Chromosomal Abnormalities
| Fetal (about half of early losses) | Chromosomal abnormalities (50% of early miscarriages): trisomies (the commonest is trisomy 16), triploidy, monosomy X; structural defects; multiple pregnancy; degeneration of villi |
Chromosomal Abnormalities
- Nondisjunction is the failure of homologous chromosomes to separate during meiosis I, or sister chromatids to separate during meiosis II or mitosis. This is a major cause of aneuploidy (abnormal number of chromosomes).
- Common chromosomal syndromes include:
- Cri-du-chat syndrome: Caused by a partial deletion of the short arm of chromosome 5 (5p deletion). Characterized by a distinctive high-pitched cry resembling a cat's meow, intellectual disability, and microcephaly.
- Klinefelter's syndrome: Caused by nondisjunction of sex chromosomes, resulting in a 47,XXY karyotype. Individuals are typically male with tall stature, hypogonadism, infertility, and sometimes learning difficulties.
- Down syndrome (Trisomy 21): The most common chromosomal disorder, caused by the presence of an extra copy of chromosome 21. Most cases (approximately 95%) are due to meiotic nondisjunction, resulting in a karyotype of 47 chromosomes, trisom
Read this in Medical Biochemistry, Genetics, and Molecular Biology
What our notes say
- | Fetal (about half of early losses) | Chromosomal abnormalities (50% of early miscarriages): trisomies (the commonest is trisomy 16), triploidy, monosomy X; structural defects; multiple pregnancy; degeneration of villi | (Abortion and miscarriage)
- Cytogenetic (chromosomal) abnormalities are broadly divided into numerical and structural abnormalities, and may affect either autosomes or sex chromosomes. (Genetic Disorders CAT: Key Terms & Inheritance Patterns Explained)
- Cancer Diagnosis and Prognosis: Chromosomal abnormalities, such as translocations (e.g., Philadelphia chromosome in chronic myelogenous leukemia), are critical for diagnosing cancers and determining prognosis. (Molecular Biology,Molecular Genetics & Microbial-Biochemistry LAQs & SAQs)
- Prenatal Screening: Chromosomal analysis (e.g., amniocentesis or CVS) is used to detect chromosomal abnormalities in a fetus, such as trisomies or other congenital disorders. (Molecular Biology,Molecular Genetics & Microbial-Biochemistry LAQs & SAQs)
- Chromosomal abnormalities (the commonest cause, in about half of early losses): trisomies, monosomy X and triploidy. (Year 6 Gynaecology CAT 1 (MBOG 6511): 13 December 2019, 4 short answers and 16 M)
- Accumulation of additional genetic mutations and chromosomal abnormalities. (Female rep y3 — Past Paper Questions & Answers)
Study material on Chromosomal Abnormalities
- Molecular Biology,Molecular Genetics & Microbial-Biochemistry LAQs & SAQs
- Genetic Disorders MCQs Examination (Part 2)
- Weekly Year 2: Molecular Genetics and Cytogenetics Exam - July 17, 2026 (Section A: MCQs)
- INTRODUCTION TO GENETIC DISORDERS AND MUTATIONS MCQs
Practice questions on Chromosomal Abnormalities
What percentage of first-trimester spontaneous abortions are associated with chromosomal abnormalities?
- 25%
- 35%
- 50%
- 75%
- Occurs only after chronic exposure
Answer: C. Approximately 50% of first-trimester spontaneous abortions are associated with chromosomal abnormalities. ---
Approximately what percentage of first-trimester spontaneous abortions have chromosomal abnormalities?
- 10%
- 25%
- 50%
- 75%
- Reduced by routine feedback control
Answer: C. Approximately 50% of first-trimester spontaneous abortions have demonstrable chromosomal abnormalities, highlighting the importance of chromosomal integrity for fetal development. ---
Which statement about chromosomal abnormalities is correct?
- Loss of chromosomal material is better tolerated than gain
- Gain of chromosomal material produces more severe defects than loss
- Loss of chromosomal material produces more severe defects than gain
- Loss and gain produce identical effects
- Mostly unchanged in early disease
Answer: C. In general, loss of chromosomal material produces more severe defects than does gain of chromosomal material, which is why monosomies are typically more severe than trisomies. ---
Which THREE autosomal trisomies were among the first chromosomal abnormalities identified?
- 13, 18, and 21
- 8, 13, and 18
- 15, 18, and 21
- 13, 15, and 21
- Occurs only after chronic exposure
Answer: A. Trisomies 21, 18, and 13 were among the first chromosomal abnormalities identified, along with cri du chat syndrome (5p deletion). ---
Approximately what percentage of early pregnancy miscarriages have demonstrable chromosomal abnormalities?
- 25%
- 35%
- 50%
- 75%
- Occurs only after chronic exposure
Answer: C. Approximately 50% of early pregnancy miscarriages have demonstrable chromosomal abnormalities, highlighting the significant impact of genetic disorders on early development. ---
What is the clinical implication of 50% of early miscarriages having chromosomal abnormalities?
- Chromosomal abnormalities are rare
- Most chromosomal abnormalities are compatible with life
- Chromosomal abnormalities are major cause of pregnancy loss
- All miscarriages are genetic
- Mostly unchanged in early disease
Answer: C. The fact that approximately 50% of early pregnancy miscarriages have demonstrable chromosomal abnormalities indicates that chromosomal abnormalities are a major cause of early pregnancy loss and many are incompatible with continued development.