A partial DNA sequence for normal hemoglobin and a partial DNA sequence for sickle-cell anemia are shown below. G-G-A-C-T-T-C-T-T Normal hemoglobin G-G-A-C-A-T-C-T-T Sickle-cell anemia Based on the DNA sequences, sickle-cell anemia is caused by A. a sex-linked trait. B. a dominant nucleotide. C. a mutation in the genetic code. D. an incomplete separation of chromosomes.

C. a mutation in the genetic code.

Explanation:

A mutation refers to any change or alteration to the nucleotide sequence of a gene caused by mutagen or mistakes during replication. Depending on the manner of occurrence, mutation can be of different types. In this question, partial DNA sequence for normal hemoglobin is given as: G-G-A-C-T-T-C-T-T while the partial DNA sequence for sickle cell anaemia is given as: G-G-A-C-A-T-C-T-T.

From careful observation of the two two DNA sequences above, it can be realized that a SUBSTITUTION MUTATION from T to A has occurred in the sequence of sickle cell. Note that substitution mutation is the replacement of one base by another in a sequence.

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