Chapter 11 Lesson 2, "Chromosomes"

Materials:

• Chromosomes, (Workbook Activity)
• Modeling Sex Determination Lab sheet.

Objective:

• Students will explain what a chromosome is.
• Students will compare mitosis with miosis
• Students will explain how sex is determined in humans.
• Students will explain what a sex-linked trait is.

Anticipatory Set: *Show the students a series of pictures of a cell then slowly magnified until the students are looking at the double helx of a chromosome.

Discuss with the students the process of cell division as in earlier chapters and remind them that before a cell divides the DNA begins to come together and winds inself up very tightly until you can see its rod shaped structure called a chromosome.

Teacher Input: * Refresh the students memory of Mitosis and Meiosis using a scratch peice of paper and making a Venn Diagram with one side Mitosis and the other side Meiosis. Show the students a comparison of Mitosis vs. Meiosis. Then list the following characteristics and have the students put them in the correct location on the Venn Diagram.

• chromosomes duplicate
• one cell divides into two
• one cell divides into four
• Each cell produced has the same number of chromosomes.
• Each cell produced has half the number of chromosomes.
• asexual reproduction
• sexual reproduction
• cell division occurs twice.
• Original cell divides after chromosomes duplicate.
• Amoeba reproduction
• Human reproduction

If humans have 46 chromosomes in each cell, how many chromosomes would a human egg cell have? How many would a human sperm cell have? Show the students the picture from thier book on P273. Explain the picture.

Now show a picture of what most human chromosome sets look like. Note the last two chromosomes and what they look like. Point out that they are not the same size. Then show a picture of what the sex chromosome looks like. Explain that human females have both "X" type of chromosomes and that a male has an "X" and "Y" type. Discuss the punnett square on Page 275. Make one on a sheet of scratch paper and show how the chromosomes ar trasferred. What are the chances that an offspring will be male, female?

Next remind the students that the X and Y chromosomes are not the same length.(human chromosome sets) Does this have any effect on the traits that an individual has? Some of the information for a male is carried in only one place. If they have the recessive gene in that spot it always comes out. But for a female carrying the recessive gene in that location does not always show itself.

Explain that male baldness is a sex-linked trait. What does that mean? Show what the sex chromosome looks like again and discuss that baldness for a male is a recessive trait carried on the X chromosome in a location that is not on the Y chromosome. A female would only be bald if she carried the trait on both X chromosomes. If she carries the baldness trait on one she will not be bald. Show a Punnett scare and this time attach a B next to the X chromosome to stand for the baldness characteristic. Then ask this series of questions, What percent of the offspring will be male? female? What percent will be a female carrier of baldness but will not be bald? What percent of the offspring will be a male that will become bald? What percent will be male and not become bald?

Do the students know any other sex-linked traits. Thes are traits determined by an organism's sex chromosome, most of the time it comes from a gene on the X chromosome that is not on the Y chromosome this is an X-linked trait. Here is a short list of some:

• color blindness
• Hemophilia
• Muscular Dystrophy
• Hairy Ears, (A Y-linked trait)
• Frigile-X syndrome mental retardation
• hypotrichosis (less hair than normal)
• Ichthyosis (scaly skin)
• Lesch-Nyhan disorder (accumulation of uric acid and self-mutilative behavior)

Guided Practice: * Show the pictures of the diagrams on Page 277. Explain how the sex-linked trait of white eyes affects fruit flies.

Independent Practice: * Students will complete the worksheets, "Chromosomes" and "Modeling Sex Determination"

Check for Understanding: * Students will take a quiz on Lesson 2 Chromosomes.

Duration:

(2days) 30 minutes + 10-15 for Independent Practice (Could be longer if taken for homework).

Alaska Content Standards Addressed in this lesson:

• SCI A-9 Students will understand the transfers and transformations of matter and energy that link living things and their physical environment, fro molecules to ecosystems. (Flow of Matter and Energy)
• SCI A-10 Students will understand that living things are made up mostly of cells and that all life processes occur in Cells (Cells)
• SCI A-11 Students will understand that similar features are passed on by genes through reproduction (Heredity).
• SCI A-12 Students will distinguish the patterns of similarity and differences in the living world in order to understand the diversity of life and understand the theories that describe the importance of diversity for species and ecosystems.
• SCI A-13 Students will understand the theory of natural selection as an explanation for evidence of changes in life forms over time (Evolution and Natural Selection).
• SCI A-14 Students will understand
  • the interdependence between living things and their environments:,
  • that the living environments consists of individuals, populations, and communities: and
  • that a small change in a portion of an environment may affect the entire environment (Interdependence);

• SCI A-15 Students will use science to understand and describe the local environment (Local Knowledge); and:
• SCI B- 1 Students will use the processes of science; these processes include observing, classifying, measuring, interpreting data, inferring, communicating, controlling variables, developing models and theories, hypothesizing, predicting, and experimenting;
• SCI B- 2. Students will design and conduct scientific investigations using appropriate instruments
• SCI B- 3. Students will understand that scientific inquiry often involves different ways of thinking, curiosity, and the exploration of multiple paths.
• SCI B - 4. understand that personal integrity, skepticism, openness to new ideas, creativity, collaborative effort, and logical reasoning are all aspects of scientific inquiry.
• SCI B - 5. employ ethical standards, including unbiased data collection and factual reporting of results; and
• SCI B - 6. employ strict adherence to safety procedures in conducting scientific investigations.
• SCI C - 1. know how the words "fact," "observation," "concept," "principle," "law," and "theory" are generally used in the scientific community;
• SCI C -2. understand that scientific knowledge is validated by repeated specific experiments that conclude in similar results;
• SCI C- 3. understand that society, culture, history, and environment affect the development of scientific knowledge;
• SCI C- 6. understand that scientific discovery is often a combination of an accidental happening and observation by a knowledgeable person with an open mind;
• SCI C- 7. understand that major scientific breakthroughs may link large amounts of knowledge, build upon the contributions of many scientists, and cross different lines of study; and
• SCI C- 8. understand that acceptance of a new idea depends upon sup- porting evidence and that new ideas that conflict with beliefs or common sense are often resisted.
• SCI D- 1. apply scientific knowledge and skills to understand issues and everyday events;
• SCI D-2. understand that scientific innovations may affect our economy, safety, environment, health, and society and that these effects may be long or short term, positive or negative, and expected or unexpected;
• SCI D- 4. evaluate the scientific and social merits of solutions to everyday problems;
• SCI D- 5. participate in reasoned discussions of public policy related to scientific innovations and proposed technological solutions to problems; and
• SCI D- 6. act upon reasoned decisions and evaluate the effectiveness of the action.