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Sickle cell anemia is the clinical manifestation of homozygous genes

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asked Oct 16, 2016 in Biochemistry by Rajesh Bahara
Sickle cell anemia is the clinical manifestation of homozygous genes for an abnormal hemoglobin molecule. The mutation in the β chain is known to produce a single amino acid change. The most likely mechanism for this mutation is?

a. Crossing over
b. Two-base insertion
c. Three-base deletion
d. Nondisjunction
e. Single-base substitution (point mutation)

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Best answer
The answer is e.
e. Single-base substitution (point mutation)

(Murray, pp 412–434. Scriver, pp 3–45. Sack, pp 3–29. Wilson, pp 99–121.) In the β-globin chain of hemoglobin S (141900), a valine residue replaces a glutamic acid at the sixth amino acid position from the N-terminus. The amino acid substitution is the result of a single- base change (point mutation) from thymine to adenine at the second position of the sixth codon. Crossing over among homologous β-globin genes might exchange alleles, if equal, or generate mutant alleles with duplicated/deficient nucleotides, if unequal. Two-base insertions would change the reading frame of the genetic code (frame-shift mutation) and produce a nonsense peptide after the point of insertion. Three-base deletions could also cause frame shifts or, if one codon were removed, delete one amino acid. Nondisjunction involves abnormal segregation of chromosomes at meiosis or mitosis, and would produce nonviable individuals or somatic cells with additional or missing copies of chromosome 11 and its β-globin locus.
answered Oct 16, 2016 by Rajesh Bahara

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