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Chromosome Abnormalities & Cytogenetics
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Chromosome Abnormalities & Cytogenetics

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Questions and Answers

Which of the following accurately describes Down Syndrome in relation to chromosomal abnormalities?

  • It is caused by structural chromosomal rearrangements.
  • It is characterized by an extra copy of chromosome 21 due to nondisjunction. (correct)
  • It results from an unbalanced rearrangement involving chromosomes 13 and 15.
  • It is primarily a result of a Robertsonian translocation.

    • What genetic condition is associated with the karyotype 47,XX,+21?

  • Klinefelter syndrome
  • Down syndrome (correct)
  • Patau syndrome
  • Turner syndrome

    • Which of the following statements about aneuploidies is correct?

  • Aneuploidy generally arises from nondisjunction during meiosis. (correct)
  • Aneuploid conditions always lead to phenotypically visible traits.
  • Aneuploidy refers to variations in the number of whole sets of chromosomes.
  • Aneuploidy increases overall organism viability.

    • Which statement accurately describes aneuploidy?

    <p>It results from nondisjunction during cell division.</p> Signup and view all the answers

    What is the primary difference between polyploidy and aneuploidy?

    <p>Polyploidy involves additional chromosomes sets, while aneuploidy involves individual chromosome gain or loss.</p> Signup and view all the answers

    Which mechanism is primarily responsible for nondisjunction during meiosis?

    <p>The failure of homologous chromosomes or sister chromatids to separate.</p> Signup and view all the answers

    What type of chromosomal abnormality is defined as having three copies of every chromosome, resulting in 69 chromosomes?

    <p>Triploidy</p> Signup and view all the answers

    Which of the following best defines the process of polypoidy?

    <p>The duplication of every chromosome in a diploid organism.</p> Signup and view all the answers

    In what situation does nondisjunction occur in Meiosis I?

    <p>When both chromosomes from one parent are different.</p> Signup and view all the answers

    Which of the following terms describes a structural chromosomal abnormality without any gain or loss of genetic material?

    <p>Balanced rearrangement</p> Signup and view all the answers

    Which karyotype represents a male with Turner syndrome?

    <p>45,X/46,XX</p> Signup and view all the answers

    Which structural abnormality involves a segment of a chromosome being reversed end to end?

    <p>Inversion</p> Signup and view all the answers

    What condition is characterized by a female having 46 chromosomes, with a structural translocation between chromosomes 1 and 6?

    <p>Balanced translocation</p> Signup and view all the answers

    Which type of chromosomal abnormality is characterized by a change in the internal structure without altering the total number of chromosomes?

    <p>Structural balanced abnormalities</p> Signup and view all the answers

    What is a common characteristic of unbalanced chromosome abnormalities?

    <p>They result in phenotypic changes.</p> Signup and view all the answers

    Which of the following syndromes is most likely caused by a chromosomal deletion?

    <p>Prader Willi Syndrome</p> Signup and view all the answers

    Which mechanism is primarily responsible for numerical abnormalities, such as Down Syndrome?

    <p>Nondisjunction</p> Signup and view all the answers

    Polyploidy can result from which of the following processes?

    <p>Incomplete separation during meiosis</p> Signup and view all the answers

    Providing an example of a chromosomal rearrangement that may cause a phenotype change, which of the following is a correct pairing?

    <p>Translocation leading to Duchenne Muscular Dystrophy</p> Signup and view all the answers

    Which type of syndrome is often less severe due to the nature of genetic change?

    <p>Duplication syndromes</p> Signup and view all the answers

    Which statement about individuals with balanced rearrangements is true?

    <p>They usually have a normal phenotype.</p> Signup and view all the answers

    What is the primary cause of most structural chromosomal abnormalities?

    <p>Unequal crossing over</p> Signup and view all the answers

    What defines a karyotype?

    <p>An individual's complete set of chromosomes displayed visually</p> Signup and view all the answers

    Which of the following options describes unbalanced rearrangements?

    <p>Deletions and duplications of genetic material</p> Signup and view all the answers

    Which chromosomes are known to be acrocentric and can participate in Robertsonian translocations?

    <p>Chromosomes 13, 14, 15, 21, and 22</p> Signup and view all the answers

    What is the purpose of chromosomal band nomenclature?

    <p>To describe chromosomal locations of abnormalities</p> Signup and view all the answers

    What is the primary characteristic of balanced chromosomal abnormalities?

    <p>They involve a rearrangement without gains or losses of genetic material.</p> Signup and view all the answers

    Which of the following is an example of an unbalanced chromosomal abnormality?

    <p>Deletion</p> Signup and view all the answers

    What is the expected phenotypic effect of individuals with balanced chromosomal rearrangements?

    <p>They are typically phenotypically normal.</p> Signup and view all the answers

    Why are deletion syndromes often more severe than duplication syndromes?

    <p>Deletion syndromes result in more critical gene disruptions.</p> Signup and view all the answers

    Which of the following statements accurately describes numerical abnormalities?

    <p>They are always unbalanced.</p> Signup and view all the answers

    What type of chromosomal rearrangement could lead to conditions like Hemophilia A?

    <p>Inversion</p> Signup and view all the answers

    Which syndrome is likely caused by a chromosomal deletion?

    <p>Prader Willi Syndrome</p> Signup and view all the answers

    What tends to be the result of many unbalanced chromosomal rearrangements?

    <p>They almost always have phenotypic effects.</p> Signup and view all the answers

    What does the notation 'del(22)(q21)' in a karyotype signify?

    <p>A deletion on chromosome 22 at band q21</p> Signup and view all the answers

    What is the primary characteristic of a balanced rearrangement?

