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Terry and Harrison, GENA Workshop 2009 Meiosis and Genetic Variation Introduction This lesson, Meiosis and Genetic Variation, is designed for first year high school biology students. It will be included in an introductory course in which the students have limited knowledge of classical Mendelian inheritance patterns. Students will learn how genetic information flows from one generation to the next via meiosis and fertilization. This exercise will focus on how independent assortment of chromosomes during meiosis contributes to genetic variation amongst siblings. Human cells have 46 total chromosomes; two each of chromosomes 1 to 22 and then either two X chromosomes (in females) or an X and a Y chromosome (in males). Gametes (sperm cells and eggs) have 23 chromosomes; one copy of chromosomes 1 to 22 and then either an X chromosome (in eggs) or an X chromosomes or a Y chromosome (in sperm cells.) Meiosis is the cellular process in which one cell (with 46 chromosomes) undergoes DNA replication and two successive cell divisions to end up with 4 haploid cells (gametes). When a sperm fertilizes an egg cell, each of the gametes contributes 23 chromosomes to the new embryo resulting in 46 total chromosomes (23 homologous pairs). In this way, we receive half of our chromosomes from our mom and the other half from our dad. As a cell undergoes meiosis, the total number of chromosomes in the resulting cells is reduced by half. As a result, our parents have passed on half of their chromosomes to each child. Which one of each of pair is passed on is due to random during meiosis. Students’ Misconception to Be Addressed in This Lesson Students learn about meiosis, but are often unable to understand how this leads to genetic variation, especially within their own family where they might look somewhat different from their siblings, even though they have the same parents. Georgia State Standard Addressed in the Lesson SB2. Students will analyze how biological traits are passed on to successive generations. SB2c. Using Mendel’s laws, explain the role of meiosis in reproductive variability. 1 Terry and Harrison, GENA Workshop 2009 Major Science Concept Addressed Independent assortment and crossing over during meiosis, as well as random fertilization of gametes, result in genetic diversity. Objectives of the lesson--------Students will learn 1. the role meiosis plays in passing traits from parent to offspring. 2. how sexual reproduction creates unique gene combinations. 3. why siblings do not look identical to one another despite having the same parents. Prerequisite skills that students will bring to the lesson 1. (Working) knowledge of the following genetics vocabulary: gene Punnett square allele monohybrid cross homozygous testcross heterozygous dihybrid cross genome law of independent assortment genotype probability phenotype crossing over dominant genetic linkage recessive 2. Differentiate between haploid and diploid cells. 3. Define the term homologous chromosome and identify the associated chromatids. NOTE: Although this might seem like we expect students to have a lot of prerequisite knowledge, this lesson plan will be done at the end of a unit on genetics. Therefore students will have already learned these terms in their biology class. Demographics of Students in the Classroom This is an inner city school comprised of 95% African-American students. The majority of the students come from a single-parent household and receives either free or reduced lunch. Our school is currently on the state’s “Needs Improvement” list (in accordance with Federal Mandate of “No Child Left Behind”). The class is comprised of 15 students 5 boys and 10 girls all African-Americans. All of the students express a high interest in the experimentation aspect of science. 2 Terry and Harrison, GENA Workshop 2009 Timeline of the Lesson- 3 class periods of 55 minutes Day 1 – Compare and contrast traits in related individuals A week (7 days) prior to introducing meiosis students are assigned to create a poster with pictures of immediate family members (Dad, Mom, siblings as well as grandparents to answer the question “Do You Have Dominant or Recessive Genes?” (See attachment #2) 1. Amy Harrison administered pretest. See attachment #1 entitled Chapter 6 “Process of Meiosis”. The class average on the pretest was 44%. 2. Engagement and Exploration: Students came to class having completed a preparatory assignment where they have created a poster with pictures of parents and siblings (see attachment #1). The posters were displayed randomly around classroom. Students dispersed throughout the room to view each poster and try to identify distinguishing characteristics of their classmates and determine which poster displays which classmates’ family. The class reassembled and report to the class what they have discovered (Posters will be held up individually as students report their findings) Day 2 - Explanation Dr. Christine Terry visited the classroom and went over the steps of meiosis. She explained what takes place in each step and how to apply Mendel’s law of independent assortment. She tried to gauge students’ understanding of the process by covering up the final steps in meiosis II and asking students to explain what the end products of meiosis will look like, given different arrangements of chromosomes during metaphase of meiosis I. She then described the process of crossing over between each pair of homologous chromosomes and showed students how the chromosomes would appear at the end of meiosis I and meiosis II. Although the following was included as part of our original lesson plan, we did not have time for this step given the constraints of a 55 minute period: Each student will draw a cell with four chromosomes going through meiosis (starting with prophase I and show crossing over between each pair of homologous chromosomes). Students should make note of how their cell looks at the end of meiosis I and meiosis II. (Students may use figure 6.5 pages 174-175 in McDougal Littell Biology for reference). 