Download Pre-lab homework Lab 4: Meiosis

Biology 102
PCC, Cascade
Pre-lab homework Lab 4: Meiosis
Lab Section:
Name:
1. Briefly explain the following terms in your own words. (You may use any resource you can find,
textbook, website, instructor..., but you need to try to use your own words!) .
•
Chromosome:
•
Gene:
•
Allele:
•
Haploid:
•
Diploid:
•
Gamete
•
Zygote
2. Mitosis and Meiosis are both types of cell division that start, in humans, with a single diploid cell.
How are the cells produced by the processes different?
 Continued on Back! 
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3. For each of the following phases of meiosis draw out the chromosomes from an organism that has 3
different types of chromosomes (n=3). The chromosomes need to be drawn so that you can see if
they are duplicated or not and the three types should be represented by three different lengths of
chromosomes. (Hint: If it has three types of chromosomes it will have 6 chromosomes in a diploid cell (2n=6)!)
The cells in Metaphase II has been drawn for you
Metaphase I
Anaphase I
Telophase I
Telophase I
Metaphase II
Metaphase II
Telophase II
Telophase II
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Lab 4: Meiosis
Goals: After successfully completing this lab, a student will be able to:
•
List the main occurrences of Meiosis including the major events of each phase.
•
Explain the processes that give rise to variation in the gametes produced by meiosis.
•
Describe the advantages and disadvantages of this variation in terms of reproduction.
Overview:
During your lifetime you have grown from a single celled zygote into an organism made up of
many trillions of cells. The vast majority of these cells are as close to genetically identical as your
body can manage. A few cells in your body though are very different. These cells are reproductive
cells called gametes, sperm or eggs, and they are genetically very different from your other body cells.
The cells that give rise to sperm and egg start out, just like any other cells in your body, in the G1
stage of the cell cycle. When triggered to divide they pass through S, when all the chromosomes in the
nucleus are duplicated, and G2, where the cells prepare for cell division. But the process of division in
these cells is different from mitosis and the products are also different. Mitosis produces two
genetically identical daughter cells but meiosis produces four cells and each one of these cells has half
the number of chromosomes that they started with and each cell is genetically different from the
others. In lab this week we will go over the process of meiosis and see how it can generate these cells
and we will see how the variability of these cells is responsible for much of the variety that we see in
the world around us.
Exercise 1: Modeling Meiosis with Pop Beads
In this exercise you will be modeling the movement of chromosomes through the eight phases
of meiosis. To begin you will need to get a bag of pop beads. These beads will be strung together to
represent chromosomes and you will then use them to demonstrate the stages of meiosis just like you
did when you modeled mitosis a few weeks ago. Recall that we learned that humans have 23 different
types of chromosomes and each of your cells (except sperm or egg cells) have two versions of each of
these chromosomes for a total of 46 in each cell. This is a result of the way that humans reproduce. For
every type of chromosome you have two versions, one inherited from your father and one inherited
from your mother. Scientists use the term diploid to describe this situation where there are two
versions of each chromosome. In sperm or egg cells the situation is a little different. If these cells had
46 chromosomes then when they fused the resulting cell would have 92 chromosomes, clearly this is
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not what happens. When your bodies produce these sex cells they use the process of meiosis to reduce
the number of chromosomes from two of each type to one of each type. Cells with one of each type of
chromosome are called haploid.
Procedures:
1. Count out your beads – you will need 38 red beads and 38 yellow beads to build your
chromatids. You will also need 8 of the magnetic “centromeres”
2. Assemble your large chromatids by building a chain of 4 red beads and a chain of 8 red beads
and joining these chains to a centromere. Now repeat this to produce another red chromosome
and then do the same thing with yellow beads to produce a total of 2 red and 2 yellow long
chromosomes. (see Fig. 2.2)
3. Assemble your small chromatids by building a chain of 3 red beads and a chain of 4 red beads
and joining these chains to a centromere. Now repeat this to produce another red chromosome
and then do the same thing with yellow beads to produce a total of 2 red and 2 yellow short
chromosomes. (see Fig. 2.2)
Figure 2.2 Your chromatids
Long chromatid
You will build 4 long (2 red and 2 yellow)
and 4 short (2 red and 2 yellow) chromatids.
