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Questions and Answers
What characterizes paracentric inversions?
What characterizes paracentric inversions?
Which type of chromosomal alteration involves a change to a specific part of a chromosome?
Which type of chromosomal alteration involves a change to a specific part of a chromosome?
Which statement about chromosome inversions is true?
Which statement about chromosome inversions is true?
What is the frequency of paracentric inversions in the general population?
What is the frequency of paracentric inversions in the general population?
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What are the potential effects of structural chromosomal aberrations on an organism?
What are the potential effects of structural chromosomal aberrations on an organism?
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What is a potential reproductive issue for carriers of balanced Robertsonian translocations?
What is a potential reproductive issue for carriers of balanced Robertsonian translocations?
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What type of deletion occurs towards the end of a chromosome?
What type of deletion occurs towards the end of a chromosome?
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Which of the following is a symptom of Wolf-Hirschhorn syndrome?
Which of the following is a symptom of Wolf-Hirschhorn syndrome?
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What usually results from a deletion in homozygous individuals?
What usually results from a deletion in homozygous individuals?
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Which genes are deleted in individuals with Wolf-Hirschhorn syndrome?
Which genes are deleted in individuals with Wolf-Hirschhorn syndrome?
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What type of inversion can lead to recurrent pregnancy losses?
What type of inversion can lead to recurrent pregnancy losses?
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What is a possible outcome of intercalary deletion?
What is a possible outcome of intercalary deletion?
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What is the primary reason for the prevalence of pregnancy loss among couples with unbalanced chromosome rearrangements?
What is the primary reason for the prevalence of pregnancy loss among couples with unbalanced chromosome rearrangements?
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What is the primary cause of Williams Syndrome?
What is the primary cause of Williams Syndrome?
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Which statement about genomic imprinting is true?
Which statement about genomic imprinting is true?
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What characterizes reciprocal translocation?
What characterizes reciprocal translocation?
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Which of the following is a symptom of Williams Syndrome?
Which of the following is a symptom of Williams Syndrome?
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What happens in the case of the Philadelphia chromosome?
What happens in the case of the Philadelphia chromosome?
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Which of the following describes a primary consequence of the UBE3A gene imprinting?
Which of the following describes a primary consequence of the UBE3A gene imprinting?
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What differentiates Robertsonian translocation from reciprocal translocation?
What differentiates Robertsonian translocation from reciprocal translocation?
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What type of genetic material exchange occurs in translocation?
What type of genetic material exchange occurs in translocation?
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What happens when the SH3 domain of the protein is deleted?
What happens when the SH3 domain of the protein is deleted?
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What characterizes a Robertsonian translocation?
What characterizes a Robertsonian translocation?
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Which of the following conditions can result from genetically balanced carriers of Robertsonian translocations?
Which of the following conditions can result from genetically balanced carriers of Robertsonian translocations?
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In patients with a Robertsonian translocation involving chromosome 21, how many total chromosomes are present?
In patients with a Robertsonian translocation involving chromosome 21, how many total chromosomes are present?
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What is the cause of Charcot-Marie-Tooth disease type 1A?
What is the cause of Charcot-Marie-Tooth disease type 1A?
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Which of the following is NOT a type of duplication?
Which of the following is NOT a type of duplication?
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What is a significant characteristic of patients with a Robertsonian translocation associated with Down syndrome?
What is a significant characteristic of patients with a Robertsonian translocation associated with Down syndrome?
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Which chromosomes are generally involved in Robertsonian translocations?
Which chromosomes are generally involved in Robertsonian translocations?
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What is a common symptom of Cri-du-chat syndrome?
What is a common symptom of Cri-du-chat syndrome?
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Which gene's deletion is most strongly associated with severe intellectual disability in Cri-du-chat syndrome?
Which gene's deletion is most strongly associated with severe intellectual disability in Cri-du-chat syndrome?
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What phenotype is characteristic of Angelman syndrome?
What phenotype is characteristic of Angelman syndrome?
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What type of chromosomal deletion results in both Prader-Willi syndrome and Angelman syndrome?
What type of chromosomal deletion results in both Prader-Willi syndrome and Angelman syndrome?
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What is the role of the CTNND2 protein in the nervous system?
What is the role of the CTNND2 protein in the nervous system?
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Which of these symptoms is NOT associated with Prader-Willi syndrome?
Which of these symptoms is NOT associated with Prader-Willi syndrome?
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Which gene is responsible for the characteristics seen in Angelman syndrome?
Which gene is responsible for the characteristics seen in Angelman syndrome?
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What is the genetic cause of Cri-du-chat syndrome?
What is the genetic cause of Cri-du-chat syndrome?
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Study Notes
Chromosomal Aberrations
- Chromosomal aberrations are alterations in genetic information (chromosomes) that can negatively affect an organism.
