Ch 6 (pp 111-119)

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Questions and Answers

Which sex chromosome aneuploidy is associated with an extra copy of the SHOX gene, leading to elevated height?

47,XXY karyotype

47,XYY karyotype

XX male

47,XXX karyotype (correct)

Which gene triggers the process leading to male gonadal differentiation and is located just outside the pseudoautosomal region of the Y chromosome?

SOX9 gene

SHOX gene

SRY gene (correct)

XIST gene

What is the outcome of an offspring receiving an X chromosome with the SRY gene lying on it?

XXX female

XY female

XXY male

XX male (correct)

In which syndrome is the 47,XYY karyotype observed?

47,XYY Syndrome Signup and view all the answers

What is the approximate incidence of the 47,XXX karyotype?

1/1000 females Signup and view all the answers

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 Signup and view all the answers

What are the consequences of having four, five, or even more X chromosomes in females?

Increased intellectual disability and physical abnormality Signup and view all the answers

Which syndrome is caused by a deletion of the distal short arm of chromosome 5?

Cri-du-chat syndrome Signup and view all the answers

Which technique permits the detection of deletions that are often too small to be observed microscopically?

FISH and aCGH techniques Signup and view all the answers

What is the karyotype for Cri-du-chat syndrome?

46,XY,del(5p) Signup and view all the answers

Which syndrome is caused by a deletion of the distal short arm of chromosome 4?

Wolf-Hirschhorn syndrome Signup and view all the answers

What is the characteristic cry associated with Cri-du-chat syndrome?

Distinctive cry of the cat Signup and view all the answers

What is the average IQ of individuals with Cri-du-chat syndrome?

About 35 Signup and view all the answers

Which group of clinically significant chromosome abnormalities is the most common after the three autosomal aneuploidies described earlier?

Autosomal deletion syndromes Signup and view all the answers

What is the term for the cry associated with Cri-du-chat syndrome?

Cry of the cat Signup and view all the answers

What is the approximate occurrence rate of Cri-du-chat syndrome in live births?

1 in 50,000 Signup and view all the answers

What is the approximate frequency of trisomy 16 at conception?

15% Signup and view all the answers

What is the approximate frequency of aneuploidy in sperm cells?

3% Signup and view all the answers

What percentage of oocytes have missing or extra chromosomes?

25% Signup and view all the answers

What is the approximate frequency of XYY karyotype in the male prison population?

1/100 Signup and view all the answers

What percentage of conceptions have a chromosome abnormality?

10% to 20% Signup and view all the answers

What are the leading known cause of pregnancy loss?

Chromosome abnormalities Signup and view all the answers

What is the approximate incidence of structural abnormalities in oocytes?

5% Signup and view all the answers

Which type of translocation involves the fusion of the long arms of two nonhomologous chromosomes, specifically acrocentric chromosomes?

Robertsonian translocation Signup and view all the answers

What is the recurrence risk for parents of a child who has the nondisjunction type of Down syndrome?

1% Signup and view all the answers

What is responsible for approximately 5% of Down syndrome cases?

Robertsonian translocation Signup and view all the answers

What type of translocation occurs when breaks occur in two different chromosomes and the material is mutually exchanged?

Reciprocal translocation Signup and view all the answers

What can carriers of balanced reciprocal translocations produce in their offspring due to partial trisomy or monosomy?

Abnormal phenotypes Signup and view all the answers

What is the critical action to take whenever a condition like Down syndrome is suspected?

Order a chromosome study Signup and view all the answers

What type of deletions can occur as a result of a single break leading to the loss of the chromosome's tip?

Terminal deletions Signup and view all the answers

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.

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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.