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Questions and Answers
What is characterized by an interstitial deletion in the short arm of chromosome 5?
What is characterized by an interstitial deletion in the short arm of chromosome 5?
Which type of chromosomal rearrangement leads to a change in the centromere index?
Which type of chromosomal rearrangement leads to a change in the centromere index?
What structural aberration is described as the reattachment of a chromosome segment to a different chromosome?
What structural aberration is described as the reattachment of a chromosome segment to a different chromosome?
What is the clinical feature most commonly associated with Cri du chat syndrome in newborns?
What is the clinical feature most commonly associated with Cri du chat syndrome in newborns?
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Which of the following structural aberrations is identified as the most frequent, occurring in 1 out of every 1000 newborns?
Which of the following structural aberrations is identified as the most frequent, occurring in 1 out of every 1000 newborns?
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Which structural chromosomal aberration is characterized by a gain of genetic material followed by a chromosome break and healing?
Which structural chromosomal aberration is characterized by a gain of genetic material followed by a chromosome break and healing?
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What describes the clinical significance of structural chromosomal aberrations?
What describes the clinical significance of structural chromosomal aberrations?
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Which notation describes a chromosomal deletion in the karyotype notation format?
Which notation describes a chromosomal deletion in the karyotype notation format?
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What is the result of a translocation between two chromosomes?
What is the result of a translocation between two chromosomes?
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Which of the following correctly identifies an isochromosome?
Which of the following correctly identifies an isochromosome?
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Study Notes
Structural Chromosomal Aberrations
- Structural chromosomal aberrations are abnormalities in the structure of chromosomes, specifically structural rearrangements or mutations of chromosomes.
- Causes include radiation, viruses, drugs, and insecticides.
Types of Structural Aberrations
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Intrachromosomal aberrations: These aberrations occur within a single chromosome.
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Breaks: Relatively common, involving simple breakage followed by rapid healing of the broken ends.
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Deletion: Partial monosomy, caused by loss of a segment of a chromosome due to breaks. Can be terminal (one break) or interstitial (two breaks).
- Examples: Wolf syndrome, Cri du chat syndrome.
- A terminal deletion involves the loss of a chromosome tip, usually containing telomeres.
- An interstitial deletion results from a break within a chromosome arm, leading to the loss of a segment between the breakpoints.
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Ring chromosome: Two terminal breaks on the same chromosome, resulting in a circular arrangement, usually with deletion of the telomeres.
- Loss of part of the chromosome, potentially affecting genes.
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Inversion: A segment of a chromosome reverses its orientation and reattaches to the same chromosome. Classified as paracentric (segment inversion excludes the centromere) or pericentric (segment inversion includes the centromere).
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Duplication: Partial trisomy, which is the presence of extra copies of a particular chromosome segment or the entire chromosome. Caused by replication errors or unequal crossing over between homologous chromosomes.
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Interchromosomal aberrations: These aberrations occur between different chromosomes.
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Translocation: A part of one chromosome breaks off and attaches to a different, non-homologous chromosome. Can be reciprocal (no gain or loss of genetic information) or Robertsonian (fusion of two whole arms ending in a single chromosome, often involving acrocentric chromosomes).
- Examples: Philadelphia chromosome (Ch 22 & 9 translocation), Down syndrome (translocation variant).
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Insertion: Structural chromosomal rearrangement involving 3 breaks in two different (heterologous) chromosomes. One segment is deleted from one chromosome and added to another.
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Isochromosome: An unbalanced structural abnormality. Formed by the misdivision of a chromosome's centromere, resulting in two identical arms.
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Karyotype Symbols
- p: Short arm of a chromosome.
- q: Long arm of a chromosome.
- cen: Centromere.
- del: Deletion.
- dup: Duplication.
- fra: Fragile site.
- i: Isochromosome.
- inv: Inversion.
- ish: In-situ hybridization.
- r: Ring.
- t: Translocation.
- ter: Terminal or end.
- + or -: Indicate gain or loss of part of that chromosome, in relation to the normal karyotype.
Clinical Features of Cri du Chat Syndrome
- High-pitched cry (like a cat), common in newborn babies.
- Ear malformations.
- Broad and depressed (flat) nose.
- Widely set, slanting eyes.
- Small receding mandible.
- Small head.
- Heart defects
- Mental Retardation
- Facial defects
- Small head and low birth weight.
Specific Diseases related to chromosomal anomalies
- Down Syndrome: Caused by an extra copy of chromosome 21 (trisomy). Causes a variety of developmental issues.
Case Study Summaries
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Case 1: A 10-year-old girl with short stature, low-set ears, low posterior hairline, and streak ovaries suggests Turner syndrome. XO is the diagnosis.
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Case 2: A 28-year-old man with infertility, tall stature, and feminine hair distribution, and enlarged breasts suggests a possible sex chromosome abnormality, like Klinefelter syndrome (47, XXY).
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Case 3: A 40-year-old pregnant woman with a newborn having umbilical cord knots and a weak mewing cat-like cry suggests Cri du chat syndrome.
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Mechanism of chromosomal anomalies: Different mechanisms (including X-ray exposure) can cause structural chromosomal alterations such as inversion, deletion, duplication, translocation, etc. This can lead to abnormalities.
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Description
Explore the various types of structural chromosomal aberrations and their causes. This quiz covers intrachromosomal aberrations, including breaks, deletions, and ring chromosomes. Learn about the implications and examples of these abnormalities in human genetics.