Centromere
Short chromatid
4. Once you have your chromatids assembled you can begin to model the stages of the cell cycle
using these pop-bead models.
5. Try to go through one entire round of meiosis with the pop beads to get a feel for the process
then move on to exercise 2.
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Exercise 2: Modeling meiosis and Crossing over
In this exercise you will be modeling meiosis but this time we will be tracking different
versions of genes that are found on the chromosomes. By tracking the genes closely we can see more
clearly how the process of meiosis gives rise to a tremendous amount of variation in the cells it
produces. In this exercise we will use pieces of tape to distinguish regions of chromosome that contain
a gene and we will use letters written on the tape to represent slightly different versions of these genes
called alleles.
Procedures:
1. To be able to track the genetics of meiosis we will need to label the chromosomes with pieces
of tape. We will use these pieces to represent different genes. Since genes are always found in
the same place on a chromosome we will all put our tape pieces on the same place. You will
place your first piece of tape two beads in on the short arm of the long chromosome, your
second piece on the long arm three beads in and your last piece on the fourth bead of the long
arm of the short chromosome. (see Fig. 4.1)
Short Arm
Long Arm
Figure 4.1
The placement of genes
on your chromosomes
 gene 1
 gene 2
 gene 3
2. Once you have your genes labeled you will need to distinguish different versions of the genes
from each other. These different versions, called alleles, may be responsible for building
different proteins that have a large effect on the way an organism looks. For example different
alleles of a gene that builds a protein that is part of a hemoglobin molecule determine if you
will be born with sickle cell anemia or not. For each piece of tape you will need to write either
+ or a – sign. To decide which chromosome gets which you will role a die for each of the
genes. If you role a 1, 2 or 3 the + goes on the red chromosome. If you role a 4, 5, or 6 the +
goes on the yellow chromosome.
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3. Now you are ready to model the process of meiosis in more detail. This time you will model
two events in more detail – Crossing over and the line up of chromosomes during Metaphase I.
a. Crossing Over: To model crossing over, which is the process that results from the
breaking and swapping of DNA strands in the chromosomes, you will need to pair your
chromosomes up. Place your long red chromosome next to the long yellow and the
short red next to the short yellow. With your two long chromosomes lined up next to
each other start at the joint between the first and second bead of the long arm. Role the
die and if it is a 6 then break apart the joints on both the red and yellow chromatids that
are right next to each other and swap the chromosome tips. If the die roles a number
other than 6 then you do not swap the beads at this joint. Either way after finishing this
first joint move down to the joint between the second and third beads and roll the die
again. If the role is a 6 then cross-over at this joint and then keep moving on through all
the other joints. Every time you role a 6 you should break open the joint and cross over.
After you have finished with the long chromosome go through the short checking for
cross over at each of its joints.
b. Line-up: After checking for crossing over on both the chromosomes it is time to set up
the chromosomes for metaphase. Notice that the process of crossing over forces the two
chromosomes of the same type to be next to each other. These chromosomes, called
homologous chromosomes, now will line up for Metaphase I in pairs. To determine
which chromosome goes on each side we will once again allow chance to dictate. To set
up the long chromosomes role the die and if the number is a 1, 2, or 3 then the
chromosome with the most red beads will be on the left. If the number is a 4, 5, or 6
then the chromosome with the most yellow will be on the left. Now repeat this for the
short chromosome (1,2,3 = red on left; 4,5,6 = yellow on left).
4. Now go through the rest of meiosis until you have produced 4 haploid sex cells. These cells are
now called gametes and just need to find another gamete to fuse with so that they can make a
new diploid cell called a zygote!
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Exercise 3: Random Fertilization
In this exercise you will model random fertilization, this is the final place where variation is
added during sexual recombination. As you will see in the video this process of picking mates is often
anything but random, for now though we will randomly select gametes to fuse together to produce
offspring. This process is clearly more complicated than we will be modeling today but we are really
just looking for the genetics of what is going on
Procedures:
1. Line your gametes up in a row in front of you. Now role the die twice, add the numbers
together and starting from the left count through the gametes one at a time until you reach the
number you rolled. This is the gamete you will be taking over to another group.
