Human Genetics Quiz: Chromosomal Abnormalities

Medical Biology and Genetics: Chromosomal Abnormalities

• Chromosomal abnormalities encompass a range of genetic disorders arising from numerical or structural changes in chromosomes.
• Reference materials used for study include Thompson & Thompson Genetics in Medicine (8th Edition).
• Learning objectives include understanding the genetic basis of numerical and structural syndromes, recognizing clinical features and diagnostic methods, and evaluating treatment options for common syndromes like Down, Turner, and Klinefelter syndromes.

Terminologies

• Aneuploidy: An abnormal number of chromosomes in a cell.
• Trisomy 21 (Down Syndrome): Genetic disorder resulting from an extra copy of chromosome 21.
• Trisomy 18 (Edwards Syndrome): Genetic disorder resulting from an extra copy of chromosome 18.
• Trisomy 13 (Patau Syndrome): Genetic disorder resulting from an extra copy of chromosome 13.
• Uniparental Disomy: A condition where a person inherits two copies of a chromosome from one parent and none from the other.
• Genomic Disorders (Microdeletion and Microduplication Syndromes): Genetic disorders caused by deletions or duplications of small chromosome segments.
• Idiopathic Chromosomal Abnormalities: Chromosomal abnormalities with unknown causes.
• Segregation of Familial Abnormalities: The passing down of chromosomal abnormalities through generations.
• Genomic Imprinting Disorders: Disorders where gene expression differs depending on whether a gene is inherited from the mother or father.
• Hydrops: Swelling of the entire body due to heart failure.
• Micrognathia: Shortness of the lower jaw.
• Microcephaly: Smaller than normal head size.
• Omphalocele: Intestines protruding from an opening in the abdominal wall.
• Polyhydramnios: Excessive amniotic fluid.

Mechanisms of Chromosomal Abnormalities

• Numerical Abnormalities:
  • Polyploidy (multiple chromosome sets)
  • Aneuploidy (abnormal chromosome number)
    • Sex chromosome aneuploidy
    • Autosomal aneuploidy
• Structural Abnormalities:
  • Deletion
  • Duplication
  • Inversion
  • Insertion
  • Ring chromosome
  • Isochromosome
  • Translocations (Robertsonian and Reciprocal)
  • Mosaicism (presence of both normal and abnormal cells)

Structural Chromosomal Abnormalities

• Involving Single Chromosomes:
  • Terminal deletion
  • Interstitial deletion
  • Duplication
  • Inversion
  • Insertion
  • Isochromosome
• Involving Two Chromosomes:
  • Translocations (Robertsonian and Reciprocal)
  • Ring chromosome

Polyploidy

• Autopolyploidy: Increase in chromosome sets within a species.
• Allopolyploidy: Increase in chromosome number due to hybridization between closely related species.
• Mechanisms of Polyploidy:
  • Anaphase Lag
  • Endoreduplication
  • Failure of cytokinesis

Triploidy

• Triploidy is a chromosomal abnormality characterized by the presence of three sets of chromosomes (69 for humans).
• Most cases result in spontaneous abortion.
• Triploidy typically results from dispermy or errors in meiosis leading to a diploid egg.

Aneuploidy

• Aneuploidy is a condition with an abnormal number of chromosomes either missing or extra copies.
• Examples: Trisomy (extra copy of a chromosome), Monosomy (missing a copy of a chromosome).
• Types: Partial and Mosaic (variations in the proportion of normal/abnormal cells).

Trisomic and Other Common Syndromes

• Trisomy 21 (Down Syndrome): Significant incidence, distinct clinical features (hypotonia, facial features, intellectual disability).
• Trisomy 18 (Edwards Syndrome): Severe developmental problems, low survival rates.
• Trisomy 13 (Patau Syndrome): Similar to Trisomy 18 in severity, low survival rates.
• Other Syndromes: Klinefelter Syndrome (extra X chromosome in males), Turner Syndrome (missing or incomplete X chromosome in females), Cri du Chat Syndrome (deletion of chromosome 5), Wolf-Hirschhorn Syndrome (deletion of chromosome 4).

Mechanisms of Chromosomal Abnormalities (Summary)

• Segregation Errors: Nondisjunction (failure of homologous or sister chromatids to separate properly during meiosis) and Anaphase Lagging.
• Chromosomal Rearrangements: Deletions, duplications, inversions, and translocations (structural alterations).

Risk Factors and Diagnostics

• Maternal age is a primary risk factor for certain chromosomal abnormalities.
• Prenatal diagnostics like karyotype, chromosomal microarray analysis, and non-invasive prenatal screening aid in diagnosis.
• Factors like the parents' karyotypes also influence the risk for recurrent abnormalities.

Additional Syndromes and Anomalies

• Deletions: 1p36 deletion syndrome, Cri du Chat Syndrome, 4p-deletion syndrome (Wolf-Hirschhorn Syndrome).
• Duplications: Various duplications of chromosomal regions exist.
• Isochromosomes: Abnormal chromosomes, consisting of two copies of a single (either p or q) arm.
• Ring Chromosomes: Abnormal chromosomes, resulting from the fusion of broken ends.

Further Study/References

• Specific details of individual syndromes and their associated characteristics, treatment approaches, and recurrence risks should be reviewed from appropriate sources (like the referenced textbook mentioned earlier).