Chapter 16 Assignment 1. Sandy and Robert are engaged to be married. They met at
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Chapter 16 Assignment 1. Sandy and Robert are engaged to be married. They met at their synagogue, and both have ancestors from Eastern Europe. Robert has a younger brother who has cystic fibrosis (CF). As far asSandy knows, no one in her family has had this disease. Robert isa nursing student and knows that the risk for CF is higher among Caucasian people, including those of Ashkenazi Jewish descent. He wants to have carrier testing done on Sandy. He figures that he must be a carrier and wants to se get genetic counseling and to money on having them both tested. A. Is Robert correct in assuming that he is a carrier? What is the probability that he is a carrier, considering that his brother is affected with CF? B. Sandy does not want to be tested. She says that no one in her family has ever had the disease, so she could not be a carrier. What could Robert say that could help her understand that she may still be a carrier? A woman of Catholic ancestry who has what she perceives to be a higher incidence of breast cancer in her family wants to be tested for the BRCA gene mutations but cannot afford to have it done through a physician's office because she has no insurance. For her birthday, her friends gave her money to be tested through 23ANDme, a company offering direct-to-consuming testing. Her results are back, and she is "negative." Is this helpful information? 2. 3. Distinguish between predispositional and presymptomatic genetic testing. Provide an example of a situation when each would be used. Copyright FADavis Plus 2019Explanation / Answer
1. A) CF is inherited in an autosomal recessive manner. As, his brother is affected (say,aa), and no information about their parent is available, both of them must be carrier (Aa) for the disease. Then Robert is correct in assuming that he is a carrier. The probability is 50% that he is carrier.
AaXAa will produce AA, Aa, Aa and aa genotypes.
B) Robert should say that as CF is an autosomal recessive disorder, no one can be affected by that disease, until he or she receives two heterozygous alleles of that gene. But he or she can be a carrier, if has one dominant and one recessive allele of the gene, and can pass it to next generation. As, Robert has the probability to be a carrier, Sandy should go for the test, if they dont want to take any risk for their next generation.
2. Yes, this is helpful. If her ancestors have a defined breast cancer gene abnormality but she tested negative for the abnormality, her risk of breast cancer is considered to be equal to that of a woman in the general population, but risk should not be avoided.
3. Predisposition genetic testing differs from presymptomatic testing in that it informs individuals of an increased or decreased risk of developing the condition in question, but, the degree of certainty is unknown. This sometimes applies to cancer predisposition testing in where a positive result indicates a need for increased surveillance, while a negative result implies a risk similar to the general population but is not negligible. Presymptomatic testing identifies individuals who are expected to become ill in the future. Evaluating a healthy person with a family history of Huntington's disease is an example of presymptomatic genetic testing. Predisposition testing identifies those who are at increased risk of becoming ill, for example, certain mutations in the BRCA1 or BRCA2 genes greatly increase a person's risk of developing breast cancer.
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