Chromosomal Aberrations and Variations
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Questions and Answers

What is a consequence of deleting the centromere from a chromosome?

  • The chromosome undergoes interstitial deletion.
  • The chromosome duplicates itself.
  • The chromosome becomes acentric and is lost. (correct)
  • The chromosome remains intact and functional.

    • Which term describes the event where a gene's loss results from a break in the chromosome?

  • Duplication
  • Translocation
  • Inversion
  • Deletion (correct)

    • What generally causes duplications in chromosomes during meiosis?

  • Acentric breakage
  • Unequal crossing over (correct)
  • Gene mutation
  • Chromosomal translocation

    • What is the impact of a deletion in the wild-type allele of a heterozygote?

    <p>It may cause a mutant phenotype.</p> Signup and view all the answers

    How can a deletion be categorized based on its location on a chromosome?

    <p>Terminal or interstitial</p> Signup and view all the answers

    Which of the following is an example of a disorder caused by large chromosomal deletions?

    <p>Cri-du-chat syndrome</p> Signup and view all the answers

    What happens during misalignment of chromosomes during crossing over?

    <p>Unequal exchange products occur.</p> Signup and view all the answers

    Which of the following statements is true regarding duplications and deletions?

    <p>Deletions can result in severe consequences, while duplications typically do not.</p> Signup and view all the answers

    What is the primary consequence of crossing-over occurring in an inversion during meiosis in a heterozygote?

    <p>Unequal crossover resulting in genetic imbalances</p> Signup and view all the answers

    What defines a duplication loop during prophase I?

    <p>Pairing of chromosomes in duplication heterozygotes</p> Signup and view all the answers

    What happens to gametes produced from pericentric and paracentric inversions?

    <p>They are imbalanced</p> Signup and view all the answers

    Which type of translocation involves the reunion of broken segments to incorrect partners?

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

    Which process is characterized by a chromosome segment excising and reintegrating at a 180° orientation?

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

    How does a homozygote differ in meiotic consequences when compared to a heterozygote during inversion?

    <p>Inversions do not affect homozygotes</p> Signup and view all the answers

    Which type of duplication is exemplified by the Drosophila eye shape allele, Bar?

    <p>Simple duplication</p> Signup and view all the answers

    What is characterized as the transfer of a chromosome segment to a different part of the same chromosome or a different chromosome?

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

    What are the two primary ways in which the structure of chromosomes can be altered?

    <p>Change in total genetic information and rearrangement of existing genetic material</p> Signup and view all the answers

    Which term refers to substantial changes in chromosome structure affecting more than one gene?

    <p>Chromosomal aberrations</p> Signup and view all the answers

    Which structural alteration involves a segment of the chromosome being removed?

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

    What type of structural alteration maintains the same genetic material but rearranges its order?

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

    What may be a consequence of chromosomal aberrations?

    <p>Development of birth defects or mental retardation</p> Signup and view all the answers

    Which of the following statements is true regarding duplication in chromosome structure?

    <p>It creates an additional segment of a chromosome</p> Signup and view all the answers

    Which of the following describes translocation in chromosomal alterations?

    <p>A section of one chromosome is moved to a different chromosome</p> Signup and view all the answers

    Chromosomal aberrations can lead to which of the following outcomes?

    <p>Increased risks for infertility</p> Signup and view all the answers

    Chromosomal mutations can also be referred to as:

    <p>Chromosomal rearrangements</p> Signup and view all the answers

    What best describes the impact of chromosomal aberrations on genetic information?

    <p>They can either increase or decrease the total genetic content</p> Signup and view all the answers

    Study Notes

    Introduction

    • Chromosomes can undergo changes, known as structural variations or chromosomal aberrations.
    • These changes can affect the structure of the chromosome itself or the number of chromosomes.
    • Structural chromosomal rearrangements can cause birth defects, mental retardation, and infertility.
    • Allelic variations are due to mutations in specific genes.
    • Chromosomal aberrations are significant changes in chromosome structure, affecting multiple genes.
    • They are also known as chromosomal mutations.

    Alterations in Chromosome Structure

    • There are two main ways chromosome structure can change.
      • The total amount of genetic information in the chromosome can change.
      • The genetic material can remain the same but be rearranged.

    Duplication

    • Duplication involves the addition of one or more genes to a chromosome due to the attachment of a chromosomal fragment.
    • When there is a duplication in one chromosome, there is a corresponding deletion in the other chromosome.
    • Duplications often originate from unequal crossing over during meiosis.
    • If homologous chromosomes are misaligned during pairing, unequal exchange products can be formed.
    • Duplications generally do not have drastic consequences for phenotype or survival compared to deletions.
    • An example is the Drosophila eye shape allele, Bar, which reduces the number of eye facets, giving the eye a slit-like appearance.
    • Duplication loops form when chromosomes pair in duplication heterozygotes.
    • In prophase I, the duplication loop can take on different configurations that maximize the pairing of related regions.

    Deletions

    • A deficiency means deletion of a small part of a chromosome, resulting in the loss of one or more genes.
    • Deficiencies can originate from breakage occurring in both chromatids of a chromosome (chromosome break) or only in one chromatid (chromatid break).
    • The breakage can be caused by radiation, chemicals, drugs or viruses at any point in the cell cycle, in somatic or germ cells.
    • A deletion can be terminal when a single break occurs near the end of the chromosome or interstitial when two breaks occur in the middle.
    • The effect of a deletion depends on what genetic material is lost.
    • A deletion in one allele of a homozygous wild-type organism may have no impact on phenotype, while the same deletion in the wild-type allele of a heterozygote could lead to a mutant phenotype.
    • Deletion of the centromere results in an acentric chromosome, which is lost, often with serious or lethal consequences.
    • Examples of human disorders caused by large chromosomal deletions include:
      • Cri-du-chat (“cry of the cat”) syndrome, resulting from deletion of part of the short arm of chromosome 5.
      • This deletion leads to severe mental retardation and physical abnormalities.

    Inversion

    • Inversion occurs when a chromosome segment breaks and reintegrates in the opposite orientation.
    • There are two types:
      • Pericentric: Breakage occurs within the centromere, including the centromere.
      • Paracentric: Breakage occurs outside the centromere, does not include the centromere.
    • Linked genes are often inverted together.
    • The meiotic consequences depend on whether the inversion occurs in a homozygote or a heterozygote.
    • A homozygote will have normal meiosis.
    • In a heterozygote, the effect depends on whether crossing-over occurs.
      • If there is no crossing-over, no meiotic problems occur.
      • If crossing-over occurs within the inversion, unequal crossover can have serious genetic consequences.
    • An inversion loop forms in the heterozygote for the tightest possible alignment of homologous regions.
    • Gametes produced from pericentric and paracentric inversions are imbalanced.

    Translocation

    • The transfer of a chromosome segment to a different part of the same chromosome or to a different chromosome is known as translocation.
    • There are two main types:
      • Simple: A small terminal segment of a chromosome attaches to the end of a homologous or non-homologous chromosome.
      • Reciprocal: Breakage occurs in two non-homologous chromosomes, followed by the reunion of the broken segments to the wrong partners.

    History

    • The discovery of chromosomal aberrations dates back to:
      • 1926: A.H. Sturtevant discovered inversions in chromosomes.
      • 1923: C.B. Bridges discovered duplications, deletions and translocations in chromosomes.

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    Description

    This quiz explores the changes in chromosome structure, known as chromosomal aberrations. You'll learn about duplication, deletions, and their implications on genetic information. Understand how these variations can lead to various genetic disorders and their significance in genetics.

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