Chromosomal Aberrations Overview

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Questions and Answers

Which condition is most likely to result from X chromosome monosomy?

  • Down syndrome
  • Turner syndrome (correct)
  • Fragile X syndrome
  • Klinefelter syndrome

What is the karyotype for a male with Down syndrome?

  • 46, XY, +21
  • 47, XX, +21
  • 46, XY, +18
  • 47, XY, +21 (correct)

Which best describes mixoploidy?

  • Presence of genetically different cell lineages within one individual (correct)
  • Presence of extra chromosomes in diploid cells
  • The presence of a Y chromosome in a female
  • Absence of a single homologous chromosome

How does mosaic Down syndrome occur?

<p>By the failure of chromosome 21 chromatids to separate during mitosis (B)</p> Signup and view all the answers

Which type of structural aberration occurs when a segment of one chromosome is inserted into another chromosome?

<p>Insertion (B)</p> Signup and view all the answers

What condition can result from the fusion of two different zygotes from double fertilization?

<p>Dispermic chimeras (C)</p> Signup and view all the answers

What characterizes balanced rearrangements in structural aberrations?

<p>They are generally harmless to the carrier. (A)</p> Signup and view all the answers

Which feature is NOT typically associated with Turner syndrome?

<p>Increased intelligence (C)</p> Signup and view all the answers

What characterizes the karyotype of an individual with Klinefelter syndrome?

<p>47, XXY (D)</p> Signup and view all the answers

What is the primary outcome of a deletion that involves loss of more than 2% of the total haploid genome?

<p>Lethal outcome. (A)</p> Signup and view all the answers

Which statement correctly defines monosomy?

<p>Absence of a single chromosome (B)</p> Signup and view all the answers

What occurs during a reciprocal translocation?

<p>Genetic material is exchanged between two chromosomes. (A)</p> Signup and view all the answers

In which situation would a karyotyping method most likely be used?

<p>Identifying chromosomal abnormalities (D)</p> Signup and view all the answers

Which structural aberration is likely to produce serious clinical effects due to an incorrect amount of chromosome material?

<p>Unbalanced rearrangement (D)</p> Signup and view all the answers

Which condition is typically associated with a karyotype of 47, XX, +21?

<p>Down syndrome (C)</p> Signup and view all the answers

Which of the following describes a condition where there is an entire extra set of chromosomes?

<p>Polyploidy (C)</p> Signup and view all the answers

Which scenario is most likely to result in triploidy?

<p>Dispermy of an ovum by two sperm (A)</p> Signup and view all the answers

Which of the following is true about aneuploidy concerning sex chromosomes compared to autosomes?

<p>Aneuploidy involving sex chromosomes typically has milder phenotypes. (A)</p> Signup and view all the answers

What is a known cause of aneuploidy linked to maternal age?

<p>Non-disjunction (B)</p> Signup and view all the answers

Which karyotype would represent a typical condition of tetraploidy?

<p>92 chromosomes grouped as four sets per chromosome (D)</p> Signup and view all the answers

Which of the following abnormalities is most likely associated with loss of a single chromosome?

<p>Monosomy (A)</p> Signup and view all the answers

What is the primary consequence of anaphase lag during cell division?

<p>Failure of one chromosome or chromatid to be included in daughter nuclei (C)</p> Signup and view all the answers

In which condition do the resulting cells have an abnormal chromosome number due to the addition of an extra chromosome?

<p>Aneuploidy (D)</p> Signup and view all the answers

What commonly leads to a triploid condition in a zygote?

<p>Fertilization by the fusion of two sperm with an egg (D)</p> Signup and view all the answers

What is the characteristic feature of balanced karyotypes?

<p>Normal chromosome number with all segments present (C)</p> Signup and view all the answers

What is the primary purpose of staining chromosomes during karyotyping?

<p>To enhance visibility of chromosomes under a light microscope (A)</p> Signup and view all the answers

Which statement accurately describes the karyotype formula for a normal male?

<p>46,XY (B)</p> Signup and view all the answers

In G-banding, which regions of DNA appear more darkly stained?

<p>AT-rich heterochromatic regions (D)</p> Signup and view all the answers

What would be the karyotype formula representation of a trisomy involving chromosome 8 in a female?

<p>47,XX,+8 (A)</p> Signup and view all the answers

What type of specimen is commonly used for karyotyping in cancer diagnoses?

<p>Tumor biopsies (A)</p> Signup and view all the answers

Which technique is NOT typically used for banding during karyotyping?

<p>FISH analysis (A)</p> Signup and view all the answers

What is indicated by a karyotype formula that includes a ‘-’ sign?

<p>Loss of a chromosome (B)</p> Signup and view all the answers

Which chromosome banding technique is particularly useful for analyzing chromosomes under a light microscope?

