Lewis/Life - Teaching Techniques

Chapter 14 - Teaching Techniques

A. General Tips
In general, your students will find this chapter to be quite interesting. Everyone likes to talk about inheritance, especially abnormal inheritance. Be prepared for some questions you may be unable to answer.
Chromosomes were biochemically identified in 1869 (published 1871) as nucleic acid. The relationship between DNA and genetics was not confirmed until 1944. Watson and Crick did not publish their delineation of the structure of the DNA molecule until 1953.
Some of the students may have heard about sex-influenced traits. Lewis does not cover this topic. Sex influenced traits are autosomal but are influenced by the sex chromosomes.
The classic example of a sex-influenced trait is male pattern baldness. The gene for this trait is not on either of the sex chromosomes, but the action of the sex chromosomes influences the expression of the trait. This could be termed a type of epistasis. Male pattern baldness is dominant in the male and recessive in the female. If you use this example, be certain the students realize that the gene for male pattern baldness does not code for complete baldness, nor is it the only cause of baldness.
Another example of a sex-influenced trait is the presence of horns in one type of sheep. Having horns is dominant in males but recessive in females. There is a great deal of history connected with the material in this chapter. Encourage your students if they are interested in delving into this history in order to better understand where we are today.
You might wish to copy and distribute to your students the Overview of Chapter Objectives flowchart found at the beginning of this Instructor's Manual Chapter.
B. Possible Approaches to the Chapter
You might begin this topic by asking the students to write down how long they think our shortest and longest chromosomes would be if they were stretched out and magnified to the size of a piece of videotape. Few will guess that the shortest would be 118 miles long and the longest would stretch for over 600 miles!
Relate Figure 14.2 to the previous chapters. If your students are shaky about meiosis, go through this process quickly with and without crossing over using Figure 14.2 as your reference point.
The Mastering Concepts questions in this chapter are especially good for students who have a weak background in this type of material. If you have such students, I suggest you assign these questions to be written out and handed in before you begin the class discussion.
If the students in your class have a fairly good understanding of basic genetics, require that they hand in (before you get to this topic) an annotated outline of the chapter. This type of assignment will firm up their understanding of the material while cutting to the core of what needs to be examined in more depth. This type of assignment also invites some rather interesting questions -- from the students.
Another idea for this material, particularly for classes with better backgrounds, is the assignment of a short paper on a concern specific to this chapter. Topics could include chromsomal abnormalities, sex-linkage problems, staining procedures, etc. For additional control on the assignment, you could make a list of specific topics. This assignment should not be a simple report; rather, the paper should include some sort of controversy and a statement of what should be done about the controversy. The paper should conclude with an explanation of why the student thinks the way (s)he does.
C. Hints Related to Specific Chapter Topics
- II.A. Relate the peas and flies linkages to the study of worms and flies in chapter 12.
  Some of your students will not instinctively understand the section on recombinant progeny. If you write out the symbols on page 287, state specifically what the dashes are for.
- III. Most students will find this entire section very interesting. If you have time, you might consider doing (or assigning the students to do) some additional research in this area, particularly with regard to non-mammalian species. Point out the turtle and the slipper limpet on page 291.
- III.B-D. Some of your students will understand in theory but will have a difficult time putting into practice the idea that the male cannot be a carrier for a sex-linked recessive gene. To demonstrate a possible difficulty, ask the students to write the answer to this question: A man has patches of alligator-like skin, a trait known to be carried on the Y chromosome. What are the chances his granddaughter will be a carrier of this condition?
  Notice the Punnett square insert in Figure 14.8. Students have a difficult time remembering to write out the entire chromosome and write the gene as a superscript. Many will also try to put a gene superscript on the Y chromosome, even after you re-explain why one cannot be included.
- V. Be certain you know how much of the technical jargon you expect your students to know.
- VI. Most of the students will find this entire section fascinating. Lewis does a good job of including some of the non-stereotypic (or little known) facts about some of the abnormalities. This section is also good for outside research, either for in class or extra credit points. If you assign any outside work, however, be certain your students use up-to-date resources. Today's knowledge of some of the conditions listed in this section is completely different than it was even 15 or 20 years ago and yet the students seem to have greater access to the older references.
- VI.B.2. XYY is sometimes called Jacobs syndrome. You can bring the scientific method in here and show how Jacobs did shoddy research by not checking the general population for the extra Y chromosome.
- VII. Most students will find this section very interesting. I suggest you check ahead to chapter 16, beginning with page 341. You may want to cross-reference or combine the material on mutations.