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Questions and Answers
Which of the following accurately describes Down Syndrome in relation to chromosomal abnormalities?
Which of the following accurately describes Down Syndrome in relation to chromosomal abnormalities?
What genetic condition is associated with the karyotype 47,XX,+21?
What genetic condition is associated with the karyotype 47,XX,+21?
Which of the following statements about aneuploidies is correct?
Which of the following statements about aneuploidies is correct?
Which statement accurately describes aneuploidy?
Which statement accurately describes aneuploidy?
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What is the primary difference between polyploidy and aneuploidy?
What is the primary difference between polyploidy and aneuploidy?
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Which mechanism is primarily responsible for nondisjunction during meiosis?
Which mechanism is primarily responsible for nondisjunction during meiosis?
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What type of chromosomal abnormality is defined as having three copies of every chromosome, resulting in 69 chromosomes?
What type of chromosomal abnormality is defined as having three copies of every chromosome, resulting in 69 chromosomes?
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Which of the following best defines the process of polypoidy?
Which of the following best defines the process of polypoidy?
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In what situation does nondisjunction occur in Meiosis I?
In what situation does nondisjunction occur in Meiosis I?
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Which of the following terms describes a structural chromosomal abnormality without any gain or loss of genetic material?
Which of the following terms describes a structural chromosomal abnormality without any gain or loss of genetic material?
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Which karyotype represents a male with Turner syndrome?
Which karyotype represents a male with Turner syndrome?
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Which structural abnormality involves a segment of a chromosome being reversed end to end?
Which structural abnormality involves a segment of a chromosome being reversed end to end?
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What condition is characterized by a female having 46 chromosomes, with a structural translocation between chromosomes 1 and 6?
What condition is characterized by a female having 46 chromosomes, with a structural translocation between chromosomes 1 and 6?
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Which type of chromosomal abnormality is characterized by a change in the internal structure without altering the total number of chromosomes?
Which type of chromosomal abnormality is characterized by a change in the internal structure without altering the total number of chromosomes?
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What is a common characteristic of unbalanced chromosome abnormalities?
What is a common characteristic of unbalanced chromosome abnormalities?
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Which of the following syndromes is most likely caused by a chromosomal deletion?
Which of the following syndromes is most likely caused by a chromosomal deletion?
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Which mechanism is primarily responsible for numerical abnormalities, such as Down Syndrome?
Which mechanism is primarily responsible for numerical abnormalities, such as Down Syndrome?
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Polyploidy can result from which of the following processes?
Polyploidy can result from which of the following processes?
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Providing an example of a chromosomal rearrangement that may cause a phenotype change, which of the following is a correct pairing?
Providing an example of a chromosomal rearrangement that may cause a phenotype change, which of the following is a correct pairing?
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Which type of syndrome is often less severe due to the nature of genetic change?
Which type of syndrome is often less severe due to the nature of genetic change?
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Which statement about individuals with balanced rearrangements is true?
Which statement about individuals with balanced rearrangements is true?
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What is the primary cause of most structural chromosomal abnormalities?
What is the primary cause of most structural chromosomal abnormalities?
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What defines a karyotype?
What defines a karyotype?
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Which of the following options describes unbalanced rearrangements?
Which of the following options describes unbalanced rearrangements?
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Which chromosomes are known to be acrocentric and can participate in Robertsonian translocations?
Which chromosomes are known to be acrocentric and can participate in Robertsonian translocations?
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What is the purpose of chromosomal band nomenclature?
What is the purpose of chromosomal band nomenclature?
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What is the primary characteristic of balanced chromosomal abnormalities?
What is the primary characteristic of balanced chromosomal abnormalities?
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Which of the following is an example of an unbalanced chromosomal abnormality?
Which of the following is an example of an unbalanced chromosomal abnormality?
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What is the expected phenotypic effect of individuals with balanced chromosomal rearrangements?
What is the expected phenotypic effect of individuals with balanced chromosomal rearrangements?
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Why are deletion syndromes often more severe than duplication syndromes?
Why are deletion syndromes often more severe than duplication syndromes?
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Which of the following statements accurately describes numerical abnormalities?
Which of the following statements accurately describes numerical abnormalities?
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What type of chromosomal rearrangement could lead to conditions like Hemophilia A?
What type of chromosomal rearrangement could lead to conditions like Hemophilia A?
