A male patient age 15 comes into your clinic presenting the symptoms of mental r

Question

A male patient age 15 comes into your clinic presenting the symptoms of mental retardation, behavioral abnormalities, including hand flapping and hyperactivity. Additionally, you notice this patient has some facial abnormalities, including large ears and a prominent jaw and forehead. Due to the mental retardation, you initially suspect that this disorder may be a trisomy of chromosome 21.

1. (2 points) Is trisomy 21 a chromosomal or single gene disorder? Please explain why.

2. (3 points) Please describe an experimental technique you could use to determine whether the patient has trisomy 21. Include in your description, what the experimental result would be if he did have trisomy 21, or he did not?

After performing the technique you described in question 2, you find out that he did not have the trisomy 21. You next ask the family if there are other members afflicted with the disorder and the answer is yes. Afterward, you get a full family history and put it together to form a pedigree.

After realizing that this is a single gene disorder, you believe the patient is suffering from Fragile X Syndrome. Answer the following questions below based on Fragile X syndrome.

4. (1 point) What gene is affected in Fragile X syndrome?

5. (1 point) Please create a list of symptoms a Fragile X patient may have?

6. (2 points) Based on the symptoms above, please discuss briefly why you may have been initially tricked into thinking this disorder was a chromosomal disorder.

7. (1 point) Please go to page 262 in your book, and explain in detail the nature of the mutation that causes Fragile X syndrome.

8. (2 points) Of the two techniques listed below, which would best allow you to state whether the patient has Fragile X syndrome? Please explain your answer.

a. PCR

b. RFLP

9. (2 points) Please answer question 9 using the information from questions 7 and 8. You analyze your data from the PCR reaction from question 8, which amplifies the region were the insertion lies. You notice that the patient’s sister has a single band on the gel at 45 base pairs. You notice the mother has a band at 200 base pairs and a band at 45 base pairs. The patient has a single band on the gel at 200 base pairs, and the father has a single band at 45 base pairs.

a. What is the genotype of the father and what is the phenotype of the sister?

b. Based on the experiment, what is the size of the insertion region in the wild-type allele, and what is the size of the insertion region in the mutant allele?

c. What is the actual size of the insertion (Hint: think about the difference in the sizes of the insertion region)

Explanation / Answer

1. trisomy is a chromosomal disorder where a part of different chromosome comes and lie adjacent to chromosome 21 leaading to a situation of trisomy. this disorder does not pass to next generation.

2. we can detect trisomy by isolating some somatic cells from the body then staining the cell with saffranine and viewing under microscope at metaphase stage. At this stage try to locate chromosome 21, instead of 2 sets of chromosome u will see an extra strech of chromosome lying adjacent to this chromosome if that person is suffering from trisomy.

4. in this disorder FMR1 gene present on X-chromosome gets mutated so that a CGG repeat get accumulated several times due to replication slippage. Normaly CGG repaeat occurs ~40 timeS but in this disorder this repeat occurs more than 200 times.

5. symptoms: large ear, big face, soft skin, arched palate, low muscle tone.

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