Test 7 (genetics)

 
1.  The following are caused by defect in the the mitochondrial DNA:

a. Leigh disease

b. Kearn-Sayer's syndrome

c. myotonic dystrophy

d. Leber congenital amaurosis

e. Leber hereditary optic neuropathy

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Myotonic dystrophy is an autosomal dominant condition whereas Leber congenital amaurosis is an autosomal recessive condition.
 

2. The following are true about mitochondrial DNA:

a. the sperm does not contain mitochondrial DNA

b. it accounts for 10% of total human DNA

c. it encodes protein needed for oxidate phosphorylation

d. defect results in the formation of red ragged muscle

e. the inheritance of mitochondrial disorder is similar to X-linked 
    disorder

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The sperm is rich in mitochondrial DNAs but these DNAs are destroyed soon after fertilization. 
The mitochondrial DNA accounts for 0.5% of total human DNA
Red ragged muscle are muscle fibrils with abnormal mitochondria
The inheritance is maternal and is distinct from X-linked disorders
 

3. Down's syndrome:

a. has an incidence of 1:700

b. is associated with the age of the mothers

c. mosaicism accounts for 2% of all Down's syndrome

d. is more accurately diagnosed in pregnant woman with amiocentesis 
    than hormonal tests

e. is associated with congenital glaucoma
 

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Mosaicism is due to non-disjunction during mitosis in the developing embryo and accounts for 2% of all Down's syndrome. The rest is caused by chromosomal disjunction during meiosis.
It is associated with cataract.
The 'triple test' can be used to detect 60% of Down's syndrome but is not as sensitive as amniocentesis. The triple tests in Down's syndrome show decreased alpha-feto-protein, decreased oestriol and increased human chorionic gonodotrophin.

4. The following are true about the offsprings of a female carrier of an X-linked 
    recessive disorder  and a normal male:

a. half of their children will symptomatic

b. half of their daughters will be symptomatic

c. half of their sons will be asymptomatic carriers

d. half of their daughters will be carriers

e. half of their sons will be symptomatic

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The female will pass the abnormal X chromosome on to half of her daughters who will be carriers. Half of the sons will have the condition as they have a 50% chance of inheriting the X chromosome from the mother. The other half will have normal X chromosome.
 

5. With regard to p53 tumour suppressor gene:

a. it is located on chromosome 17

b. it encodes 53 kDa protein

c. it holds the cell cycle in the G₁ phase

d. it is stimulated by ionizing radiation

e. abnormal gene is associated with childhood tumours

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It arrest the cell cycle in the G₁ phase and allows repair of DNA before mitosis. Its mutation or absence is associated with development of a spectrum of childhood and adult tumours.

6. The following are true about restriction fragment length polymorphisms (RFLPs):

a. they show individual variation

b. they can be used to determine the position of specific genes

c. they are produced by enzymes which cleave DNA at specific sites

d. they can be used for prenatal diagnosis

e. they have not known useful function

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RFLPs are fragments of DNA produced after digestion by enzymes which cleavage the DNA at variable restriction sites.
 

7. Retinoblastoma:

a. is associated with loss of the short arm of chromosome 13

b. is caused by mutation in the growth suppressor gene

c. is an autosomal dominant condition

d. is sporadic in the majority of unilateral cases

e. is inherited in the majority of bilateral cases

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It is associated with loss of the long arm of chromosome 13. 
It appears like an autosomal dominant condition but at the genetic levels both alleles must be affected to produce the disease.
Both unilateral and bilateral cases are sporadic in the majority of cases. 
 

8. In the human cell cycle:

a. cell division occurs in the S phase

b. G₁ precedes mitosis

c. DNA synthesis occurs in G₀

d. vincristine acts on the M phase

e. methotrexate acts on the S phase

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The cell cycle in the human consists of the following sequences: G₁ (first gap) phase, the S (DNA) synthesis phase, G₂  (second gap) phase and the M (mitotic) phase. Cells that suspend their cell cycle are said to be in G₀ (resting) phase.
Methotrexate acts on dihydrofolate reductase and is therefore active at the S phase.
Vincristine acts on protein tubulin which is essential for mitosis and therefore the M phase.
 

9. True statements include:

a. before RNA can be studied by PCR (polymerase chain reaction), it 
    has to be translated into complementary DNA

b.Western blotting  is used to detect specific protein in a mixture of 
    protein

c. Northern blotting is used to detect DNA sequence

d. Southern blotting is primarily used to detect DNA sequence

e. gel electrophoresis is used in both Southern and Northern blottings

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Western blotting for specific protein
Northern blotting for RNA sequence
Southern blotting for DNA sequence.
 

10. The following are true:

a. proto-ongenes regulate the normal cell division

b. mutated proto-oncogenes are associated with cancer

c. gene translocation can transform proto-oncogenes

d. viral insertion can disrupt normal proto-oncogenes

e. ras oncogenes are the most commonly observed oncogenes in 
    human tumours.

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Oncogenes are derived from normal proto-oncogenes. 
The mutation can be brought about by point mutation, viral insertion, gene translocation or gene amplification.
 
 
 

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