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Which syndrome is likely caused by a chromosomal deletion?
Which syndrome is likely caused by a chromosomal deletion?
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What tends to be the result of many unbalanced chromosomal rearrangements?
What tends to be the result of many unbalanced chromosomal rearrangements?
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What does the notation 'del(22)(q21)' in a karyotype signify?
What does the notation 'del(22)(q21)' in a karyotype signify?
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What is the primary characteristic of a balanced rearrangement?
What is the primary characteristic of a balanced rearrangement?
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In the karyotype notation '46,XX,t(1;6)(p23;q21)', what does 't' indicate?
In the karyotype notation '46,XX,t(1;6)(p23;q21)', what does 't' indicate?
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Which karyotype represents a structural abnormality involving an inversion?
Which karyotype represents a structural abnormality involving an inversion?
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What chromosomal feature is described by the term 'iso' in 'i(7)'?
What chromosomal feature is described by the term 'iso' in 'i(7)'?
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What type of chromosomal abnormality does '47,XX,+21' represent?
What type of chromosomal abnormality does '47,XX,+21' represent?
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What does a karyotype of '45,X/46,XX' indicate?
What does a karyotype of '45,X/46,XX' indicate?
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In which structural abnormality is there a segment of the chromosome reversed end to end?
In which structural abnormality is there a segment of the chromosome reversed end to end?
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Describe Non-Disjunction (Meiosis I)
Describe Non-Disjunction (Meiosis I)
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If two chromosomes are not identical then non-disjunction occurred in.....?
If two chromosomes are not identical then non-disjunction occurred in.....?
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If chromosomes are identical in the offspring then non-disjunction occurred in.....
If chromosomes are identical in the offspring then non-disjunction occurred in.....
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Is it possible to determine where non disjunction occurred in monosomies or trisomies? (both examples of aneuploidy)
Is it possible to determine where non disjunction occurred in monosomies or trisomies? (both examples of aneuploidy)
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Non-disjunction in meiosis I leads to what chromosomal pattern in offspring?
Non-disjunction in meiosis I leads to what chromosomal pattern in offspring?
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Non-disjunction in Meiosis II leads to what chromosomal pattern in offspring?
Non-disjunction in Meiosis II leads to what chromosomal pattern in offspring?
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Non-disjunction most often occurs in _____
Non-disjunction most often occurs in _____
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polyploidy (such as triploidy and tetraploidy) is ........ compatible with life. (examples include 47 XXX, 47 XXY, 47 XYY)
polyploidy (such as triploidy and tetraploidy) is ........ compatible with life. (examples include 47 XXX, 47 XXY, 47 XYY)
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What are balanced abnormalities in cytogenetics?
What are balanced abnormalities in cytogenetics?
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What are unbalanced abnormalities?
What are unbalanced abnormalities?
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Syndromes caused by chromosomal deletions are __________ than those caused by duplications, suggesting that the loss of genetic material is more disruptive than a gain.
Syndromes caused by chromosomal deletions are __________ than those caused by duplications, suggesting that the loss of genetic material is more disruptive than a gain.
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Hemophilia A is an ______ that disrupts the ______ gene.
Hemophilia A is an ______ that disrupts the ______ gene.
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Female Duchenne Muscular Dystrophy is caused by a ______ mutation between the ______ and ______.
Female Duchenne Muscular Dystrophy is caused by a ______ mutation between the ______ and ______.
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What happens when unequal crossing over occurs in chromosome bivalents?
What happens when unequal crossing over occurs in chromosome bivalents?
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What are acrocentric chromosomes in humans?
What are acrocentric chromosomes in humans?
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Describe Karyotype
Describe Karyotype
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What does colchicine and hypotonic saline do in karyotyping?
What does colchicine and hypotonic saline do in karyotyping?
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what does 47, XY, +18 mean?
what does 47, XY, +18 mean?
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what is q and p?
what is q and p?
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What is Robertsonian Translocation?
What is Robertsonian Translocation?
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What are acrocentric chromosomes?
What are acrocentric chromosomes?
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Describe a robertsonian translocation
Describe a robertsonian translocation
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what are ribosomal RNA genes?
what are ribosomal RNA genes?
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Study Notes
Chromosome Abnormalities & Cytogenetics
-
Structural chromosome abnormalities change the structure of chromosomes, but not the total number.
