Name_________________________
For this take-home portion use your notes as well as any other resources (classmates, internet, library etc.). However, turn in your own work!
1. Chromosomal analysis of chorionic villus sample reveals Trisomy 15. A subsequent amniotic fluid sample reveals cells with normal karyotype. Explain how this discrepancy could occur. If a live birth occurs from this pregnancy are there any potential complications that would be expected based on the findings of the chromosome analysis?
This discrepancy could occur by chromosomal mosaicism and mitotic non-disjunction. Other changes in the number or structure of chromosome 15 can cause mental retardation, delayed growth and development, hypotonia, and characteristic facial features.
2. A test based on a molecular probe for SRY was used to ensure that potential competitors for the women’s Olympic events in Atlanta had no SRY gene. Explain what this test was attempting to determine. How could it be that a woman could have the SRY gene? In your answer you should include the relevant chromosomal genotype of a woman with the SRY gene as well as a description of her “gonadal phenotype”.
This test was used to determine if a competitor was actually a woman; however, the test also excluded people with androgen insensitivity, which is where a person has a XY genotype, yet is phenoypically a female. Because of the mutation in an X0linked gene called the androgen receptor, no testosterone receptors are produced, and cells can’t respond to testosterone or DHT. The genitalia develops as a female even though they are genetically a male. A person with Androgen Insensitivity does not menstruate and have well-developed breasts and very little pubic hair.
3. What are the most common phenotypic features associated with Turner Syndrome? What is the difference between a woman with 45, X and one with 46, XX given that in all of the cells of a 46, XX individual one X chromosome is inacitivated?
The most common phenotypic features associated with Turners Syndrome are short and wide-chested females with rudimentary ovaries. When born, infants with Turners have puffy hands and feet, but this disappears after infancy.
4. One study estimated that approximately 30% of Turner patients have a 45, X karyotype (Fernandez et al., 1996) and the remainder are mosics of 45, X cells and cells containing a second sex chromosome. This is usually an X chromosome (ie. 45, X/46, XX mosaic), but in about 6-12% of the cases, a second cell line containing a Y chromosome is present (ie. 45, X/46, XY mosaic). Explain how these individuals with chromosomal mosaic, Turner Syndrome could come to be. How are they different from Turner patients with 45, X karyotype? Based on what you know about the Y chromosome, what differences would you predict to find between a 45, X/46, XX mosaic and a 45, X/46, XY mosaic?
Extra Credit:
5. A lady I work with (Sandy) recently asked me if cancer is genetically inherited. This is a very open ended question isn’t it!!!! This is a common question that all of you should leave this class feeling as though you can answer this. Now that you have completed Bio 355, what would you tell Sandy? Be specific in your answer. Make a few general points and back each of them up with an example. Your notes should go a long way in answering this question.
I would tell Sandy that it depends on a few things. The first would be environmental factors such as weather, climate, diet, and residence (such as urban or rural). The second would be your genetic makeup.
1. Chromosomal analysis of chorionic villus sample reveals Trisomy 15. A subsequent amniotic fluid sample reveals cells with normal karyotype. Explain how this discrepancy could occur. If a live birth occurs from this pregnancy are there any potential complications that would be expected based on the findings of the chromosome analysis?
This discrepancy could occur by chromosomal mosaicism and mitotic non-disjunction. Other changes in the number or structure of chromosome 15 can cause mental retardation, delayed growth and development, hypotonia, and characteristic facial features.
2. A test based on a molecular probe for SRY was used to ensure that potential competitors for the women’s Olympic events in Atlanta had no SRY gene. Explain what this test was attempting to determine. How could it be that a woman could have the SRY gene? In your answer you should include the relevant chromosomal genotype of a woman with the SRY gene as well as a description of her “gonadal phenotype”.
This test was used to determine if a competitor was actually a woman; however, the test also excluded people with androgen insensitivity, which is where a person has a XY genotype, yet is phenoypically a female. Because of the mutation in an X0linked gene called the androgen receptor, no testosterone receptors are produced, and cells can’t respond to testosterone or DHT. The genitalia develops as a female even though they are genetically a male. A person with Androgen Insensitivity does not menstruate and have well-developed breasts and very little pubic hair.
3. What are the most common phenotypic features associated with Turner Syndrome? What is the difference between a woman with 45, X and one with 46, XX given that in all of the cells of a 46, XX individual one X chromosome is inacitivated?
The most common phenotypic features associated with Turners Syndrome are short and wide-chested females with rudimentary ovaries. When born, infants with Turners have puffy hands and feet, but this disappears after infancy..
4. A lady I work with (Sandy) recently asked me if cancer is genetically inherited. This is a very open ended question isn’t it!!!! This is a common question that all of you should leave this class feeling as though you can answer this. Now that you have completed Bio 355, what would you tell Sandy? Be specific in your answer. Make a few general points and back each of them up with an example. Your notes should go a long way in answering this question.
I would tell Sandy that it depends on a few things. The first would be environmental factors such as weather, climate, diet, and residence (such as urban or rural). The second would be your genetic makeup.
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