Test 163  (Genetics )

1. The following conditions are caused by nondisjunction:

a. phenylketonuria

b. sickle cell disease

c. Down's syndrome

d. Patau's syndrome

e. Edward's syndrome
 

Answera.F   b.F  c.T   d.T   e.T
Nondisjunction refers to failure of two chromosomes 
to separate during meiosis or mitosis resulting in more than the normal number of chromosomes. Trisomy 21 
causes Down's syndrome. Patau's syndrome is caused by trisomy 13 and Edward's syndrome trisomy 18.
 
 

2. The following are true about Turner's syndrome:

a. the patient may be male or female

b. the condition is usually caused by maternal X chromosomal nondisjunction 

c. the incidence of X-linked colour blindness amongst Turner patients is the same as the normal male population

d. it is associated with cataract

e. peripheral retinal pigmentation is a feature
 

Answera.F  b.F  c.T  d.T  e.F
Turner's syndrome (45, XO) affects female with an incidence is 1: 5000 live female birth. The condition is usually caused by paternal X or Y chromosomal nondisjunction. Due to lack of X chromosome, the incidence of colour blindness is the same as that of normal male population. Ocular features include eyelid pigmentation, epicanthal folds, ptosis, strabismus, nystagmus and cataract. Peripheral retinal pigmentation is not a feature.
 
 

3. Karyotype can be obtained from:

a. sperms

b. chorionic villi

c. retinoblastoma cells

d. red blood cells

e. bone marrow cells
 

Answer
a.F   b.T  c.T   d.F  e.T
Karyotype refers to systemic display of chromosomes from a single somatic cell. Sperms are germ cells and normal red blood cells do not contains nucleus.
 

4. The following definitions are correct:

a. syntheny: presence of genes on the same chromosome

b. isochromosome: chromosomes which are identical to each other

c. heteroplasmy: presence of two or more different 
    populations of mitochondria within a cell

d. genoscopy: similar genotypes that manifest as different 
    phenotypes

e. autosome: 23 pairs in normal human beings

Answer
a.T   b.F  c.T  d.F  e.F
Isochromosome refers to an abnormal chromosome 
created by deletion of one arm or duplication of the 
other arm. Genoscopy refers to different nonallelic genotypes that result in a similar phenotype. Autosome refers to chromosomes other than the sex chromosomes there are 22 such pairs in human beings. 
 
 

5. The following techniques are used to directly identify DNA:

a. Western blotting

b. Southern blotting

c. Northern blotting

d. polymerase chain reaction (PCR)

e. denaturing gradient gel electrophoresis
    (DGGE)
 

Answer
a.F   b.T  c.F  d.T  e.T
Western blotting is used to identify proteins whereas Northern blotting is for mRNAs.
.

 

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