2. Find another group who needs to create a gamete and join your gamete to theirs. Record the set
of alleles found in your new offspring in the chart below and then collect the information from
the other groups. You may need to make two zygotes if there is a group that cannot find a
“mate”. If this happens just randomly chose one of your remaining gametes to use for
fertilization.
Group
Example
Alleles for gene 1
Alleles for gene 2
Alleles for gene 3
+/-
+/+
-/-
#1 (your group)
#2
#3
#4
#5
#6
#7
#8
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Biology 102
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Exercise 4: Why Sex?
In this exercise you will be watching a video that asks the question why do organisms have sex.
This video also presents several new concepts related to evolution including the idea of evolution
through sexual selection and the hypothesis that human intelligence is at least partially the result of
sexual selection.
Procedures:
Read these questions prior to watching the video and answer them during the video!
1. What is the reproductive strategy for almost every animal?
2. Was black spot disease in minnows more likely to infect asexual or sexual reproducers? Why?
3. What is the Red Queen idea?
4. What is a benefit of sexual reproduction?
5. Give some examples of ornamentation found on males in the animal kingdom.
6. How did the peacock offspring fathered by males with small trains compare to those fathered by
males with large trains?
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7. Why do you think it is important that the traits used in sexual selection indicate the fitness of the
mates?
8. What is a benefit of monogamy?
9. What brought about the gender role reversal in Jacana birds?
10. How do female chimpanzees reduce the killing of their young?
11. In the video they introduce the field of evolutionary psychology. One of these psychologists while
talking about the smell of molecules says that the smell is not in the molecule we smell but in the
brain that does the smelling. What does he mean by this? Do you agree?
12. What is so unusual about the baby that the human couple has? Why do you think this is uncommon
in the rest of the natural world?
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Pre-lab homework Lab 5: Vertebrate Reproduction
Lab Section:
Name:
1. Label these structures on the picture below: Spermatogonium, primary spermatocyte, secondary
spermatocyte, early spermatid, late spermatid.
Meiosis II
Mitosis
Meiosis I
2.
The oval below represents a cross section of an ovary. Shade in the area where you would find
primordial follicles, and draw a mature follicle and a corpus luteum.
3. Would all of these structures be present in a human ovary at the same time? Why/Why not?
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Lab 5: Vertebrate reproduction
Goals: After successfully completing this lab, a student will be able to:
•
Identify the main structures of the human reproductive system
•
Describe the use of these structures during human reproduction
•
Explain the process that is used to synchronize the ovarian and uterine cycles.
•
Briefly describe the process of fertilization and development that take place in humans.
Overview:
Almost all vertebrate animals reproduce exclusively through sexual means. Last week we saw that
biologists currently attribute this prevalence of sexual reproduction to the value of the variability that is
generated by sexual reproduction. In this lab we will focus more on the structures and process of
sexual reproduction in humans. Starting with an overview of the anatomy of male and female
reproductive systems we will see where meiosis in humans gives rise to gametes and how these
gametes are brought together. We will then examine in more detail the events and structures that give
rise to gametes in humans. We will then see how the events of the menstrual (or uterine) cycle are
controlled by events occurring in the ovary during the ovarian cycle. Finally we will watch the process
of development from fertilization of a human egg to birth and gain insight into how this process can
take a single cell and through mitosis generate an incredibly complex individual organism – a human
baby.
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Biology 102
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Exercise 1: Male reproductive anatomy
In this exercise we will use models and slides to help us understand the structures of the male
reproductive system and how they relate to fertility. In particular we will look at the organization and
structure of the testis and the path that sperm travels until it exits the penis.
Procedures:
3. Get a copy of an unlabeled diagram of the male and female reproductive system.
4. Go through the diagram with the model of male anatomy and fill in the labels of the following
structures: Epididymis, Ejaculatory duct, Penis, Prostate, Scrotum, Seminal Vesicle, Testis,
Urethra, Urinary bladder, Vas deferens.
5. Find the slide of the testes. Try to identify the tubes that are the site of sperm production and
see if you can identify cells in the various stages of sperm production.
Exercise 2: Female reproductive anatomy
In this exercise we will use models and slides to help us understand the structures of the female
reproductive system and how they relate to fertility. In particular we will look at the organization and
structure of the ovary and see how ovary cells change as they prepare for ovulation. We will also
examine the different structures responsible for taking care of the egg after ovulation.