3 Terry and Harrison, GENA Workshop 2009 Day 3 – Investigating Genetic Variation Dr. Terry returned to the classroom and helped the students to complete the hands-on activity: “Investigating Genetic Variation” (attachment #3). By the end of the period, each pair of students had used the paper chromosomes to model meiosis and fertilization in order to create a single offspring from the same set of parents. As all offspring were produced by the same set of “parents,” students could see the similarities and differences of traits amongst the siblings were due to both (1) how homologous chromosomes aligned themselves during metaphase of meiosis I and (2) random fertilization of gametes. Day 4 – Assessment Students completed a post-test, which was composed of the same questions as the pretest (from Day 1). The class average on the post-test was 75% (compared to the class average of 44% on the pre-test). 4 Terry and Harrison, GENA Workshop 2009 Attachment #1 Pre-test/Post-test NOTE: This will be uploaded separately. 5 Terry and Harrison, GENA Workshop 2009 Attachment # 2 Chapter 6 Meiosis and Genetic Variation Overview Students will make observations of genetic variations within families and humans. Some examples of genetic variations includes: eye, nose, lip, ear, hair, face, and chin Prepare Students will bring to class unlabeled photographs of grandparents, parents and siblings on a poster board. (Students who are adopted may bring in photos of a famous family for display). Students will display the posters randomly around the classroom. Ask students to view the photographs and try to match the name of their fellow students with the photographs of their family members. After the students have determined who the photographs looks most like, show each poster individually and ask the students to verify their relatives and stand next to their poster. Ask the students to identify what are the similarities and differences in the features among family members. Purpose Explain how independent assortment during meiosis increases genetic diversity. 6 Terry and Harrison, GENA Workshop 2009 Attachment #3 Investigating Genetic Variation This activity has been modified from: “The Genetics of Parenthood” created by Lenore Kop and Thomas Crowley “Reebops” developed by Patti Soderberg. Before the Exercise: Prepare the chromosomes: Before carrying out this activity, the instructor will need to construct Mom’s and Dad’s chromosomes for each set of students. Each parent will have eight homologous chromosome pairs, or sixteen total chromosomes. Each “chromosome” will be double sided. One side will show the gray-scale images of chromosomes that are included at the end of this handout. The other side will be either pink or blue paper and will be labeled with the appropriate allele. 1. You will need to make four photocopies of Figure 1 for each group of students. 2. Glue two of these copies to pink construction paper. Cut the sixteen chromosomes apart along the lines provided. 3. Match up the homologous pairs and label the backs of the chromosomes with the appropriate allele (as shown in Figure 2). We have set up this activity so that the parents are heterozygous for the genes on chromosomes 1-7. The eighth pair of chromosomes is meant to represent the sex chromosomes and should be labeled as shown in Figure 2. 4. Glue the other two copies of Figure 1 to blue construction paper and cut the sixteen chromosomes apart along the lines provided. Repeat steps 4 and 5 for these chromosomes. 5. Note: These chromosomes can be laminated so they can easily be used over and over again in future classes. Put the chromosomes into envelopes: Obtain two envelopes for each set of students. Label one as “dad” and the other as “mom”. Place the sixteen “pink” chromosomes in the “mom” envelope and the 16 “blue” chromosomes in the “dad” envelope. 7 Terry aand Harrisonn, GENA Woorkshop 20009 Figure 1: The Parents' Chroomosomes 8 Terry aand Harrisonn, GENA Woorkshop 20009 Figuree 2: Labeling the t backs of th he chromosom mes 9 Terry and Harrison, GENA Workshop 2009 STUDENT HANDOUT: 1. Sort Mom’s and Dad’s chromosomes You and your partner have two envelopes, one labeled Dad (male) and the other labeled Mom (female). Choose one of these envelopes. Take all of the chromosomes out the envelope and make sure the white side of each of the chromosomes (showing the picture of the chromosome) is facing up. Now, sort them by pairs. There should be 16 total chromosomes or 8 pairs of homologous chromosomes. 2. Produce “gametes” by meiosis Pretend that your desk (or workspace) is a cell undergoing meiosis. Line up the 8 pairs of chromosomes along an imaginary line at the center of your desk or workspace. Check the diagram of meiosis in your textbook and make sure your chromosomes look like they should in metaphase I of meiosis I. Then, use your chromosomes to demonstrate what happens during anaphase I of meiosis I. Draw the four gametes what would result after meiosis II had taken place. Without turning your chromosomes over to the colored side, choose one of the resulting gametes to use in part 4. Put these aside and continue to step 3. 3. Repeat Steps 2 and 2 for the other parent’s chromosomes 4. Model the process of fertilization. Mix the chromosomes from mom’s egg and dad’s sperm together. 5. Determine the child’s genotype and phenotype Flip over the chromosomes (to the colored side) and line them up by pairs. Write the offspring’s genotype in the table. Use the chart to determine the offspring’s phenotype. 6. Draw the face of the offspring Use the information from the table on the student worksheet to draw what your offspring would look like. 7. Compare features of siblings to one another and to mom and dad 10 Terry and Harrison, GENA Workshop 2009 STUDENT WORKSHEET The Genetics of Parenthood Data Sheet Parents _____________________________ and ______________________________ Fill in data table as you determine each trait described in the Guidebook. Allele from Mom Allele from Dad Face shape A a A a Eye size B b B b Nose size C c C c Hair type D d D d Lips E e E e Ears F f F f Chin G g G g Sex X X X Y TRAIT Child’s Child’s Genotype Phenotype Key to Traits: Face shape: Eye size: Nose size: Hair: Lip shape: Ear lobes: Chin shape: Round – AA or Aa Large – BB Large – CC or Cc Curly – DD or Dd Thick – EE or Ee Attached – FF or Ff Round – GG or Gg Medium - Bb Square aa Small – bb Small – cc Wavy – dd Thin – ee Free – ff Square - gg 11 Terry and Harrison, GENA Workshop 2009 Face shape: Round – AA or Aa Square – aa Eye size: Large – BB Medium - Bb Small – bb Nose size: Large – CC or Cc Small – cc Hair: Curly – DD or Dd Wavy – dd Lip shape: Thick – EE or Ee Thin – ee Ear lobes: Attached – FF or Ff Free – ff Chin shape: Round – GG or Gg Square – gg (shown on a round face) 12