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Station 5
Nondisjunction is the failure of two members of a homologous pair of
chromosomes to separate during meiosis. It gives rise to gametes with a
chromosomal content that is different from the norm. The consequences of
this are usually quite severe, and a number of clinical conditions are the result
of this type of chromosome mutation.
1. Define Nondisjunction.
2. Use the diagram to describe what happens during meiosis that results in
Klinefelter’s male.
3. Use the diagram to describe the process that occurs in meiosis that
results in an XYY male.
Station 6
In the diagrams below, label each stage of meiosis on your answer sheet using
the following terms: Prophase I, Prophase II, Metaphase I, Metaphase II,
Anaphase I, Anaphase II, Telophase/Cytokinesis I, Telophase/Cytokinesis II
Station 7
In the table below, label each stage of meiosis on your answer sheet using the
following terms: Prophase I, Prophase II, Metaphase I, Metaphase II, Anaphase I,
Anaphase II, Telophase/Cytokinesis I, Telophase/Cytokinesis II
**terms may be used more than once or not all all**
Name of Phase
Homologous chromosomes pair up and form tetrad
Spindle fibers move homologous chromosomes to opposite sides
Nuclear membrane reforms, cytoplasm divides, 4 daughter cells
Chromosomes line up along equator, not in homologous pairs
Crossing-over occurs
Chromatids separate
Homologous line up alone equator
Cytoplasm divides, 2 daughter cells are formed
Station 8
On the lines provided on your answer sheet, order the different stages of
meiosis I THROUGH meiosis II, including interphase in the proper sequence.
1. _____________
3. _____________
4. _____________
6. _____________
8. _____________
homologous chromosome line up in the center of the cell
spindle fibers pull homologous pairs to ends of the cell
4 haploid (N) daughter cells form
cells undergo a round of DNA replication
sister chromatids separate from each other
2 haploid (N) daughter cells form
spindle fibers attach to the homologous chromosome pairs
individual chromatids move to each end of the cell
crossing-over (if any) occurs
Station 9
Haploid & Diploid Background Information
All animal cells have a fixed number of chromosomes in their body cells which exist in
homologous pairs (2n). Each pair of chromosomes consists of one chromosome from
the mother and the second from the father. During the process of meiosis, the sex cells
divide to produce "gametes" which then contain only one set of the chromosomes (n).
When the male gamete (sperm) and the female gamete (egg) fuse during fertilization
and zygote formation, the chromosome number is restored to 2n again. Thus, diploid
cells are those which contain a complete set (or 2n number) of chromosomes
whereas haploid cells are those that have half the number of chromosomes (or n) in
the nucleus. Gametes (sperm and egg) are haploid cells and somatic cells are diploid.
The number of chromosomes (n) differs in different organisms. In humans a complete
set (2n) comprises of 46 chromosomes.
Haploid cells are a result of the process of meiosis, a type of reduction cell division in
which diploid cells divide to give rise to haploid cells. During meiosis, a diploid cell
divides to give rise to four haploid cells in two rounds of cell division.
1. What is the difference between a haploid and diploid cell?
2. For each of the following state if the cell is haploid or diploid.
Sperm cell =
Liver cell =
Egg cell =
Stomach cell =
3. If the diploid number in a liver cell is 52, how many chromosomes are there in the
egg of this organism?
4. The combination of a _______ and an ______ produces a zygote with 46 chromosomes.
5. Meiosis produces haploid reproductive cells called ___________________.
6. Name the 2 human gametes & tell their chromosome number.
Station 10
What’s the difference between sister chromatids and homologous chromosomes?
Sister chromatids are (mostly) identical! It’s basically a copy (“replicate”) of the
original chromatid. Homologous chromosomes only share the same size and
shape – they may contain the same genes, but they may or may not be the same
version in each chromosome of the pair. One comes from the father and one from
the mother. Crossing over occurs between these (NOT between sister
1. Draw a picture that shows the difference between a chromosome, sister
chromatids, and homologous chromosomes.
Station 11
Use the DNA Fingerprints below to answer the questions in the boxes.
dad 1
dad 2
Lt. Russ is investigating a murder
scene. The felon was scratched by
his victim & some of his skin cells
were found under the victim’s
fingernails. A DNA test was
performed. Which of the suspects
is the murderer?
Mrs. Smith has a baby named
Jessica. She believes one of
two men can be the father of
her child. A paternity test is
done and the results are
shown above. Which of the
2 men are Jessica’s father?
Station 12
Gel Electrophoresis
Before DNA can be analyzed with gel electrophoresis, restriction enzymes
must be applied. Restriction enzymes work like “molecular scissors” cutting
the long DNA molecules at different locations. Where they cut depends on the
code within the DNA molecule and the code within the enzymes. For example,
one type of enzyme cuts DNA wherever it encounters a sequence AGCTT. The
length of these fragments will vary from person to person because the code
for every person’s DNA is different. Some fragments will be long, others short.
After DNA is cut using restriction enzymes, it is micropipetted into a well
within an agarose gel. Agarose gel is a thick, porous, Jell-O like substance. It
will act as a molecular strainer, allowing smaller pieces of DNA to move
through it more easily than larger pieces.
The agarose gel containing the DNA samples is placed in an electrophoresis
chamber. The DNA fragments have a slight negative charge so they move
toward the tray’s positive end. Smaller DNA fragments travel further toward
the tray’s opposite end than do larger DNA fragments. When electrophoresis
is complete, the fragments are distributed in the gel according to their lengths.