Procedures:
1. Get a copy of an unlabeled diagram of the male and female reproductive system.
2. Go through the diagram with the model of female anatomy and fill in the labels of the
following structures: Cervix, Clitoris, Fallopian tube, Labia, Ovary, Urethra, Urinary bladder,
Uterus, Vagina.
3. Find the ovary slide and get it set up on the scope and then look for:
a. Primordial follicles: small cells usually around the outer edge of the ovary
b. Maturing follicle: the egg cell is developing and the follicle grows to include a fluid
filled chamber –meiosis I finishes in the cell that will become the egg
c. Corpus luteum: after releasing the secondary oocyte much of the follicle remains in
the ovary releasing hormones.
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Exercise 3: Ovulation and Menstruation
In this exercise you will look at the cycling hormones that drive changes in the ovary and
uterus that lead to ovulation and menstruation. As you will see these changes effectively tie together
events in the ovary and the uterus to ensure that both organs cycle together. We will also use this as an
excuse to talk about building and reading graphs and how to insure that your graphs convey
information clearly
Procedures:
1. Get a copy of the data table for human fertility hormones and a piece of graph paper from your
instructor.
2. Because both variables are continuous we will be drawing a line graph of our data. If the
variables were less continuous another type of graph might be good. For example if you have
discreet categories of information a bar graph can be a great way to represent information.
3. Prepare your line graph following these hints:
a. Think about what information you want your graph to convey. In this case we are going
to graph changing hormone levels throughout a month long cycle so the two parts of our
graph are time and hormone levels.
b. Assign each part of the graph to an axis – either up and down (called the Y-axis) or
horizontally (called the X-axis). It usually works out well to put your independent
variable on the X-axis and the dependent on the Y-axis. Once you have decided on what
goes where you need to label each axis.
c. Now you need to figure out the scale on each axis. To do this look at the numbers that
you will use and find the largest one. Now count how many lines you have on each axis
and divide the largest number you need to fit on the axis by the number of lines. This
will give you the smallest number each line needs to represent. You can always round
up but try if you keep close to this number it will keep your graph nice and spread out.
Once you have decided on the scale label each axis (usually every 5 lines is enough)
and make sure you clearly label the units.
d. Now you are ready to plot your points on the graph and then connect them with a line.
4. Once you have graphs for all your hormones (you can put them on the same graph just use
different colors for each and reset your axis each time) answer the questions on the next page.
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Exercise 3: Ovulation and Menstruation Continued
Questions:
1. Looking at your graphs, which hormones rise mostly before ovulation?
2. Which hormone rises mostly after ovulation?
3. Imagine you work for a company that produces fertility testing devices. Your boss, who is not a
biologist, says he wants to build a machine that measures hormone levels and can predict when
a woman will be most fertile. He wants you to decide which hormone(s) (you can pick one or
two) would be the best indicator that ovulation is coming. What do you tell him and why?
4. For each of the following hormones draw arrows to indicate how they affect each other. For
stimulation use an arrow with a plus and for repression use an arrow with a minus.
FSH
LH
ESTROGEN
PROGESTERONE
5. How do estrogen and progesterone affect the uterus?
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Exercise 4: Life’s Greatest Miracle?
In this exercise you will be watching a video that follows the development of a human baby as
it grows from a single fertilized egg into a baby that is ready to be born. This video also reviews some
of the material we covered last week including the role of meiosis in developing the variation that
seems so important for species survival.
Procedures: Read these questions prior to watching the video and answer them during the video!
1. All humans started from a single fertilized egg and passed through many rounds of mitosis to
becoming the organism we are now. Approximately how many cells are in an adult human?
2. What do they suggest is an advantage to sexual reproduction? A disadvantage?
3. How many sperm do men create each day?
4. How many eggs are women born with? How many do they have when they are in their early 30’s?
5. How long would it take human sperm to swim through the uterus? How long does it actually take?
6. What advantage is there to slowly releasing sperm from the cilia filled boarder of the fallopian
tubes?
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7. What does a fertilized egg look like at the point it implants into the uterus and how old is it?
