Examkin

Question

Difficulty: HardGene Mutations and Chromosomal Aberrations

In a molecular genetics analysis of a patient, a single nucleotide substitution is detected where adenine is replaced by thymine in the sixth codon of the β\beta-globin gene, causing glutamic acid to be replaced by valine. Which of the following correctly classifies this genetic change and the pattern of variation its resulting phenotype displays in human populations?

  1. A gene mutation resulting in discontinuous variationAnswer
  2. B
    A gene mutation resulting in continuous variation
  3. C
    A sex-linked chromosomal aberration resulting in discontinuous variation
  4. D
    A somatic chromosomal aberration inherited via environmental adaptation

Answer

The genetic change is classified as a gene mutation and the resulting phenotype displays discontinuous variation.
The substitution of a single nitrogenous base in a codon alters the amino acid sequence of a specific polypeptide without altering the macroscopic structure or number of chromosomes, defining it as a gene (point) mutation. Because the resulting sickle-cell condition produces distinct, clear-cut phenotypic classes (normal, carrier, affected) without intermediate continuum states, it represents discontinuous variation.

Step-by-Step Solution

1
Classify the type of genetic modification
Replacing a single nucleotide base (adenine with thymine) within the coding sequence of the β\beta-globin gene constitutes a point mutation (gene mutation), as it affects only the nucleotide sequence of one gene without altering chromosome structure or number.
Gene mutations involve localized alterations in the DNA base sequence of a single gene locus.
2
Determine the resulting pattern of genetic variation
Sickle-cell trait/anemia displays distinct, non-overlapping phenotypic categories (unaffected, sickle-cell trait carrier, or sickle-cell anemia).
Traits governed by single gene loci with clear discrete phenotypic classes exemplify discontinuous variation.

Key Concept

Gene mutation vs chromosomal aberration and its phenotypic expression as discontinuous variation
Estimated Time:2m 0s
Rate this question

Topics

Gene Mutations and Chromosomal Aberrations

More questions from this topic