-
Balanced abnormalities have no gain or loss of genetic material and typically have no phenotypic effect.
- Examples: inversions, translocations.
-
Unbalanced abnormalities result in a gain or loss of genetic material, almost always leading to phenotypic effects.
- Examples: deletions, duplications.
-
Balanced abnormalities have no gain or loss of genetic material and typically have no phenotypic effect.
Numerical Abnormalities
- Numerical abnormalities involve alterations in the normal number of chromosomes (46).
- Polyploidy is a change in the full set of chromosomes. For example, triploidy involves having three full copies, resulting in 69 chromosomes. Triploidy is incompatible with life.
- Aneuploidy is a change in the number of one or more chromosomes. Trisomy and monosomy, involving a single chromosome, are most common, but changes involving multiple chromosomes can also occur.
Causes of Aneuploidy
- Aneuploidy is caused by non-disjunction during parental meiosis.
- If in a trisomy, the two chromosomes from the same parent are identical, the non-disjunction occurred in Meiosis II.
- If they are different, the non-disjunction occurred in Meiosis I.
Structural Chromosome Abnormalities
- Unequal crossing over is the mechanism that causes most structural abnormalities. It involves misalignment of repeat sequences during a parental meiosis.
Nomenclature of Chromosome Bands
-
p
,q
,cen
,ter
describe chromosomal locations or features. -
del
,dup
,inv
,t
,/
,+
,-
describe structural abnormalities. -
ish
indicates in situ hybridization, a cytogenetic technique used to label specific genes or loci. -
i
signifies "iso" - two copies of the same chromosome arm attached to the centromere. - Normal karyotypes are represented as 46,XX or 46,XY.
Examples of Structural Abnormalities
-
46,XY,del(22)(q21)
: a male with 46 chromosomes and a deletion on chromosome 22 at band q21. -
46,XX,inv(7)(p11;q22)
: a female with 46 chromosomes and an inversion on chromosome 7 with breakpoints at bands p11 and q22. -
47,XX,+21
: a female with an extra copy of chromosome 21 (trisomy 21 or Down syndrome). -
46,XX,t(1;6)(p23;q21)
: a female with 46 chromosomes and a translocation between chromosomes 1 and 6 with breakpoints at band p23 on chromosome 1 and band q21 on chromosome 6. -
45,X/46,XX
: a mosaic female with some 45,X cells (Turner Syndrome) and some 46,XX cells.
Summary of Chromosome Abnormalities
- Numerical abnormalities involve alterations in the normal number of chromosomes.
- Structural abnormalities do not change the total number of chromosomes but alter their internal structure.
- Balanced rearrangements have no gain or loss of genetic material and usually have no phenotypic effect.
- Unbalanced rearrangements involve a gain or loss of genetic material and almost always have phenotypic effects.
A Karyotype
- A karyotype is an individual’s complement of chromosomes and a display of these chromosomes.
- Chromosomes 13, 14, 15, 21, and 22 are acrocentric and can take part in Robertsonian translocations.
- Chromosomal band nomenclature is a standard method used to describe chromosomal locations and can help identify locations of abnormalities.
- Karyotype nomenclature is a standard way to describe normal karyotypes and numerical and structural chromosome abnormalities.
Learning Objectives
- Contrast numerical and structural chromosomal abnormalities.
- Define polyploidy and aneuploidy and explain their effects on human viability.
- Determine the parental meiosis during which a non-disjunction causing a trisomy occurred.
- Describe the major types of structural chromosomal rearrangements.
- Determine if a chromosomal rearrangement is balanced or unbalanced and predict its phenotypic effect.
- Describe a karyotype and identify gross abnormalities on a karyotype display.
- Interpret chromosomal band nomenclature and karyotype nomenclature to recognize chromosomal abnormalities and use these to predict the resulting clinical condition.
Chromosome Abnormalities and Cytogenetics: An Overview
- Structural chromosome abnormalities alter the internal structure of chromosomes, without changing the total number.
- Balanced abnormalities involve rearrangements without loss or gain of genetic material. These are typically phenotypically normal, except when breakpoints occur within crucial genes. Examples include inversions and translocations.
- Unbalanced abnormalities involve changes in genetic material (gain or loss). These often result in phenotypic effects. Examples include deletions and duplications.