8. What is gastrulation and what happens to the cells during this process?
9. How are cells able to communicate with each other and what does this do to their genes?
10. What does the gene SRY do and how long does it remain turned on?
11. During the last trimester what is happening to the brain and why?
12. Why are human birth’s more dangerous than most animals?
13. Imagine you are giving birth, who would you want in the room with you? Why?
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Pre-lab homework Lab 6: Heredity
Lab Section:
Name:
1. Briefly explain the following terms in your own words. (Looking them up is great but try to write
your answers with ideas from your head and not copying from a source!) .
•
Genotype:
•
Phenotype:
•
Heterozygous:
•
Homozygous:
2. In a cross between homozygous short pea plants and homozygous tall pea plants you find that all the
F1 plants are tall.
a. What allele is dominant? How do you know?
b. If you mated two of these F1 generation plants together to make an F2 what types of offspring
would you see and in what proportion?
3. The following symbols are commonly used in human pedigrees, next to each symbol write what it
stands for. (read the lab or look in your text for the answers)
or
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Lab 6: Heredity
Goals: After successfully completing this lab, a student will be able to:
•
Correctly use the terms genotype and phenotype to describe an organism.
•
Predict genotype and phenotype ratios from given crosses.
•
Explain the results of crosses using the concepts of segregation and independent assortment.
•
Build pedigrees from written descriptions of families and use these to deduce inheritance
patterns.
Overview:
The study of heredity has been important for humans for thousands of years. As crops and animals
became domesticated people started paying attention to the inheritance patterns of traits that led to
better yields of food or higher quality animals. In the middle part of the 1800’s a monk named Gregor
Mendel developed several new insights into inheritance based on his work tracking traits in pea plants.
When Mendel published his results they were widely ignored for nearly 40 years until several
scientists in 1900 came upon his work and recognized the importance of his ideas on inheritance. His
main ideas can be summarized as four points; 1. Alternative versions of genes account for the
variations we see in inherited traits – we call these versions alleles. 2. For each trait an organism
inherits two alleles, one from each parent. We now know this is due to the diploid nature of most
organisms. 3. If the two alleles an organism has are different one, the dominant allele, will determine
the appearance of the trait in the organism (called the phenotype) while the other, the recessive allele,
will have no outward effect on the phenotype of the organism. 4. During the production of gametes the
different alleles are separated into different gametes. This is often called the law of segregation since
the alleles will be segregated into different gametes and inherited separately from each other. Over the
last few weeks we have been following the processes that create gametes (meiosis) and join them
together (sexual reproduction) so you should not be surprised by the concept of alleles segregating
since it is caused by the movement of chromosomes in meiosis but at the time of Mendel there was
very little understanding of the nature of these processes. Mendel was able to deduce the existence of
genes and alleles and observe the effects of meiosis some 75 years before the structure of DNA was
discovered. This week we will examine several crosses in plants that illustrate the methods of Mendel
and we will see how the ideas these crosses help us develop will be useful in tracking inheritance
patterns in human families.
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Exercise 1: Monohybrid crosses
In this exercise we will examine the results of monohybrid crosses in corn plants. These
crosses track a single trait at a time in this case we will track either corn height (normal height corn or
dwarf corn) or corn color (green corn or albino corn). We will try to pay particular attention to the way
the alleles segregate in this cross to see how Mendel’s idea of segregation is apparent in our crosses.
After examining these corn plants you will then answer questions based on monohybrid crosses.
Procedures:
6. On the counter is a tray of corn plants that represent the F2 generation of a monohybrid cross.
This means that an initial cross of two pure breeding strains was made and then the offspring of
that cross (the F1 generation) were mated to each other to produce the plants that you see.
7. Find the tray your group is assigned to and count the numbers of each phenotype present and
then record them in the table below (Table 6.1)
8. After recording the phenotypes calculate the ratio by dividing the largest number by the
smallest and writing the answer in the following format (your answer: 1 )
9. Now record the data from another group who recorded results for the other cross and answer
the questions on the next page.
Table 6.1: F2 Offspring phenotype and ratio
Characteristic:
Common
Phenotype
Rare
Phenotype
Ratio
(Common/Rare:1)
Rare
Phenotype
Ratio
(Common/Rare:1)
Characteristic:
Common
Phenotype
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Exercise 1: Monohybrid Cross Continued
Questions:
6. From your results which trait do you hypothesize is dominant for each characteristic?
7. Assuming your hypothesis for question #1 is correct what were the genotypes and phenotypes
of the parents of the plants your group is examining? (The F1 generation)
8. Now write out a Punnett square for the cross in question 2 (F1 x F1) and make sure your
prediction matches your observation in Table 6.1. What happens if your results are not exactly
the same as your prediction? Does this mean your hypothesis is wrong?
