1. A series of three nucleotides on a gene that encodes a protein is called:
A) Intron
B) Exon
C) Codon
D) Messenger RNA
2. Antibiotic resistance in bacteria is genetically transmitted through:
A) Chromatid
B) Chromosome
C) Plasmid
D) Centrioles
3. Chromosomal makeup in Turner syndrome is:
A) 45XO
B) 45XX
C) 46XX
D) 46XXX
4. A newborn female child presenting with hypoplastic left heart syndrome was found to have 45XO chromosomes. The diagnosis is:
A) Klinefelter syndrome
B) Down’s syndrome
C) Turner syndrome
D) Robertsonian translocations
5. All of the following are single gene disorders except:
A) Klinefelter syndrome
B) Marfan syndrome
C) Cystic fibrosis
D) Hemophilia
6. Choose an option that does not represent chromosomal disorder:
A) Klinefelter syndrome
B) Down Syndrome
C) Turner syndrome
D) Duchenne muscular dystrophy
7. All of the following conditions represent autosomal recessive inheritance EXCEPT:
A) Sickle cell anemia
B) Cystic fibrosis
C) Haemophilia
D) Phenylketonuria
8. What is the most common viable aneuploidy (abnormal number of chromosomes) in humans?
A) Klinefelter syndrome
B) Down syndrome
C) Edwards syndrome
D) Turner syndrome
9. The commonest mechanism of genetic abnormality in a case of Trisomy 21 is:
A) Nondysjunction in maternal gamete
B) Nondysjunction in paternal gamete
C) Translocation to chromosome 14
D) Translocation to any autosome
10. Chorionoc villus sampling is done at what gestation?
A) 6-9 weeks
B) 10-12 weeks
C) 14-20 weeks
D) 14-28 weeks
Answers:
Ans: 1- C
Genetic code is represented by codons, which are a series of three nucleotides. The code specifies the amino acid to be added next, in the process of protein synthesis. Messenger RNA is the RNA that conveys genetic information from DNA to ribosomes. When a messenger RNA is synthesised, exons (nucleotide sequence encoded by gene) become part of mature messenger RNA, whereas introns are spliced away.
Ans: 2-C
A plasmid is DNA material separate from chromosomal DNA. The plasmid DNA can be transmitted by horizontal gene transfer to bacteria of same or other species. This is the mechanism of antibiotic resistance in bacteria.
ANS: 3-A
Turner syndrome is also known as monosomy X, as one of the X chromosome is missing from all cells or from some cells (mosaicism). Characteristic features of turner syndrome are; Short stature, low hair line, low set ears and webbed neck.
Ans: 4- C
45XO represents monosomy X or Turner syndrome. Most commonly observed congenital heart disease are obstructive lesions of the left side of the heart including coarctation of aorta, bicuspid aortic valve and hypoplastic left heart syndrome.
Ans: 5-A
Klinefelter syndrome is a chromosomal disorder in which there is at least one extra X chromosome in the genetic makeup. Thus it is known as the chromosomal disorder and is not a single gene mutation.
Ans: 6- D
Duchenne muscular dystrophy is X- linked recessive condition.
Ans: 7- C
Haemophilia is recessive disorder of X- chromosome. Males are affected more frequently than females. Mothers are carriers. Others are autosomal recessive disorders.
Ans: 8- B
Down syndrome ( Trisomy 21) is the most common autosomal aneuploidy that the infant can servive with. Klinefelter syndrome (at least one extra X chromosome) is the most common sex chromosome aneuploidy. Most cases of Turner syndrome (Monosomy X) result in abortions. Edwards syndrome (trisomy 18) is rare.
Ans: 9- A
Trisomy 21 is caused by a meiotic nondysjunction event most commonly in the ovum. The affected ovum has 24 chromosomes with an extra copy of chromosome 21. When it combines with a normal sperm, the embryo has 47 chromosomes with trisomy 21. Mechanisms mentioned in other options are less common causes of Down syndrome.
Ans: 10- B
Chorionic villus sampling is done after 9 weeks of gestation till 12.5 weeks of gestation. Amniocentesis can be done from about 14 weeks till 20weeks.
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