Miss Wilcox

Biology I

Natural Selection

Approximate time: 50 minutes

Objectives: TSW

1. Identify and illustrate how changes in DNA cause mutations and evaluate the significance of these changes. (5b)

Materials:

Whiteboard, markers, mutation and karyotype worksheet, textbook, colored pencils, paper, transparencies, vis-a-vis pens

Warm-up:

1.Define replication.

2.Define transcription.

3.Define translation.

Set: (review, objectives, involve, relevance)

Say, “On Friday, we reviewed the processes that must occur for proteins to be made correctly (DNA replication, transcription, and translation). But what happens when one of these processes goes wrong? Today, our aim is to identify and illustrate how changes in DNA cause mutations and to evaluate the significance of these changes. Right now, I would like you to look up the definition of mutation in your textbook and write it in your notes (1 min). (Mutations are mistakes in DNA sequencing/changes in DNA). By understanding the changes made on the genetic level, we can hope to understand the reasons behind genetic disorders or to trace the changes of organisms—their natural selection—over time.

Procedures:

1.Give general notes. Say, “Let's talk about mutations, changes in DNA. What causes mutation? Random error. Problems with machinery. Mutagens (external agents such as some types of radiation and some chemicals.) What is the nature of change? Change can be helpful, harmful, and sometimes neutral. What is a harmful result of mutation? Cancer. Carcinogens are mutagens linked to cancer (tobacco, asbestos, benzene). What is a helpful result? The expression of a trait that better suits an organism to an environment. Mutations that occur in an organism's body cells and affect the organism are somatic mutations. mutations that occur in an organism's germ cells (gametes), do not affect the organism, but can be passed on are germ-cell mutations. There are two broad categories of mutations: gene and chromosomal. Gene mutations change just one gene. Chromosomal mutations are when the structure or numbers of chromosomes change.”

2.Gene mutations: do sentence example. “The rat hid and the cat sat.” Illustrate substitution, insertion, and deletion and the affects. Ask students to make up own sentence of 3-lettered words and apply the same mutations. Have them put their results on the board.

3.Illustrate substitution, insertion, and deletion in a realistic example. “AAA UUU GGG CCC”.

4.Hand out worksheet. Tell students to complete first part. Then, have them exchange it with a partner.

5.Chromosomal mutations: show examples of duplication, deletion, inversion, and translocation. (Use transparency.)

6.Assign a different chromosomal mutation to each student and ask them to illustrate it.

7.Ask students, “How do geneticists identify chromosomal mutations? Karyotype (picture of an individual's chromosomes). They obtain a sample of cells, process them, and take a picture of the stained chromosomes during metaphase. The picture is enlarged, and the chromosomes are ordered and arranged for comparison.

8.Have students complete karytotype part of worksheet. Go over answers if time permits. Collect.

Closure: (restate, review, involve, preview)

Say, “ Today, we identified and illustrated how changes in DNA cause mutations and evaluate the significance of these changes. We used our knowledge about chromosomal mutations to evaluate a Smurfen karyotype for abnormalities. What is mutation? What types are there? What do they cause? Tomorrow, we will examine the technologies scientists use to learn about genetics.”

Assessment:

    Informal: TTW observe students working on the mutation examples.

    Formal: TTW grade students' worksheets for correct identification of gene and chromosomal mutations and record the grade in the grade book.