Lab 06 Handout

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is week, you will gain experience in constructing and interpreting karyotypes. Unlike “old-fashioned” karyotypesthat were generated from black-and-white photos, these karyotypes were prepared using a technique called FISH(fluorescence in situ hybridization). In FISH, fluorescently-labeled DNA molecules are allowed bind to specificchromosomes. ese “probes” allow you to identify homologous pairs and to distinguish between pairs by looking attheir patterns of colors. An example of a FISH karyotype is shown in Fig. 1. Note the banding patterns of thechromosomes, usually several per chromosome. Each band represents regions covering several hundred genes.

Activity 1. Constructing normal human karyotypes

Procedure:

1. Begin by cutting out the chromosomes on the sheet marked Karyotype 1.Once the chromosomes have been cut out, I suggest placing them on a sheet of white paper so you don’t losethem on the dark benchtop.

2. Using Fig. 1 as a guide, arrange each chromosome on the blank karyotype form. Do not fasten thechromosomes to the karyotype form until your instructor has checked it. Keep all paper scraps until you haveidentified each chromosome.

e chromosomes can be arranged in seven groups (A-G) according to length (see Table 1).

Fig. 1. A normal human karyotype, prepared using FISH.

Chromosomes and Karyotyping Instructions

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3. Once you are sure that Karyotype 1 is complete and correct, use the tape to secure the chromosomes to theKaryotype Form and complete the form.

4. Repeat this process with Karyotype 2. When you are finished, you will have two normal human karyotypes(male and female) that you will use as guides when completing your case studies.

Activity 2. Using karyotypes to diagnose genetic disorders

Now that you have established normal, baseline karyotypes, you will solve two cases that involve chromosomal errors.Loss or gain of chromosomal material is frequently but not always, associated with mental retardation. In the UnitedStates, approximately 20,000 infants are born with chromosomal abnormalities; each year this is about 1 out of every200 live births.

For each of these, I suggest counting the chromosomes before you begin cutting them out. is will give you an ideaof what type of disorder (if any) you are studying.

• e normal number of chromosomes is 46.

• If there are more than 46, there is extra chromosomal material and there are three possibilities: Downsyndrome (three copies of chromosome 21), Klinefelter syndrome (a male with two X chromosomes) or an

XYY male.

• If there are 45 chromosomes, the condition is Turner syndrome. When you prepare the karyotype of Turner syndrome, there will be only one X chromosome and no Y chromosome. Such people are females(45,X).

• If there are 46 chromosomes, the condition is fragile X syndrome. e karyotype of the fragile X syndromeis prepared by pairing chromosomes of the same size and shape. e staining technique used to show fragile

X produces opaque chromosomes. is is done to show the changed gene location on the end of the longarm (q) of the X chromosome. Be careful not to cut off the fragile site on the end of the X chromosome.

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Case 1.

Mr. and Mrs. Garcia are concerned about their three-year old daughter, Ana. Like all babies, Ana was chubby as sheput on weight after she was born. However, Ana did not seem to lose her baby fat. Her hands and feet wereespecially fat. e older Ana got, the more unusual she looked. She was unusually short, had low-set ears, droopingeyelids, and small, spoon-shaped nails. While each of these caused concern, but it wasn’t until Ana showed signs ofhearing problems that the Garcias were spurred into action.

Last week, the Garcias saw a daytime talk show that covered genetic illnesses and thought to themselves that Anamay have such a problem. e Garcias had always planned on having more children but are afraid that they may becarriers of a genetic disorder that they will pass on to other children.

Case 2.

Carolyn is a 44-year old woman who works at a pharmaceutical firm as a drug developer. She has recently found outthat she is pregnant, despite the fact that doctors had diagnosed her as infertile while she was in her early twenties.Because of her age, her obstetrician has strongly urged her to undergo amniocentesis, a procedure in which amnioticfluid is collected from the sac that surrounds the fetus. Carolyn is understandably nervous; her marriage is strainedand she fears that it won’t survive a difficult diagnosis. In addition, her job, though comfortable, is demanding. She

was already concerned that a child would complicate her life. Now, the idea of having a child with an incurableillness seems to be at odds with her career.

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Activity 1. Constructing normal human karyotypes

Chromosomes and Karyotyping Name ________________________________________

Lab Report

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Activity 2. Using karyotypes to diagnose genetic disorders

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Case 1.

1. Use the laptop to explore the internet to provide the Garcias with the name of a support group that they canconsult to get more information.

2. List two or three positive outcomes of this diagnosis that should make the Garcias feel better.

3. List two or three medical issues that her parents should keep an eye out for as Ana gets older.

4. Should the Garcias be concerned about having another daughter with this condition? Why or why not?

Case 2.

5. Is Carolyn’s fetus a boy or a girl?

6. What are some of the symptoms that Carolyn should expect to encounter with her baby?

7. Carolyn believes that some of the genetic problems in her husband’s family are to blame for this diagnosis. Do you agree? Why or why not?

8. Use the laptop to explore the internet to provide Carolyn with the name of a support group that she and herhusband can consult to get more information.

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Documents

Lab 06 Handout