Examkin

Question

Difficulty: MediumGene Mutations and Chromosomal Aberrations

A cytogenetic analysis of a patient reveals a somatic cell chromosomal complement of 4747 chromosomes with an additional sex chromosome (47,XXY47, XXY). Which mechanism is directly responsible for this structural or numerical chromosomal aberration, and what clinical condition does it produce?

  1. Nondisjunction of sex chromosomes during meiotic division, resulting in Klinefelter syndromeAnswer
  2. B
    Single nucleotide base substitution in a gene coding sequence, resulting in Sickle cell anaemia
  3. C
    Reciprocal translocation between autosomes during somatic mitosis, resulting in Down syndrome
  4. D
    Frameshift deletion mutation in an X-linked recessive allele, resulting in Haemophilia

Answer

Nondisjunction of sex chromosomes during meiotic division, resulting in Klinefelter syndrome
The correct option correctly attributes the karyotype 47,XXY47, XXY to nondisjunction during gametogenesis. When pair 23 fails to disjoin properly during meiosis, an egg carrying XXXX fertilized by a YY sperm (or an XX egg fertilized by an XYXY sperm) produces an individual with 4747 chromosomes (47,XXY47, XXY), which manifests as Klinefelter syndrome.

Step-by-Step Solution

1
Analyze the given karyotype
The individual has 4747 chromosomes including an extra X chromosome (47,XXY47, XXY).
Normal human somatic cells have 4646 chromosomes (4444 autosomes + 22 sex chromosomes).
2
Identify the genetic mechanism leading to gain of a whole chromosome
The mechanism is meiotic nondisjunction, where chromosomes fail to separate properly during Anaphase I or II.
Gene mutations (substitutions, insertions, deletions) alter nucleotide sequences within a single gene but do not change the total number of chromosomes.
3
Match karyotype 47,XXY47, XXY to its clinical condition
An extra X chromosome in a male (47,XXY47, XXY) causes Klinefelter syndrome.
Trisomy 21 causes Down syndrome, whereas sex-chromosome trisomy 47,XXY47, XXY defines Klinefelter syndrome.

Key Concept

Chromosomal Aberrations and Nondisjunction
Estimated Time:1m 0s
Rate this question

Topics

Gene Mutations and Chromosomal Aberrations

More questions from this topic