<p>G-banding (B)</p> Signup and view all the answers

Which of the following statements is true regarding X-linked dominant inheritance?

<p>An affected female has a 50% chance of transmitting the trait to any offspring regardless of sex. (C)</p> Signup and view all the answers

In X-linked hypophosphatemia, which characteristic differentiates males from females?

<p>Males have a higher severity of skeletal changes than females. (D)</p> Signup and view all the answers

Which of the following accurately describes Y-linked inheritance?

<p>A affected male transmits Y-linked traits only to his sons. (C)</p> Signup and view all the answers

What is a common result of deletions in Y chromosome genes?

<p>Infertility due to azoospermia. (C)</p> Signup and view all the answers

Which statement about karyotyping is correct?

<p>Karyotyping can determine an individual's entire chromosome complement. (C)</p> Signup and view all the answers

Why do females often exhibit less severe symptoms in X-linked dominant disorders?

<p>They carry two X chromosomes, which offer a protective effect. (A)</p> Signup and view all the answers

Which of the following conditions does NOT exemplify Y-linked inheritance?

<p>Color blindness in males. (A)</p> Signup and view all the answers

What distinguishes an X-linked dominant disorder from an X-linked recessive disorder?

<p>Both males and females are affected in X-linked dominant, with female manifestations being more severe. (C)</p> Signup and view all the answers

In families with X-linked dominant disorders, which outcome is typical?

<p>There is a higher prevalence of affected females compared to males. (C)</p> Signup and view all the answers

How does X chromosome inactivation impact the expression of X-linked traits in females?

<p>It completely silences one X chromosome, leading to reduced expression of X-linked traits. (B)</p> Signup and view all the answers

What is the expected chromosomal composition in a triploid individual?

<p>69 chromosomes with three copies of each chromosome (D)</p> Signup and view all the answers

Which of the following best characterizes aneuploidy?

<p>An abnormal number of chromosomes due to the loss or gain of individual chromosomes (B)</p> Signup and view all the answers

What is a common outcome associated with tetraploidy?

<p>Early developmental failures leading to miscarriage (B)</p> Signup and view all the answers

Which statement regarding non-disjunction and its outcomes is accurate?

<p>It can result from errors during meiosis I or meiosis II. (D)</p> Signup and view all the answers

How is triploidy most commonly caused?

<p>Resulting from fertilization by an egg with two sperm (A)</p> Signup and view all the answers

What is a characteristic feature of X-linked recessive inheritance?

<p>Males cannot transmit X-linked traits to their daughters. (A)</p> Signup and view all the answers

In a family where the father is affected by an X-linked recessive disorder, what is the probability that his daughter will be a carrier?

<p>50% chance of being a carrier. (D)</p> Signup and view all the answers

What is the recurrence risk for sons of a carrier female for an X-linked recessive disorder?

<p>50% chance of being affected. (C)</p> Signup and view all the answers

Which of the following statements is true regarding X-linked disorders like Duchenne muscular dystrophy?

<p>Affected males often die before reaching reproductive age. (C)</p> Signup and view all the answers

How do affected males typically contribute to the transmission of X-linked recessive disorders?

<p>They contribute through their healthy female carriers. (B)</p> Signup and view all the answers

What is a characteristic of autosomal dominant (AD) inheritance concerning affected individuals?

<p>Each affected person has an affected parent. (A)</p> Signup and view all the answers

Which of the following is true regarding the transmission of autosomal dominant traits?

<p>Vertical transmission is commonly observed. (D)</p> Signup and view all the answers

What role does a pedigree serve in genetic studies?

<p>It traces the inheritance pattern of traits within a family. (B)</p> Signup and view all the answers

How are autosomal dominant traits typically manifested in individuals?

<p>In the heterozygous state, often showing a milder phenotype. (D)</p> Signup and view all the answers

What is a common characteristic of traits that follow non-Mendelian inheritance patterns?

<p>They can be influenced by multiple genes or environmental factors. (A)</p> Signup and view all the answers

What is the primary difference between mosaic Down syndrome and standard Down syndrome?

<p>Mosaic Down syndrome contains cells with varying chromosome counts, while standard has uniform counts. (B)</p> Signup and view all the answers

Which of the following best describes how chimeric embryos are formed?

<p>Through the fusion of two zygotes from different fertilizations. (C)</p> Signup and view all the answers

What does the karyotype (45, X) indicate about an individual?

<p>The individual is likely female and has Turner syndrome. (B)</p> Signup and view all the answers

Which scenario describes mixoploidy involving mosaicism?

<p>A zygote develops with cells having different chromosome configurations due to disjunction failure. (C)</p> Signup and view all the answers

What is a common characteristic of individuals with Turner syndrome?

