45 it is 1:30. A specific cause for this is unknown.

As a woman ages, the oocytes have been suspended in prophase I for many years. The chances have increased that the apparatus to complete meiosis properly has deteriorated. New research also indicates that a woman’s womb can becomes less selective for genetically compromised embryos, making it more likely to carry an embryo with a genetic disorder to term.

Genetic Testing

Recall from your studies in Unit B the various technologies used to test a fetus for genetic problems. Three common procedures are amniocentesis, cordiocentesis, and chorionic villi sampling. Each differs in terms of when it can be done, which material it tests, and how quickly the answers come back. Each test is the same in terms of what is being looked for: an abnormal number of chromosomes.

Try This

TR 2. Research the following genetic testing technologies and complete a table like the following. Share your work with your fellow students in the discussion area.

Ethical Concerns

Science is very good at seeking knowledge. However, it is not the role of science or even scientists to decide what should be done with that knowledge. Instead, this role falls on the shoulders of society. What are some ethical concerns that can arise from prenatal genetic testing? What is the tension or debate that focuses on prenatal testing? Use the discussion board to share ideas with your fellow students or discuss your ideas with your teacher.

Some groups within society may object to prenatal tests because of the possible risks to the fetus. Prenatal testing can jeopardize the pregnancy, for example, by resulting in a miscarriage or by introducing infection. Furthermore, based on the results of the testing, parents may choose to terminate the pregnancy.

Stem cell research is another controversial issue. Some people and groups may have ethical concerns because of the certain death it causes to the blastocyst from which these cells may be taken.

Module 5: Lesson 5 Assignment

Retrieve the copy of the Module 5: Lesson 5 Assignment that you saved to your computer earlier in this lesson. Based on what you have read, the videos you have watched, and any research that you have done, complete Part 2. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.

Watch and Listen

There is controversy about stem cell research. For information on Canada’s guidelines for research, search the Internet using the terms “cbc + archives + Canada’s guidelines + stem cell research” and watch the news documentary.