Sickle-cell anaemia is (2009)

(A)caused by substitution of valine by glutamic acid in the beta globin chain of haemoglobin
(B)caused by a change in a single base pair of DNA
(C)characterized by elongated sickle like RBCs with a nucleus
(D)an autosomal linked dominant trait

The NCERT line that answers it

Verbatim line

The substitution of amino acid in the globin protein results due to the single base substitution at the sixth codon of the beta globin gene from GAG to GUG.

Chapter: Principles of Inheritance and Variation
Section: 4.8.2 Mendelian Disorders
Page: 24
Words matched: 29 of 29

The answer appears as a continuous sentence in NCERT. This is that sentence.

How this line gives the answer

0, emb=1.0, combined=1.0). Verified: high — The span explicitly states 'single base substitution at the sixth codon of the beta globin gene', which directly matches option B's claim that sickle-cell anaemia is 'caused by a change in a single base pair of DNA'.

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