20 Questions
What is the main cause of structural chromosomal abnormalities?
Viral infections
What is the result of unbalanced chromosomal rearrangement?
Severe clinical effects
What is the characteristic of balanced chromosomal rearrangement?
It is usually harmless
What is the result of deletion of a short arm of chromosome 5?
Cri-du-Chat syndrome
What is the technique used to detect micro-deletion?
FISH
What is the condition characterized by underdevelopment of the larynx and a characteristic cat-like cry?
Cri-du-Chat syndrome
What is the type of inversion that involves both p and q arms?
Pericentric inversion
What is the indication for routine chromosome investigation?
All of the above
What is the result of terminal deletion of a chromosome?
Monosomy
What is the type of structural chromosomal abnormality that results in extra copies of a chromosome part?
Duplication
What is the result of a paracentric inversion?
A segment of one arm is involved and inverted.
What is the characteristic of a ring chromosome?
Loss of telomeres or ends of both arms of a chromosome.
What is the result of an isochromosome?
Creation of two non-identical chromosomes.
What is the result of an insertion?
Rearrangement of genetic material to a non-homologous chromosome.
What is the characteristic of a reciprocal translocation?
Rearrangement of genetic material between two non-homologous chromosomes.
What is the result of a Robertsonian translocation?
Rearrangement of genetic material between two acrocentric chromosomes.
What is the notation for a normal female karyotype?
46,XX
What is the notation for a deletion of a segment on the short arm of chromosome 5?
46,X,5p-
What is the characteristic of balanced structural abnormalities?
May result in a loss or gain of genetic material.
What is the characteristic of unbalanced structural abnormalities?
Always result in a loss of genetic material.
Study Notes
Chromosomal Abnormalities
- Chromosomal abnormalities result from breakage and incorrect rejoining of chromosomal segments, leading to disease.
- Environmental factors responsible for structural abnormalities include: • Ionizing radiation • Ultraviolet light • Chemical agents • Viral infections
Indications for Chromosome Investigation
- Prenatal screening: • Down's syndrome, especially in cases of advanced maternal age (>35 years) or family history of chromosome abnormality • Abnormal ultrasound scan of fetus
- Birth defects: • Malformations • Mental retardation
- Abnormal sexual development (e.g., Klinefelter's syndrome)
- Infertility
- Recurrent fetal loss
Types of Structural Chromosomal Abnormalities
- Balanced rearrangements: • Exchange or rearrangement of genetic material without loss or gain of genetic material • Generally harmless, but carriers are at risk of producing children with unbalanced chromosomal complement
- Unbalanced rearrangements: • Incorrect amount of chromosomal material, resulting in severe clinical effects
Deletions
- Loss of genetic material, resulting in monosomy for the segment of the chromosome
- Types of deletions: • Terminal deletion: involves a single break of the terminal part of the chromosome • Interstitial deletion: involves two breaks and loss of the intervening portion of the chromosome
- Example: Cri-du-Chat syndrome (46,XX,5p- or 46,XY,5p-)
Duplications
- Extra copies of a chromosome part
Inversions
- Involves two breaks along the chromosome, resulting in a reversal of a segment
- Types of inversions: • Pericentric inversion: involves both p and q arms with centromere • Paracentric inversion: involves only one arm
Ring Chromosomes
- Loss of telomeres or ends of both arms of a chromosome, forming a ring structure
Isochromosomes
- Creation of two non-identical chromosomes, one with a combination of short arms, the other with a combination of long arms
Insertions
- Rearrangement of genetic material to a non-homologous chromosome, without loss of genetic material
Translocations
- Exchange of genetic material between two chromosomes
- Types of translocations: • Reciprocal translocation: no loss of genetic material, but an exchange of genetic material between two non-homologous chromosomes • Robertsonian translocation (centric fusion): involves break at or near the centromere in two acrocentric chromosomes and subsequent fusion of their long arms
Karyotype Nomenclature
- Normal female or male: 46,XX or 46,XY
- Extra or missing entire chromosome: e.g., 47,XX,+21 or 45,XX,-15
- Missing piece of a chromosome: e.g., 5p-
- Other notations include: • del (deletion) • dup (duplication) • inv (inversion) • ins (insertion) • rob (Robertsonian translocation) • t (translocation)
A lecture on chromosomal abnormalities, specifically structural abnormalities, covering topics such as breakage and reunion events. Presented by Dr. Dhamyaa K. Kadhim.
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