Download Terry and Harrison, GENA Workshop 2009 1 Meiosis and Genetic

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.
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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.
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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).
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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).
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Attachment #1
Pre-test/Post-test
NOTE: This will be uploaded separately.
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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.
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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.
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Figure 1: The Parents' Chroomosomes
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Figuree 2: Labeling the
t backs of th
he chromosom
mes
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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
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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
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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)
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