30 Questions
Which sex chromosome aneuploidy is associated with an extra copy of the SHOX gene, leading to elevated height?
47,XXX karyotype
Which gene triggers the process leading to male gonadal differentiation and is located just outside the pseudoautosomal region of the Y chromosome?
SRY gene
What is the outcome of an offspring receiving an X chromosome with the SRY gene lying on it?
XX male
In which syndrome is the 47,XYY karyotype observed?
47,XYY Syndrome
What is the approximate incidence of the 47,XXX karyotype?
1/1000 females
What is the result of nondisjunction in the mother in approximately 90% of cases of the 47,XXX karyotype?
47,XXX karyotype in the offspring
What are the consequences of having four, five, or even more X chromosomes in females?
Increased intellectual disability and physical abnormality
Which syndrome is caused by a deletion of the distal short arm of chromosome 5?
Cri-du-chat syndrome
Which technique permits the detection of deletions that are often too small to be observed microscopically?
FISH and aCGH techniques
What is the karyotype for Cri-du-chat syndrome?
46,XY,del(5p)
Which syndrome is caused by a deletion of the distal short arm of chromosome 4?
Wolf-Hirschhorn syndrome
What is the characteristic cry associated with Cri-du-chat syndrome?
Distinctive cry of the cat
What is the average IQ of individuals with Cri-du-chat syndrome?
About 35
Which group of clinically significant chromosome abnormalities is the most common after the three autosomal aneuploidies described earlier?
Autosomal deletion syndromes
What is the term for the cry associated with Cri-du-chat syndrome?
Cry of the cat
What is the approximate occurrence rate of Cri-du-chat syndrome in live births?
1 in 50,000
What is the approximate frequency of trisomy 16 at conception?
15%
What is the approximate frequency of aneuploidy in sperm cells?
3%
What percentage of oocytes have missing or extra chromosomes?
25%
What is the approximate frequency of XYY karyotype in the male prison population?
1/100
What percentage of conceptions have a chromosome abnormality?
10% to 20%
What are the leading known cause of pregnancy loss?
Chromosome abnormalities
What is the approximate incidence of structural abnormalities in oocytes?
5%
Which type of translocation involves the fusion of the long arms of two nonhomologous chromosomes, specifically acrocentric chromosomes?
Robertsonian translocation
What is the recurrence risk for parents of a child who has the nondisjunction type of Down syndrome?
1%
What is responsible for approximately 5% of Down syndrome cases?
Robertsonian translocation
What type of translocation occurs when breaks occur in two different chromosomes and the material is mutually exchanged?
Reciprocal translocation
What can carriers of balanced reciprocal translocations produce in their offspring due to partial trisomy or monosomy?
Abnormal phenotypes
What is the critical action to take whenever a condition like Down syndrome is suspected?
Order a chromosome study
What type of deletions can occur as a result of a single break leading to the loss of the chromosome's tip?
Terminal deletions
Study Notes
Chromosomal Aberrations: Reciprocal and Robertsonian Translocations
- Balanced translocations are common in humans, occurring in 1 of every 500 to 1000 individuals.
- Reciprocal translocations occur when breaks occur in two different chromosomes and the material is mutually exchanged, potentially leading to offspring with duplications and deletions of genetic material.
- Robertsonian translocations involve the fusion of the long arms of two nonhomologous chromosomes, specifically acrocentric chromosomes (13, 14, 15, 21, and 22).
- Carriers of balanced reciprocal translocations usually have normal phenotypes, but their offspring might have abnormal phenotypes due to partial trisomy or monosomy.
- A common Robertsonian translocation involves fusion of the long arms of chromosomes 14 and 21, and is responsible for approximately 5% of Down syndrome cases.
- Fetuses with certain adjacent segregation patterns of Robertsonian translocations do not survive to term, and one pattern results in Down syndrome.
- The recurrence risk for parents of a child who has the nondisjunction type of Down syndrome is 1%, but for parents with a Robertsonian translocation, it's greater.
- The carrier of a Robertsonian translocation can produce conceptions with monosomy or trisomy of the long arms of acrocentric chromosomes.
- Deletions can occur as terminal deletions, caused by a single break leading to the loss of the chromosome's tip, or as interstitial deletions, resulting from two breaks and the loss of material between them.
- It is critical to order a chromosome study whenever a condition like Down syndrome is suspected, to identify the type of chromosomal aberration involved.
- Reciprocal translocations are caused by breaks on different chromosomes and a subsequent exchange of material, potentially leading to offspring with duplications and deletions of genetic material.
- Robertsonian translocations occur when the long arms of two acrocentric chromosomes fuse at the centromere, with potential implications for the carrier's offspring.
Test your knowledge of chromosomal aberrations with a quiz on reciprocal and Robertsonian translocations. Explore the genetic implications and inheritance patterns associated with these chromosomal rearrangements, and learn about their impact on conditions like Down syndrome.
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