UPSC Prelims 2011 · GS Paper I

Question 5: Science and Technology

At present, scientists can determine the arrangement or relative positions of genes or DNA sequences on a chromosome. How does this knowledge benefit us ?

1.It is possible to know the pedigree of livestock.
2.It is possible to understand the causes of all human diseases.
3.It is possible to develop disease-resistant animal breeds.

Which of the statements given above is/are correct ?

a1 and 2 only

b2 only

c1 and 3 only

d1, 2 and 3

AnswerThe answer is (c).

Mapping where genes or DNA sequences lie on a chromosome lets breeders use DNA markers to trace parentage and lineage in livestock, and to locate genes for traits such as disease resistance, which can then be bred into animals. It does not explain the cause of every human disease: many conditions arise from the environment, lifestyle or the interaction of many genes. The word 'all' makes statement 2 an overstatement, so only statements 1 and 3 are correct.

1. DNA markers show parentage and lineage in livestock.
2. Many diseases have environmental or multi-gene causes; 'all' is an overclaim.
3. Genes for resistance can be located and bred into animal stock.

How you could have got this

If you were sure statement 2 is not correct, (a), (b) and (d) go: each of them includes 2.
What you needed to know: Many diseases have environmental or multi-gene causes; 'all' is an overclaim.
The red flag in statement 2 is “all”. In UPSC’s papers, statements with “all” were true 41% of the time (76 statements). A hint, not a rule.

Only (c) is left. You didn’t need statements 1 or 3.

This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.

Which options go is worked out from UPSC’s key and the options, not by a model.

Why each option is right or wrong

(a) Includes statement 2, which claims too much with the word 'all'.
(b) Statement 2 alone is the overclaim, and it excludes the two correct statements.
(c) Right: pedigree tracing and disease-resistant breeds follow from gene mapping.
(d) Statement 2 overstates what gene mapping can explain.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2011, General Studies Paper I, Series A. The paper on upsc.gov.in.