<p>They display normal intelligence but may experience learning disabilities. (C)</p> Signup and view all the answers

Flashcards

Karyotyping

A technique to detect large-scale genetic changes in chromosomes.

Mitotic cells

Cells arrested at metaphase/prometaphase of cell cycle for karyotyping.

Chromosome banding

Techniques like G-banding to visually differentiate chromosome regions.

G-banding

A common chromosome banding technique using Giemsa stain.

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Karyotype formula

A standardized way to describe chromosome number and structure.

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Numerical aberration

Changes in the number of chromosomes (e.g., trisomy, monosomy).

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Structural aberration

Changes in the structure of chromosomes (e.g., translocation).

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ISCN

International Standard for Cytogenetic Nomenclature for describing chromosome variations

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Euploidy

The normal number of chromosomes for a species. In humans, this is 46 chromosomes in somatic cells, and 23 chromosomes in gametes.

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Polyploidy

A condition with a chromosome number that is a multiple of the haploid set. For example, triploidy (3n) or tetraploidy (4n).

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Triploidy

A condition where there are three copies of each chromosome (3n). Often caused by failure of reduction division in meiosis.

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Tetraploidy

A condition where there are four copies of each chromosome (4n). Usually caused by failure of the first zygotic division.

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Aneuploidy

An abnormal chromosome number due to an extra or missing chromosome, but not involving the whole chromosome set.

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Non-disjunction

Failure of homologous chromosomes to separate in meiosis I or sister chromatids in meiosis II or mitosis. This can lead to aneuploidy.

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Anaphase lag

Failure of a chromosome or chromatid to be incorporated into a daughter nucleus during cell division due to delayed movement.

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Balanced Karyotype

A karyotype where the total amount of genetic material remains normal, even though there is a structural rearrangement of chromosomes.

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Unbalanced Karyotype

A karyotype where there is a gain or loss of genetic material due to a structural rearrangement.

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Phenotype

The observable characteristics of an organism, which are a result of both genetic and environmental factors.

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Trisomy

Having three copies of a chromosome instead of two in a diploid cell (2n+1).

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Monosomy

Having only one copy of a chromosome instead of two in a diploid cell.

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Down Syndrome Karyotype

The karyotype for Down syndrome is (47, XY, +21) for males and (47, XX, +21) for females.

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Turner Syndrome Karyotype

The karyotype for Turner syndrome is (45, X).

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Mixoploidy

The presence of two or more genetically different cell lineages within one individual.

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Mosaicism

Mixoploidy arising from the same zygote resulting in different cell lineages.

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Chimerism

Mixoploidy resulting from fusion of two different twin zygotes.

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Mosaic Down Syndrome

Down syndrome caused by nondisjunction during mitotic division, resulting in a mix of cells with different chromosome numbers.

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Dispermic Chimeras

Individuals formed by the fusion of two zygotes fertilized by two different sperm.

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True Hermaphroditism

A condition in dispermic chimeras where an individual has both ovarian and testicular tissue.

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What are structural aberrations?

Changes in the structure of chromosomes, often caused by breakage and reunion in different configurations. This can happen during crossing over (homologous chromosomes) or abnormally between non-homologous chromosomes.

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Balanced rearrangement

A type of structural aberration where the chromosome complement is complete, meaning there's no loss or gain of genetic material. This is usually harmless, unless a critical gene is damaged during the rearrangement.

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Unbalanced rearrangement

A type of structural aberration where the chromosome complement has an incorrect amount of genetic material due to loss or gain. These are often serious and can have clinical effects.

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Deletion (del)

A structural aberration where a part of a chromosome is lost. Losing more than 2% of the haploid genome is usually lethal.

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Translocation

A structural aberration where genetic material moves from one chromosome to another. This can be reciprocal (segments are exchanged) or non-reciprocal (one chromosome loses material with the other gaining).

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X-Linked Dominant Inheritance

A pattern of inheritance where a single copy of a mutated gene on the X chromosome is enough to cause the disorder in both males and females. Females are often less severely affected due to X chromosome inactivation.

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How does an affected father pass an X-linked dominant trait?

An affected father will transmit the trait to all of his daughters, but none of his sons, as he only passes on his Y chromosome to his sons.

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How does an affected mother pass an X-linked dominant trait?

An affected mother has a 50% chance of passing the trait to both her sons and daughters, regardless of their sex.

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X-linked hypophosphatemia

A disorder that affects bone growth and mineral metabolism, caused by mutations in the PHEX gene on the X chromosome. It leads to vitamin D-resistant rickets, affecting both males and females.

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Y-Linked Inheritance

A pattern of inheritance where a gene on the Y chromosome is passed only from father to son, affecting only males.