    <p>It typically has no phenotypic effect.</p> Signup and view all the answers

    In the karyotype notation '46,XX,t(1;6)(p23;q21)', what does 't' indicate?

    <p>A translocation between two chromosomes</p> Signup and view all the answers

    Which karyotype represents a structural abnormality involving an inversion?

    <p>46,XX,inv(7)(p11;q22)</p> Signup and view all the answers

    What chromosomal feature is described by the term 'iso' in 'i(7)'?

    <p>Two copies of the same chromosome arm attached to the centromere</p> Signup and view all the answers

    What type of chromosomal abnormality does '47,XX,+21' represent?

    <p>Trisomy for chromosome 21</p> Signup and view all the answers

    What does a karyotype of '45,X/46,XX' indicate?

    <p>A mosaic female with Turner syndrome</p> Signup and view all the answers

    In which structural abnormality is there a segment of the chromosome reversed end to end?

    <p>Inversion</p> Signup and view all the answers

    Describe Non-Disjunction (Meiosis I)

    <p>What Happens: In meiosis I, homologous chromosomes are supposed to separate into two different cells. If nondisjunction occurs, these chromosomes don't separate properly.</p> <p>Resulting Gametes:</p> <p>Two gametes will end up with an extra chromosome (n+1). Two gametes will end up missing a chromosome (n-1). Offspring Outcome:</p> <p>If an n+1 gamete (with an extra chromosome) fuses with a normal gamete (n), the offspring will have three copies of that chromosome (trisomy). If an n-1 gamete (missing a chromosome) fuses with a normal gamete (n), the offspring will have only one copy of that chromosome (monosomy).</p> Signup and view all the answers

    If two chromosomes are not identical then non-disjunction occurred in.....?

    <p>Meiosis I</p> Signup and view all the answers

    If chromosomes are identical in the offspring then non-disjunction occurred in.....

    <p>Meiosis II</p> Signup and view all the answers

    Is it possible to determine where non disjunction occurred in monosomies or trisomies? (both examples of aneuploidy)

    <p>Only trisomies you can determine where non-disjunction occurred (either mom side or dad side)</p> Signup and view all the answers

    Non-disjunction in meiosis I leads to what chromosomal pattern in offspring?

    <p>2 with trisomy, 2 with monosomy</p> Signup and view all the answers

    Non-disjunction in Meiosis II leads to what chromosomal pattern in offspring?

    <p>2 with trisomy (n+1), 2 normal (n)</p> Signup and view all the answers

    Non-disjunction most often occurs in _____

    <p>maternal Meiosis I</p> Signup and view all the answers

    polyploidy (such as triploidy and tetraploidy) is ........ compatible with life. (examples include 47 XXX, 47 XXY, 47 XYY)

    <p>NOT</p> Signup and view all the answers

    What are balanced abnormalities in cytogenetics?

    <p>Inversions and translocations</p> Signup and view all the answers

    What are unbalanced abnormalities?

    <p>Deletions and Duplications</p> Signup and view all the answers

    Syndromes caused by chromosomal deletions are __________ than those caused by duplications, suggesting that the loss of genetic material is more disruptive than a gain.

    <p>more severe</p> Signup and view all the answers

    Hemophilia A is an ______ that disrupts the ______ gene.

    <p>Inversion Mutation, F8</p> Signup and view all the answers

    Female Duchenne Muscular Dystrophy is caused by a ______ mutation between the ______ and ______.

    <p>Translocation, autosome, X chromosome</p> Signup and view all the answers

    What happens when unequal crossing over occurs in chromosome bivalents?

    <p>both chromosome with a deletion and a chromosome with a duplication will be generated. For every deletion syndrome there will be a corresponding duplication syndrome.</p> Signup and view all the answers

    What are acrocentric chromosomes in humans?

    <p>Chromosomes 13, 14, 15, 21, 22</p> Signup and view all the answers

    Describe Karyotype

    <ul> <li>a karyotype is an individuals complement of chromosomes</li> <li>G - Banding is chromosomal proteins stained with GIemsa</li> <li>Light bands = less condensed euchromatin</li> <li>Dark bands = more condensed heterochromatin</li> </ul> Signup and view all the answers

    What does colchicine and hypotonic saline do in karyotyping?

    <p>they block separation of chromosomes in anaphase and cells get stuck in M-phase and keep genetic material in most condensed form, the second thing causes cell to burst and kill all other structures</p> Signup and view all the answers

    what does 47, XY, +18 mean?

    <p>male, extra chromosome on number 18 (3 copies) indicated Edwards Syndrome</p> Signup and view all the answers

    what is q and p?

    <p>q (long arm) and p (short arm)</p> Signup and view all the answers

    What is Robertsonian Translocation?

    <p>Robertsonian translocation is a specific type of chromosomal rearrangement that involves the fusion of two acrocentric chromosomes.</p> Signup and view all the answers

    What are acrocentric chromosomes?

    <p>Humans have 23 pairs of chromosomes, and some of these are acrocentric chromosomes. Acrocentric chromosomes have a very short arm (called the p arm) and a long arm (called the q arm).</p> Signup and view all the answers

    Describe a robertsonian translocation

    <p>In Robertsonian translocation, two acrocentric chromosomes join together at their centromeres, forming a single chromosome with two long arms and usually losing the short arms. The short arms are typically lost because they contain redundant genetic material, such as ribosomal RNA genes, which are present in multiple copies elsewhere in the genome.</p> Signup and view all the answers

    what are ribosomal RNA genes?

    <p>Ribosomal RNA genes are essential components of the genome that encode rRNA, a crucial part of the ribosome's structure and function. These genes are found in multiple copies to meet the high demand for rRNA in protein synthesis, highlighting their vital role in cellular biology.</p> Signup and view all the answers

    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.

    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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    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.

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