9. Explain how your Punnett square in question #3 illustrates the idea of segregation that Mendel
came up with nearly 150 years ago.
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Exercise 2: Dihybrid crosses
In this exercise we will examine the results of a dihybrid cross in corn plants. This cross tracks
a pair of traits at the same time in this case we will track both corn height (normal height corn or dwarf
corn) and corn color (green corn or albino corn). This cross will illustrate the idea of segregation again
but we will also see an example of independent assortment, the idea that alleles for one trait will be
inherited independently of the alleles for other traits.
Procedures:
4. Look at the tray of corn labeled dihybrid cross. Notice that in this cross each plant has two
characteristics we are tracking, height and color. Because of this we will have four different
types of plants to look at, each with its own combination of traits
5. Once again these plants represent the F2 generation. In this case they are the offspring of plants
that are heterozygous for both alleles.
6. Remember that you already have a good idea about which allele is dominant for each of these
traits from exercise 1.
7. Now fill in Table 6.2 and answer the questions that follow.
Table 6.2: F2 Offspring from a dihybrid cross
Offspring phenotype
number
Tall and Green
Tall and White
Dwarf and Green
Dwarf and White
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Exercise 2: Dihybrid Cross Continued
Questions:
1. Which combination of traits is most common? Why do you think this is?
2. One of the alleles you worked with today, albino corn, is fatal when it is homozygous. Why do
you think this is?
3. Normally to create a plant heterozygous for two traits you first cross two pure breeding strains
to generate an F1 – so in this case you would cross a homozygous tall green with a homozygous
dwarf albino. Now, of course, the supply store that sells us the seed cannot do that – but they
need to be able to guarantee that the seeds we buy from them came from a cross of a
heterozygous tall green plant. How could you tell your plant was heterozygous if you can’t use
homozygous albino parents?
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Exercise 3: Human pedigrees
In this exercise we will look at pedigrees for two families and track the incidence of a disease
called sickle cell anemia. This disease is caused by an inherited change in the DNA that codes for a
polypeptide that is part of the protein hemoglobin. This protein is very common in your red blood cells
where it is responsible for transporting the majority of the oxygen the cells of your body consume. In
people with two copies of the allele for the sickle cell polypeptide the hemoglobin can form long
chains that distort the shape of the red blood cell. People with sickle cell anemia are prone to sickle cell
crisis that are caused by misshapen blood cells clogging tiny blood vessels.
Procedures:
5. You will need to draw out a pedigree for both of the families in this problem. Remember that
for these pedigrees you need to follow some simple rules. To indicate a male use a square (
or ), to indicate a female use a circle ( or ). A filled in symbol indicates someone who
has the trait. In this case someone with sickle cell anemia. A circle and a square joined by a
horizontal line indicates people who are married and a line coming down from them will attach
to a horizontal line that has their children as symbols hanging from it.
6. Get a description of the two families from your instructor and draw out a pedigree for each of
them. Try to do your best to figure out who is a carrier for sickle cell anemia – you can draw
their symbol half filled if you are certain they are heterozygous for the sickle cell allele.
7. You need to also get a slide showing “normal” red blood cells and another showing “sickle
cells” and sketch several cells from each slide in the space provided.
Normal cells
Sickle cells
8. Finally answer the questions on the next page.
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Exercise 3: Human Pedigrees continued
Questions: For these questions imagine you are a genetics counselor and Byron and Ava
(Children from the two different families you have created a pedigree for!) have come to talk
to you about their plans for having children after they get married.
1. Look at your pedigree for the Jones family – what are the genotypes of Dorothy and Leland?
What evidence are you using to determine this?
2. What are the genotypes of Mabel and Virgil Smith? What evidence do you have that this is
true?
3. What are the two possibilities for the genotypes of Byron and Ava? What are the chances of
them having either genotype? How do you know?
4. After hearing this Byron and Ava want to know if their children will have sickle cell anemia.
What do you tell them? Why?
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