Sunday, 13 December 2015

Frequently Asked Genetics Objective Type Questions And Answers

21- The parents of a child with cystic fibrosis consult you wishing to know what is the risk of their next child being a carrier of the condition. Which ONE of the following percentages is the correct risk?
1) 0%
2) 25%
3) 50%
4) 75%
5) 100%
As both parents are carriers for the CF gene then the chances of another child being affected (homozygote) is 1 in 4 (25%). The chances of their child being free
from the CF gene is also 1 in 4 (25%) and the chances of a child being a carrier (heterozygote) is 1in 2 (50%).

22- Which of the following is NOT true regarding the polymerase chain reaction:
1) It is used to amplify DNA but not RNA
2) The amount of DNA required makes it unsuitable for early prenatal diagnosis
3) Synthetic short DNA primers which flank the sequence of interest are required to initiate the amplification
4) It utilizes the thermostable properties of Taq DNA polymerase
5) It can be used to detect the presence of viral DNA in human disease
rt-PCR is used to amplify RNA rather than PCR specifically. Preimplantation diagnosis uses IVF and genetic analysis of 3 day old embryos, before selective
transfer of unaffected embryos to uterus.

23- The Polymerase Chain Reaction (PCR) is used to amplify small amounts of DNA for further analysis. First the DNA double helix must be split into two strands. This is achieved by
1) alkali solution
2) centrifugation
3) DNA polymerase
4) heating to nearly 100°C
5) viral reverse transcriptase

24- Protein synthesis occurs within cells. A particular molecule that is produced in the nucleus initiates protein synthesis. This molecule matures in the cytoplasm and binds to the ribosome. This molecule is
1) messenger RNA
2) ribosomal RNA
3) RNA nucleotide
4) RNA polymerase
5) transfer RNA

25- A 17-year-old girl is short in stature for her age. She has not shown any changes of puberty. She has a webbed neck. Her vital signs include Temperature 36.6°C Respiratory rate 18/min Pulse 75 bpm and BP 165/85 mmHg. On physical examination, she has a continuous murmur heard over both the front of the chest as well as her back. Her lower extremities are cool with poor capillary filling. A chest radiograph reveals a prominent left heart border, no oedema or effusions, and rib
notching. Which of the following pathologic lesions best explains these findings?
1) Constriction of the aorta past the ductus arteriosus
2) Lack of development of the spiral septum and partial absence of conus musculature
3) Shortening and thickening of chordae tendineae of the mitral valve
4) Single large atrioventricular valve
5) Supravalvular narrowing in the aortic root
She has coarctation of the aorta, and the constriction is postductal, allowing prolonged survival. Her physical characteristics also suggest Turner syndrome
(monosomy X).

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