- These alterations can be changes in chromosome number (covered in another section) or changes in chromosome structure.
Background
- Numerical aberrations (aneuploidy): Changes in the number of chromosomes.
- Structural aberrations: Changes in the specific chromosome parts.
- Polyploidy (3n): having 3 sets of chromosomes.
- Aneuploidy(2n ± 1): having one more or one less chromosomes.
Structural Aberrations
- Deletion: A part of the chromosome is lost. This mutation is irreversible, and human disorders are often caused by deletions in a single copy of a chromosome.
- Inversion: A section of a chromosome is reversed. Two breakpoints occur within the same chromosome; the section of the chromosome is inverted before being reinserted. Based on whether the inverted fragment includes the centromere, inversions can be classified as either pericentric or paracentric.
- Duplication: Extra copies of a chromosome segment are present. The segment could be repeated in tandem, or not in tandem.
- Translocation: Genetic material swaps between non-homologous chromosomes. There are two main types, reciprocal (an exchange between non-homologous chromosomes) and Robertsonian (a fusion of two acrocentric chromosomes).
Inversion
- Chromosome inversions are defined as a chromosome rearrangement produced by two breakpoints in the same chromosome. The resulting fragment is inverted, and re-inserted in the chromosome.
- Paracentric inversions: Do not contain the centromere.
- Pericentric inversions: Contain the centromere.
- Frequency of paracentric inversion in the general population 1 in 10,000 to 5 in 10,000
- Frequency of pericentric inversion in the general population 1 in 10,000 to 7 in 10,000
Inversion and Reproduction Issues
- Carriers of balanced chromosome inversions usually have no direct health impact.
- However, unbalanced pericentric inversions create recombinants with deletions and duplications in the inverted segment.
- Unbalanced paracentric inversions create inverted duplications of segments.
- These imbalances can lead to reproduction issues like sterility/infertility or recurrent pregnancy loss (3-9% of couples with recurrent loss).
Deletion
- A chromosome segment is lost in a deletion. The lost fragment is usually degraded, making this change irreversible.
- Larger deletions typically lead to human disorders, whereas homozygotes are often lethal.
- Terminal deletion: Occurs towards the end of a chromosome.
- Intercalary deletion: Occurs from the middle (or interior) of a chromosome.
- Examples include Wolf-Hirschhorn syndrome and Cri-du-chat syndrome
Deletion (Specific Examples)
- Wolf-Hirschhorn syndrome: Deletion near the end of the short arm of chromosome 4. The missing genes include NSD2, LETM1, MSX1. Symptoms involve a characteristic facial appearance, developmental delays, and severe health problems.
- Cri-du-chat syndrome: Deletion in the beginning of the short arm (p) of chromosome 5. The loss of the CTNND2 gene is associated with intellectual disability. Some signs of the syndrome include a high-pitched crying sound ("cat cry"), low birth weight, small size, and a particular facial structure.
Deletion (Other Examples)
- Prader-Willi Syndrome & Angelman Syndrome : Both are caused by an intercalary deletion in chromosome 15, but differing on which parent carried the deleted segment.
- William's Syndrome: Caused by a microdeletion at 7q11.23. It is characterized by mild intellectual disability / learning difficulties, unique personality characteristics, distinct facial features and cardiovascular issues.
Duplication
- Duplication: Repetition of a chromosome segment. This repetition can be in tandem or non-tandem.
- Example of a duplication induced disease : Charcot-Marie-Tooth disease type 1A
- Charcot-Marie-Tooth disease type 1A: An inherited disorder affecting peripheral nerves. CMT1A is linked with the duplication of the PMP22 gene.
Translocation
- A translocation is the shuffling of genetic material along chromosomes. It involves two non-homologous chromosomes.
- Types include reciprocal translocation, an exchange between nonhomologous chromosomes and Robertsonian, a fusion of two acrocentric chromosomes.
- Philadelphia chromosome: A reciprocal translocation between chromosomes 9 and 22, leading to acute lymphoblastic leukemia and chronic myelogenous leukemia. The BCR-ABL gene is formed.
- Robertsonian Translocation (RobT): Typically acrocentric chromosomes (13, 14, 15, 21, 22). The resulting chromosome has shortened arms due to fusion of the long arms, and the short arms are lost. Increased risk of infertility and genetic problems in offspring, including risk for Down syndrome. The risk for Down syndrome (trisomy 21 ) and Patau syndrome (trisomy 13.) is higher in offspring of those carrying translocations.
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Description
Test your understanding of chromosomal alterations, specifically focusing on paracentric inversions and their implications. This quiz covers various aspects of chromosomal structure, syndromes like Wolf-Hirschhorn syndrome, and the consequences of deletions and inversions in genetics.
