Bio A – Cell division
What Can Chromosomes Tell Us?
Mitosis and meiosis are critical for creating normal cells. If a cell does not have all of its normal genetic
information, it cannot work properly. Errors in separating chromosomes can be catastrophic because the
lead to a cell having an extra chromosome or lacking a chromosome. In meiosis, the cells ultimately
created are gametes, or sex cells (egg or sperm). As these are the cells used to create a new organism,
improper crossing over or failure to separate homologous chromosomes can affect every cell in the
offspring’s body. It is possible to examine an individual’s chromosomes to look for major errors, if you
examine cells going through mitosis. Finding examples of each chromosome present and organizing
them into the homologous pairs is called karyotyping, and a karyotype can be used to identify the
genetic sex of an individual or to diagnose certain disorders.
Karyotypes
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Go to my website go to the unit page for the Cell Cycle and Cell Division. Find the links for
“Karyotypes”
Start with “Chromosomes and Inheritance” or type in
http://learn.genetics.utah.edu/content/chromosomes/
Under the Heading “Karyotypes”, read “How Do Scientists Read Chromosomes?”
o Identify three characteristics that you can use to “match” chromosomes. Be as specific as
possible.
o Since we need the DNA to be in chromosome form, do we want to look at actively dividing
cells or cells in G0? Explain.
Now go back to “Chromosomes and Inheritance” click on “Make A Karyotype.” Go through the
activity so that you can practice pairing up chromosomes.
o Are there any abnormalities in your patient?
o Is your patient male or female? How do you know?
Click back to “Chromosomes and Inheritance” and click on “Using Karyotypes to Diagnose
Genetic Disorders.” Read through and watch all the short animations. Use the information to help
answer the following questions.
o At the end of meiosis how many chromosomes should each human gamete have?
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Bio A – Cell division
o How do we ensure that a baby is born with the full 46?
Non-disjunction is a mutation that occurs when a duplicated chromosome fails to separate during
anaphase. Draw a sketch below of the daughter cells of a parent cell that normally has 4 total
chromosomes, but imagine that in anaphase I, one set of homologous chromosomes did not
separate normally. So you are showing me two haploid daughter cells whose chromosomes are
still replicated. Check your book or other sources if you are having trouble with this.
o Explain how a cell with a trisomy forms. Be specific!
o Explain how a cell with a monosomy forms. Be specific!
Click on the links to find out about the examples of genetic disorders resulting from too many or
two few chromosomes and summarize the causes and effects of the disorders. Identify the
specific chromosomes involved and whether each condition results from a monosomy or trisomy.

Klinefelter Syndrome:

Turner Syndrome:
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Bio A – Cell division

Down Syndrome:
Now go to:
http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping2.html
Complete the karyotypes for patients A, B and C and diagnose each one. Write your diagnoses
below:
o A:
o B:
o C:
Analysis Questions:
1.
The chromosomes for the karyotypes you have examined are all single, unreplicated
chromosomes. During what phase of the cell cycle would they look like this? Explain.
2. Why don’t we use cells going through meiosis for diagnosing with a karyotype?
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Bio A – Cell division
3. The incidence of Trisomy 21 increases dramatically as the mother’s age increases. A couple in
their early forties are having a baby and want to know if the fetus has Trisomy 21. Go to
http://anthro.palomar.edu/abnormal/abnormal_2.htm to learn about the three methods available
for obtaining DNA from the developing fetus. Create a table to compare the methods on
gestational age at which the test is done, accuracy in detecting Trisomy 21, and risk to the mother
or fetus associated with each.
4. Genetic disorders like hemophilia (blood does not clot normally) are due to a mutation in a single
gene. Could a karyotype be used to detect hemophilia? Explain
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Bio A – Cell division
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