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Genes involved in Y-linked Inheritance

Genes on the Y chromosome primarily control male sexual development and spermatogenesis.

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Infertility in Y-linked inheritance

A deletion or mutation in a Y-linked gene involved in spermatogenesis can lead to infertility in males, as it affects sperm production.

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Purpose of Karyotyping

Used to detect genetic abnormalities like extra or missing chromosomes (aneuploidy), deletions, duplications, or rearrangements in chromosomes.

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What is analyzed in Karyotyping?

Karyotyping examines the number, size, and structure of chromosomes, looking for any deviations from the normal karyotype.

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Turner Syndrome

A genetic condition in females caused by the absence of one X chromosome, resulting in a 45, X karyotype.

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Pedigree Analysis

A family tree diagram that illustrates the inheritance pattern of a specific trait over generations.

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Autosomal Dominant Inheritance

A trait or disorder where a single copy of the mutated gene is sufficient to cause the condition, affecting both males and females equally.

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Punnett Square

A diagram used to predict the probability of different genotypes and phenotypes in the offspring of a cross.

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Vertical Transmission (Inheritance)

The pattern of a trait appearing in successive generations, with affected individuals having at least one affected parent.

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New Mutation

A spontaneous change in a gene that can result in an inherited disorder in an individual without a family history of the condition.

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X-linked recessive inheritance

A pattern of inheritance where a mutated gene on the X chromosome causes a disorder primarily in males. Females can be carriers but may not show symptoms.

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Obligate carrier

A female who carries a mutated X-linked recessive gene but does not display the disorder. She can still pass the gene to her sons.

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Duchenne muscular dystrophy

A severe X-linked recessive disorder affecting muscle development, leading to progressive weakness and often early death.

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Punnett square for X-linked recessive

A tool used to predict the probability of offspring inheriting an X-linked recessive disorder. Shows the possible combinations of X and Y chromosomes.

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Diagonal pattern of inheritance

The characteristic transmission of an X-linked recessive disorder through females, where affected males have affected maternal relatives.

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Study Notes

Chromosomal Aberrations (Numerical & Structural)

  • Interpreting chromosomal abnormalities is a key skill.
  • Aneuploidy vs. polyploidy differentiation is important. Aneuploidy involves an abnormal number of chromosomes (not a multiple of the haploid number), while polyploidy involves a multiple of the haploid number.
  • Balanced vs. unbalanced karyotypes are distinguished by the presence or absence of genetic material.
  • Phenotypic outcomes relate to the type of chromosomal aberration.

Numerical Aberrations

  • Euploidy refers to the normal chromosome number for a species. In humans, this is 46 (2n) in somatic cells and 23 (n) in gametes.
  • Polyploidy is a condition where the chromosome number is a multiple of the haploid set.
    • Triploidy (3n): A cell has three copies of each chromosome, often resulting from fertilization by two sperm or failure of reduction division in meiosis. Typically results in miscarriage.
    • Tetraploidy (4n): A cell has four copies of each chromosome, usually due to a failure of the first zygotic cell division. Typically results in miscarriage.

Aneuploidy

  • Aneuploidy is an abnormal chromosome number due to an extra or missing chromosome, not a multiple of the haploid number. This is more severe when affecting autosomes than sex chromosomes.
    • Trisomy: The presence of three copies of an autosome or sex chromosome (2n+1). Examples include Down syndrome (trisomy 21).
    • Monosomy: The absence of a single chromosome (2n-1). Commonly incompatible with survival. Example: Turner syndrome (45,X).

Mixoploidy

  • Mixoploidy involves two or more genetically different cell lineages within an individual. This can result from mosaicism or chimerism.

Structural Aberrations

  • Structural aberrations involve chromosome breakage and subsequent reunion, resulting in a variety of changes in chromosome structure. These changes can be balanced or unbalanced.
    • Deletions (del): Loss of part of a chromosome.
    • Inversions (inv): A segment of a chromosome is reversed in orientation (balanced).
    • Insertions (ins): Insertion of a segment from one chromosome into another (balanced or unbalanced).
    • Duplications (dup): Repetition of a chromosomal segment.
    • Translocations: Transfer of genetic material from one chromosome to another.
      • Reciprocal translocations: Exchange of segments between non-homologous chromosomes.
      • Robertsonian translocations: Fusion of the long arms of two acrocentric chromosomes.
    • Ring chromosomes: A chromosome forms a ring due to breaks and rejoining.

Karyotyping

  • Karyotyping is a technique used to visualize and analyze chromosomes. Chromosomal abnormalities can be identified by looking at chromosome number and structure.
  • Karyotype formulae provide an exact description of chromosomal abnormalities, using a standardized nomenclature. For example, 46,XX (normal female) or 47,XX,+21 (Down syndrome).

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