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Difficulty: MediumGene Mutations and Chromosomal Aberrations

In human genetics, sickle-cell anaemia and Down syndrome represent two distinct types of genetic disorders. Which of the following statements correctly differentiates between the underlying genetic causes of these two conditions?

  1. Sickle-cell anaemia is caused by a point mutation in a single gene, whereas Down syndrome is caused by a chromosomal numerical aberration.Answer
  2. B
    Sickle-cell anaemia is caused by chromosomal non-disjunction, whereas Down syndrome is caused by a base substitution mutation.
  3. C
    Both conditions are caused by structural chromosomal aberrations occurring during crossing over.
  4. D
    Both conditions are caused by point mutations that exhibit continuous variation in human populations.

Answer

Sickle-cell anaemia is caused by a point mutation in a single gene, whereas Down syndrome is caused by a chromosomal numerical aberration.
The correct response accurately distinguishes the scope of the genetic error. Sickle-cell anaemia is a classic gene mutation resulting from a single point substitution in the DNA sequence coding for beta-globin. Down syndrome is a chromosomal numerical aberration (aneuploidy/trisomy 21) resulting from the failure of chromosome pair 21 to separate during gamete formation (non-disjunction).

Step-by-Step Solution

1
Analyze the cause of sickle-cell anaemia
Determined that sickle-cell anaemia is a gene mutation caused by a single nucleotide substitution (GAG to GUG) in the hemoglobin gene.
Gene mutations involve alterations in the molecular sequence of nucleotides within a single gene.
2
Analyze the cause of Down syndrome
Determined that Down syndrome is a chromosomal aberration involving an extra chromosome 21 (trisomy 21) caused by non-disjunction during meiosis.
Chromosomal aberrations involve changes in the number or gross structure of whole chromosomes rather than single nucleotide changes.
3
Compare the classifications
Matched sickle-cell anaemia to gene mutation and Down syndrome to chromosomal numerical aberration.
This establishes the fundamental distinction between point gene mutations and numerical chromosomal abnormalities.

Key Concept

Distinction between Gene Mutations and Chromosomal Aberrations
Estimated Time:1m 0s
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Topics

Gene Mutations and Chromosomal Aberrations

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