Case Study Task: Diagnose the Patient

Genetics Case Study: Diagnose the Patient

Task: work through this case step-by-step in groups. Discuss your thinking each step of the way.

Start with Step 1. Complete all test in Step 2 before moving to Step 3. You will need internet access for Step 3 only. You will need access to the syllabus and a textbook throughout.

Step 1: The Case History

Patient: 19 year-old African-American male.

Credits for this task are at the end of the sheets.

What do you want to do next?Family History Blood protein structureObserve blood sample DNA sequencing

Stephen Taylor, Bandung International School http://sciencevideos.wordpres.com

http://sciencevideos.wordpres.com/

http://sciencevideos.wordpress.com/


Step 2: Family History

Create the patient’s family history using the clues in the case history and this template pedigree chart.

You will need to shade in some of the squares and circles.

a. Define allele.

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b. Distinguish between recessive and dominant alleles.

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c. Deduce, with a reason, which type of allele is causing this illness.

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Step 2: Blood sample

The slides below are light-micrographs of erythrocytes from a healthy person and from the patient.

a. Calculate the width of a normal erythrocyte.

b. Calculate the magnification of these images.

c. Describe how the patient’s erythrocytes differ from a healthy person’s.

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d. Suggest reasons why the patient felt some of his symptoms.

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Step 2: Blood protein structure

The images below represent the 3D structures of hemoglobin in a healthy person and in the patient.

a. Outline the differences in the two Hb structures.

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b. Suggest how this might lead to a difference in red blood cell shape.

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c. Label the diagrams above to identify levels of protein structure which are apparent.

d. Explain what genetic factors determine protein structure and therefore why these two proteins are so different.

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Step 2: DNA Sequencing

The gene for Hb production is called HBB and is found on chromosome 11 at locus 11p15.5. The gene of the patient was sequenced and compared to that of a healthy sample. Transcribe and translate this section of the gene. You do not need to look for the start codon.

Don’t forget – we transcribe the antisense strand!

a. Define gene locus.

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b. Identify the type of mutation which has occurred in the base sequence of DNA.

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c. Identify the amino acids present in both the normal and patient polypeptides.

Normal: ………………………………………………………………………………………………………………………………

Patient: ………………………………………………………………………………………………………………………………

d. Draw simple structural diagrams of the amino acid which is normally present and its replacement in the patient. Explain how the properties of these amino acids lead to differences in tertiary structure of proteins.


Step 3: The Diagnosis

Deduce the illness, using all the evidence presented in this case study.

Illness: _________________________________

Reasons:

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Confirmation: search for the gene and location in the NCBI’s gene database:

http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene (search hbb gene 11p15.5)

Were you correct? _____________

Try searching the names of three other genetic diseases that you know of. Where are they located and what causes the illness?

Genetic disorder Location (gene locus and name) Effects of mutation

Phenylketonuria (PKU)

Consolidation:

Use the class presentation and worksheets to complete notes on the section chromosomes, genes, alleles and mutations. Also, what connections can you make with the Chemistry of Life topics?

Credits:

This activity is heavily based on

“The Mystery of the Crooked Cell” http://web.mst.edu/~djwesten/Images/Crooked_Cell.pdf,

By Donald A. DeRosa and B. Leslie Wolfe Adapted by The Institute for Genomic Research

The adaptations made here are to allow for the task to be carried out in a low-tech environment and to directly related to the IB Biology course for high school.

Completion of the database tasks in step 3 satisfies the requirements for accessing databases in the 4PSOW.



http://web.mst.edu/~djwesten/Images/Crooked_Cell.pdf

http://sciencevideos.wordpress.com/bis-ib-diploma-programme-biology/04-genetics-and-genetic-engineering/chromosomes-genes-alleles-and-mutations/

http://sciencevideos.wordpress.com/bis-ib-diploma-programme-biology/04-genetics-and-genetic-engineering/chromosomes-genes-alleles-and-mutations/

http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene






Education

Case Study Task: Diagnose the Patient