- Numerical abnormalities always involve an imbalance in chromosome number and are therefore unbalanced.
- Individuals with balanced rearrangements are usually phenotypically normal, however, exceptions exist. For example, Hemophilia A can be caused by an inversion disrupting the F8 gene, and female Duchenne Muscular Dystrophy can be caused by a translocation between the X chromosome and an autosome.
- Deletion Syndromes: Deletions are usually more severe than duplications, as losing genetic material can disrupt essential functions. Common examples include Williams Syndrome, DiGeorge Syndrome, Angelman Syndrome, and Prader-Willi Syndrome.
- Duplication Syndromes: These are less common than deletion syndromes. One example is the WBSCR syndrome.
Karyotype Nomenclature
- Descriptive terms: terms like "p" (short arm), "q" (long arm), "cen" (centromere), and "ter" (telomere) are used to describe chromosome locations and features.
- Structural abnormality notations: Symbols like "del" (deletion), "dup" (duplication), "inv" (inversion), "t" (translocation), "/", "+", and "-" indicate structural changes.
- In Situ Hybridization (ISH): This technique is used to label specific genes or loci on chromosomes.
- **"i" or "iso":**Indicates two copies of the same chromosome arm attached to the centromere.
- Normal karyotypes: 46,XX (female) or 46,XY (male).
Examples of Structural Abnormalities
- 46,XY,del(22)(q21): A male with 46 chromosomes and a deletion on chromosome 22 at band q21.
- 46,XX,inv(7)(p11;q22): A female with 46 chromosomes and an inversion on chromosome 7 with breakpoints at bands p11 and q22.
- 47,XX,+21: A female with an extra copy of chromosome 21, known as trisomy 21 or Down Syndrome.
- 46,XX,t(1;6)(p23;q21): A female with 46 chromosomes and a translocation between chromosomes 1 and 6, with breakpoints at band p23 on chromosome 1 and q21 on chromosome 6.
- 45,X/46,XX: A mosaic female with some 45,X cells (Turner Syndrome) and some 46,XX cells.
Summary of Chromosome Abnormalities
- Numerical abnormalities affect the total chromosome number (46).
- Polyploidy involves changes in complete sets of chromosomes, e.g., triploidy (three full copies, 69 chromosomes), which is incompatible with life.
- Aneuploidy involves unequal changes in the number of individual chromosomes. Trisomy (extra chromosome) and monosomy (missing chromosome) are the most common, but changes in multiple chromosomes can also occur.
- Aneuploidy is caused by non-disjunction events during parental meiosis.
- Trisomy: if the two identical chromosomes come from the same parent, the non-disjunction occurred during Meiosis II. If they are different, it occurred during Meiosis I.
- Structural abnormalities alter the internal structure of chromosomes without changing the overall number.
- Balanced rearrangements have no gain or loss of genetic material and are usually phenotypically normal, although exceptions can occur. Examples include inversions and translocations.
- Unbalanced rearrangements involve a gain or loss of genetic material and almost always result in phenotypic effects. Examples are deletions and duplications.
- Unequal crossing over during parental meiosis is the primary mechanism for most structural abnormalities. It involves misalignment of repetitive sequences.
Further Summary
- A karyotype displays an individual's chromosome complement.
- Chromosomes 13, 14, 15, 21, and 22 are acrocentric and can participate in Robertsonian translocations.
- Chromosomal band nomenclature describes specific chromosomal locations.
- Karyotype nomenclature describes normal karyotypes and numerical and structural chromosomal abnormalities.
Learning Objectives
- Differentiate between numerical and structural chromosomal abnormalities and explain the mutational mechanisms involved.
- Define polyploidy and aneuploidy, summarizing their effects on human viability.
- Determine the parental meiotic stage where non-disjunction occurred to cause trisomy.
- Describe the types of structural rearrangements.
- Identify if a rearrangement is balanced or unbalanced and predict its phenotypic effect.
- Interpret and identify gross abnormalities in karyotypes.
- Understand chromosomal band and karyotype nomenclature to recognize abnormalities and predict clinical outcomes.
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Description
Test your knowledge on chromosome abnormalities, including both structural and numerical changes. This quiz covers concepts such as balanced and unbalanced abnormalities, polyploidy, and aneuploidy. Challenge yourself to understand the implications of these genetic variations.