1. What do restriction enzymes do to the DNA?
2. What is agarose gel and how does it work?
3. Where is the DNA placed in the gel electrophoresis apparatus?
4. How does electrophoresis work?
Station 13
STEP 1: Determine what kind of problem you are trying to solve.
STEP 2: Determine letters you will use to specify traits.
STEP 3: Determine parent’s genotypes.
STEP 4: Make your punnett square and make gametes
STEP 5: Complete cross and determine possible offspring.
STEP 6: Determine genotypic and phenotypic ratios.
A tall green pea plant (TTGG) is crossed with a short white pea plant (ttgg).
TT or Tt = tall
GG or Gg = green
tt = short
gg = white
A tall green pea plant is crossed with a tall white pea plant
___________ X ___________
____ Tall/Green : ____ Tall/White : ____ Short/Green : ____ Short/ White
Station 14
In mice, the ability to run normally is a dominant trait. Mice with this trait are
called running mice (R). The recessive trait causes mice to run in circles only.
Mice with this trait are called waltzing mice (r). Hair color is also inherited in
mice. Black hair (B) is dominant over brown hair (b).
A heterozygous running, heterozygous black mouse is mated with a
homozygous running, homozygous black mouse. What are the possible
genotypes and phenotypic ratios?
____________ X ____________
Station 15
Sex-linked traits are those whose genes are found on the X chromosome but not on the Y
chromosome. For each of the genes that are exclusively on the X chromosomes, females,
who are XX, would obviously have two alleles. Males, who are XY, would have only one
allele. Thus females with one recessive allele and one dominant allele, for a gene that is
unique to the X chromosome, will always display the dominant phenotype. However, a
male with a recessive allele for a gene unique to the X chromosome will always exhibit that
recessive trait because there is no other corresponding allele on the Y chromosome.
Use the information below to answer the following questions.
XH- X chromosome with normal dominant allele (no hemophilia)
Xh - X chromosome with recessive hemophilia allele
Y - Y chromosome (does not contain comparable gene)
XB - X chromosome with normal dominant allele (not colorblind)
Xb - X chromosome with recessive colorblind allele
Y -Y chromosome (does not contain comparable gene)
1. A normal-sighted woman, who has a colorblind father, marries a colorblind man.
What is the probability that they will have a son who is colorblind? What is the
probability that they will have a colorblind daughter? Complete the Punnett square.
2. What is the probability that a colorblind woman who marries a man with normal
vision will have a colorblind child? Complete the Punnett square.
Station 16
1. How many pairs of autosomes does this karyotype have?
2. How many pairs of sex chromosomes does this karyotype have?
3. What do you notice about the X and Y chromosomes?
4. What is the sex of this organism?
5. Looking at all of the pairs, do you see any different circumstances? What
is the special circumstance that you find?
6. What kind of effect do you think this abnormality on chromosome pair
#21 will have on the organism?
Station 17
1. What is the sex of this organism?
2. Are there any trisomy’s in this karyotype? If so, which chromosome pair
is a trisomy?
3. What would you expect to see in the number of genes on chromosome
Station 18
Diabetes and Genetics
In Type 1 diabetes, the body does not produce insulin. The body breaks down the sugars
and starches you eat into a simple sugar called glucose, which it uses for energy. Insulin is a
hormone that the body needs to get glucose from the bloodstream into the cells of the body.
Type 1 and Type 2 diabetes have different causes. Yet two factors are important in both.
You inherit a predisposition to the disease then something in your environment triggers it.
Genes alone are not enough. One proof of this is identical twins. Identical twins have
identical genes, yet when one twin has type 1 diabetes, the other gets the disease at most
only half the time.
In most cases of type 1 diabetes, people need to inherit risk factors from both parents. It
seems that these factors must be more common in Caucasians because they have the
highest rate of type 1 diabetes.
Because most people who are at risk do not get diabetes, researchers want to find out what
the environmental triggers are. Some are believed to be cold weather and viruses.
Type 1 diabetes is generally considered to be an autoimmune disorder. Autoimmune
disorders occur when the immune system attacks the body's own tissues and organs. For
unknown reasons, in people with type 1 diabetes the immune system damages the insulinproducing beta cells in the pancreas. Damage to these cells impairs insulin production and
leads to the signs and symptoms of type 1 diabetes.
Type 2 diabetes is non-insulin–dependent diabetes, and usually is caused by genetic predisposition to insulin receptors malfunctioning when other risk factors are present like
obesity, lack of exercise and poor diet.
Feedback Loops
Homeostasis in the body is maintained by internal feedback mechanisms called negative
feedback. Negative feedback returns a system to a set point once it deviates sufficiently
from that set point. This is how blood glucose levels are controlled. The pancreas has a
crucial role in the production of the hormones insulin and glucagon which work together to
maintain homeostasis. When blood glucose levels are high, the pancreas releases insulin.
Insulin signals body cells to accelerate the conversion of glucose to glycogen, which is
stored in the liver. When blood glucose levels are low, glucagon is released from the
pancreas. Glucagon binds to liver cells, signaling them to convert glycogen to glucose and
release the glucose into the blood.
Glucose Regulation
In the following illustration use the phrases found in the word bank to show the feedback
loop described on the previous page.
*Glucagon secreted from pancreas
*Blood glucose decreases; insulin secretion inhibited
*Glycogen forms from glucose
*Blood glucose increases; glucagon secretion inhibited
*Insulin secreted from pancreas
*Glucose forms from glycogen