Genetic diseases are inherited based on DNA, genes, and chromosomes. Genetic testing can identify certain inherited disorders, such as cystic fibrosis, as well as chromosomal abnormalities, such as Down syndrome. Fragile X, Turner syndrome, tay-sachs and hemophilia are all caused by genetic abnormalities. Genetic counselors look at family history, medical history and pregnancy history. Using this information, along with genetic testing, they are able to assess a person, or couple's, risk factors for a particular genetic disorder or disease. Genetic counseling can take place prior to pregnancy by looking at the parents genes or during pregnancy by using an amniocentesis.Couples with a family history of inherited disorders, those from certain ethnic groups, women exposed to toxins or women over 35 are all at increased risk of passing on genetic abnormalities.
In this lab we will analyze the pedigree chart and karyotype for two patients (Kayla & Emily). A karyotype is a picture of stained chromosomes arranged to show chromosome pairs. Abnormalities in chromosome number or size can be easily identified in a karyotype. Pedigree charts give a symbolic representation of phenotypic (observable) traits through a family. Using a pedigree researchers can trace the pathway of a disease through families.
Scenario 1
Kayla has a family history of Duchenne muscular dystrophy (DMD), which is a sex-linked trait. The patient wishes to know her risk of having an affected child. Her grandmother was a known carrier. DMD is an inherited disorder that involves progressive muscle weakness. It affects approximately 1 in 3500 male births worldwide and is inherited in an X-linked recessive pattern.
The following pedigree was drawn up by the genetic counselor. Our patient, Kayla, is #13.
What are the relationships between:
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1 and 2
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1 and 5
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1 and 10
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6 and 7
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4 and 5
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5 and 8
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8 and 10
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1 and 3
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What are the chances her mother was a carrier?
What are the chances our patient is a carrier?
What are the chances she passes the syndrome to a male child?
Testing would establish her status as eitherr a carrier or a noncarrier.
If she is a carrier what are the chance of her having an affected child?
If she is not a carrier what are the chance of her having an affected child?
Scenario 2
Emily, a forty year old pregnant woman has an amniocentesis which provides the karyotype below.
Using the karyotype above answer the following questions:
What is the gender of the fetus?
Are there any chromosomal abnormalities?
What would this chromosomal combination result in?
The real questions and scoring guide
- Explain the relationships between individuals on the pedigree.
- Explain the chances of patient's mother, patient, and male offspring being affected by the condition.
- Explain how the chances of the patient having a child with a specific syndrome differ depending on whether the patient is a carrier.
- Explain the results of the karyotype including the abnormal chromosomes and gender of the patient.