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WebLab3: Exercise1
Discovering Chromosomes
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Objectives:
- To distinguish between the nuclei of eucaryotic cells whose DNA is contained in many linear chromosomes, and the nuclear region of procaryotic cells containing a single circular DNA molecule.
- To distinguish between different types of chromosomes based on the position of the centromere.
- To create and submit karyotypes from photos of cell squashes of eucaryotic cells.
- To explain translocations, deletions, and selected abnormal chromosomal syndromes: Down's, Klinefelter's.
- To identify chromosomal defects through karyotype creation and
analysis.
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Materials:
- A computer, a printer, and an ISP (Internet Service Provider).
- Several sheets of white bond (typing paper), scissors, and transparent
tape.
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Methods:
- Read the background information
to help prepare you for the content of this exercise.
- Go to The
Genetic Science Learning Center,sponsored by the University
of Utah, and read the Introduction to Chromosomes. Download and
print the picture of the chromosomes on that page. Carefully cut
each chromosome out from your printed image and try arranging
them in pairs on your typing paper (from now on called your "answer
paper") based on
- chromosome size
- centromere position
- staining patterns.
- What you just did in the step above is create a Karyotype! Now
you'll go to find out
What Chromosomes can tell us. Reading this section will
give you insight into the meaning of the karyotype you created.
Note that the chromosomes you are looking at on this page are
diagrams of real chromosomes, like the ones you drew from the
photo of the cell squash. The diagrams are a lot easier to look
at. Write out the meaning of
- metacentric chromosome
- submetacentric chromosome
- acrocentric chromosome
on your answer paper.
- Now go to The
Karyotype Match-up Page and observe the four karyotypes presented
there (lettered A, B, C, and D):
- a 47 chromosome, trisomy-21 (Down's syndrome) individual
(see Down's Syndrome
for more information)
- a normal male (see Normal
Male for more information)
- a normal female (see Normal
Female for more information)
- an individual with Klinefleter's syndrome (47 chromosomes,
with an extra X chromosome)
Take your time with this section. Read all sections of the backgroud
information link included there. And carefully look at the "after-shots"
to try to understand the meaning of being a genetic male, and
a genetic female. Is an individual with Klinefelter's syndrome
male or female? Answer this question on your answer paper. Go
to Klinefelter's
Syndrome for further backgroud information about this 47,
XXY chromosomal abnormality to help you interpret the karyotypes.
Go to the "Want to know more?" link at the bottom of
the Klinefelter page for a fundamental explanation of genetic
sex determination.
- Go to
The Mixed-Up Pieces page and, on your answer sheet, write
out the definition of the following terms:
- Translocation
- Reciprocal translocation
- Robertsonian translocation.
There are three links on this page. Find the one that explains
why a translocation can be associated with a type of leukemia
(chronic myelogenous leukemia, CML). Provide (on your answer sheet)
your own clear explanation of why translocations can lead to an
abnormal cell function like cancer.
- Go to the
Missing Pieces page and, on your answer sheet, describe the
Cri-du-Chat Syndrome, and explain how the William's Syndrome deletion
can cause heart problems.
- Submit your answer sheet in class.
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