CSC Genetics Flashcards
(14 cards)
What are the main types of chromosomal abnormalities?
Two types: numerical (wrong number of chromosomes) and structural (chromosomes broken or rearranged).
Numerical: Polyploidy (extra chromosome sets, e.g., triploidy) and aneuploidy (extra/missing chromosomes, e.g., Trisomy 21). Structural: Deletions (e.g., Cri du Chat), duplications, inversions (paracentric/pericentric), translocations (reciprocal/Robertsonian), ring chromosomes, isochromosomes.
What are the key features of Trisomy 21, 18, and 13?
These are extra chromosome conditions causing syndromes with distinct issues.
Trisomy 21 (Down Syndrome): Extra chromosome 21; flat face, slanted eyes, heart defects, mental retardation; 1/800 births; maternal age risk. Trisomy 18 (Edwards Syndrome): Extra chromosome 18; microcephaly, heart defects, rocker bottom feet; 1/7500 births; rarely survive. Trisomy 13 (Patau Syndrome): Extra chromosome 13; polydactyly, cleft lip/palate, severe retardation; 1/20,000 births; most die early.
How do Prader-Willi and Angelman syndromes differ despite the same chromosome 15 deletion?
Same missing chromosome piece, but from dad (Prader-Willi: overeating, obesity) or mom (Angelman: seizures, laughter).
Both due to chromosome 15q deletion but differ by parental origin (genomic imprinting): Prader-Willi: Paternal deletion; hyperphagia, obesity, poor muscle tone, intellectual impairment. Angelman: Maternal deletion; seizures, severe intellectual impairment, absent speech, spontaneous laughter.
What is a Robertsonian translocation, and why is it significant?
Two chromosomes stick together, losing small bits, and can cause Down syndrome in kids, especially if mom carries it.
Fuses long arms of two acrocentric chromosomes (13, 14, 15, 21, 22), losing short arms, reducing chromosome count. Common: 13q14q (1/1300), 14q21q (linked to Down syndrome). Female carriers have higher risk of unbalanced offspring (e.g., Trisomy 21).
What is the most common viable chromosomal abnormality, and what is its usual cause?
Trisomy 21 (Down syndrome); caused by nondisjunction in meiosis I, especially in older maternal age.
What syndrome is associated with a 45,X karyotype and features such as short stature, webbed neck, and infertility?
Turner syndrome. Only viable monosomy. Females with a single X chromosome.
Which structural rearrangement involves fusion of two acrocentric chromosomes and may cause familial Down syndrome?
Robertsonian translocation, often between chromosomes 14 and 21.
What distinguishes nondisjunction in meiosis I from meiosis II?
• Meiosis I: Gamete receives one maternal + one paternal homolog
• Meiosis II: Gamete receives two maternal or two paternal copies
Which syndrome results from deletion of paternal chromosome 15, and what are its features?
Prader-Willi syndrome: hyperphagia, obesity, hypotonia, hypogonadism, moderate intellectual impairment.
Which sex chromosome syndrome is associated with karyotype 47,XXY and features like gynecomastia, infertility, and tall stature?
Klinefelter syndrome
What are the clinical features of Trisomy 18 (Edwards syndrome)?
Micrognathia, rocker-bottom feet, clenched fists, severe intellectual disability, congenital heart defects.
What genetic mechanism explains the difference between Prader-Willi and Angelman syndromes?
Genomic imprinting. Same region of chromosome 15 deleted, but parent of origin determines syndrome (paternal = Prader-Willi, maternal = Angelman).
What is an interstitial deletion and name one syndrome caused by it?
Deletion in the middle of a chromosome (requires two breaks).
Example: Angelman or Prader-Willi syndrome (chromosome 15).
What is a balanced translocation, and what is the clinical significance?
All genetic material is present but rearranged; usually asymptomatic in carrier but can cause unbalanced gametes in offspring → risk of miscarriage or syndromes.
