Chromosomes and Chromosomal Abnormalities Flashcards
What are three key features used to recognise chromosomes?
Banding pattern, length, and centromere position.
What are the arms of a chromosome called?
Short arm: p, Long arm: q.
What is the function of telomeres?
They protect chromosome ends from deterioration or fusion with neighboring chromosomes.
What are acrocentric chromosomes, and why are they significant?
Chromosomes with very short p arms, usually carrying ribosomal RNA genes. Examples: 13, 14, 15, 21, 22.
How many chromosomes are in a normal human karyotype?
46 chromosomes (23 pairs), e.g., 46,XX or 46,XY.
What is the difference between balanced and unbalanced chromosomal rearrangements?
Balanced: All chromosomal material is present;
Unbalanced: Extra or missing chromosomal segments.
What is aneuploidy?
The presence of an abnormal number of chromosomes (e.g., 45 or 47 instead of 46).
Name three common autosomal trisomies and their associated syndromes.
Trisomy 21: Down syndrome
Trisomy 18: Edward syndrome
Trisomy 13: Patau syndrome
Give examples of X chromosome aneuploidy.
45,X: Turner syndrome
47,XXX: Triple X
47,XXY: Klinefelter syndrome
What is a Robertsonian translocation?
Fusion of two acrocentric chromosomes, often 14 and 21, which can lead to trisomies.
What are reciprocal translocations?
Exchange of segments between two nonhomologous chromosomes.
What happens in a chromosomal insertion?
A segment from one chromosome is inserted into another chromosome.
Define chromosomal deletion and give an example.
Loss of a chromosome segment. Example: X-linked ichthyosis.
Define chromosomal duplication and give an example.
Repetition of a chromosome segment.
Example: Charcot-Marie-Tooth disease (CMT1A – duplication of 17p11.2).
What is chromosomal inversion and give an example?
A segment is reversed end to end.
Example: inv(9)(p11q12), common in 2% of the population.
What is nondisjunction?
Failure of chromosomes to separate properly during meiosis, resulting in aneuploidy.
What technique is used for rapid prenatal diagnosis of aneuploidy?
FISH (Fluorescence In Situ Hybridization).
What does Array CGH detect?
Gains or losses in DNA copy number across the genome.
What are clinical effects of Trisomy 21 (Down syndrome)?
Intellectual disability, characteristic facial features, congenital heart defects.
What are clinical effects of Trisomy 18 (Edward syndrome)?
Severe developmental delays, clenched fists, rocker-bottom feet, often fatal in infancy.
What are clinical effects of Trisomy 13 (Patau syndrome)?
Severe intellectual disability, cleft lip/palate, heart defects, microcephaly.
What are reproductive risks associated with balanced translocations?
~50% of conceptions may result in normal or balanced karyotype; others may lead to miscarriage or abnormal phenotype due to unbalanced products.
What chromosomal abnormality is associated with chronic myeloid leukemia (CML)?
Philadelphia chromosome – translocation t(9;22)(q34;q11.2) creating BCR-ABL fusion gene.
What does the BCR-ABL fusion gene do?
It produces a constitutively active tyrosine kinase that drives uncontrolled cell proliferation in CML.
