أسئلة المحاضرة الرابعة جينتكس (قبل التعديل)
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Questions and Answers

What is the significance of karyotyping fetal cells?

  • It aids in diagnosing lung diseases.
  • It can only identify chromosomal abnormalities in males.
  • It helps determine the sex of the fetus and diagnose certain diseases. (correct)
  • It is used exclusively for assessing maternal health.

    • Which of the following is a cause of chromosomal abnormalities?

  • Eating a high-protein diet.
  • Exposure to radiation. (correct)
  • Participation in regular exercise.
  • Drinking herbal tea.

    • What does the term 'Trisomy' refer to?

  • An extra chromosome present in a normal pair. (correct)
  • A complete absence of chromosomes.
  • A condition caused by a viral infection.
  • A structural alteration of chromosomes.

    • What is the primary function of telomeres?

    <p>To stabilize and protect chromosome ends</p> Signup and view all the answers

    What condition is associated with the chromosome count of 47,XXY?

    <p>Klinefelter's syndrome.</p> Signup and view all the answers

    Which syndromes result from monosomy?

    <p>Turner’s syndrome and Wolf syndrome.</p> Signup and view all the answers

    What are the two arms of a chromatid called?

    <p>P and Q arms</p> Signup and view all the answers

    What is a key feature of Turner’s syndrome?

    <p>A missing X chromosome.</p> Signup and view all the answers

    How are metacentric chromosomes characterized?

    <p>Centromere near the middle with arms of equal length</p> Signup and view all the answers

    Which type of chromosome has only one arm?

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

    Which of the following is NOT a type of chromosomal abnormality?

    <p>Hemolytic abnormalities.</p> Signup and view all the answers

    Which viral infection is linked to chromosomal fragmentation?

    <p>German measles.</p> Signup and view all the answers

    How many pairs of autosomes are present in humans?

    <p>22 pairs</p> Signup and view all the answers

    What is the classification of chromosomes based on their total length and centromere position?

    <p>Denver classification</p> Signup and view all the answers

    What is the composition of sex chromosomes in females?

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

    Which group in the Denver classification includes chromosome numbers 1-3?

    <p>Group A</p> Signup and view all the answers

    What happens when an ovum with no X chromosomes is fertilized by sperm with a Y chromosome?

    <p>The resulting zygote will contain X0 chromosomes.</p> Signup and view all the answers

    Which condition is characterized by the deletion of the short arm of chromosome number 5?

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

    What is the term used for the addition of a chromosome to a pair?

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

    What kind of chromosomal alteration is associated with chronic myeloid leukemia?

    <p>Translocation between chromosomes 9 and 22</p> Signup and view all the answers

    Down's syndrome is best described as which of the following?

    <p>Addition of a chromosome to pair 21</p> Signup and view all the answers

    What is a karyotype?

    <p>An analysis of chromosome number and structure</p> Signup and view all the answers

    Which substance is used to stop cell division at metaphase during karyotyping?

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

    What role does phyto-haemagglutinin play in karyotyping?

    <p>It stimulates cell division</p> Signup and view all the answers

    What is the final step in the karyotyping process described?

    <p>Photographed chromosomes are cut and matched into pairs.</p> Signup and view all the answers

    During karyotyping, what occurs after blood is collected and treated with anticoagulant?

    <p>The blood is centrifuged to separate lymphocytes.</p> Signup and view all the answers

    What is the purpose of using a hypotonic solution in the karyotyping process?

    <p>To swell the cells and spread chromosomes apart.</p> Signup and view all the answers

    What fundamental component makes up a chromosome?

    <p>Histones and tightly packed DNA</p> Signup and view all the answers

    In which phase of the cell cycle are cells typically arrested for karyotyping?

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

    What is the primary role of phyto-haemagglutinin in the karyotyping process?

    <p>Stimulates lymphocyte division</p> Signup and view all the answers

    Which step is crucial for halting cell division at metaphase during karyotyping?

    <p>Introduction of colchicine</p> Signup and view all the answers

    What is the purpose of spreading cultured cells on slides using the drop method in karyotyping?

    <p>To evenly distribute chromosomes for examination</p> Signup and view all the answers

    Which of the following accurately describes the structure of a chromosome?

    <p>A tightly packed DNA molecule around histone proteins</p> Signup and view all the answers

    Why is it important to centrifuge blood samples during karyotyping?

    <p>To isolate lymphocytes for analysis</p> Signup and view all the answers

    What is the expected outcome after treating cultured lymphocytes with a hypotonic solution in karyotyping?

    <p>Swelling of cells to enhance chromosome visibility</p> Signup and view all the answers

    In which phase of the cell cycle are lymphocytes typically arrested for karyotyping?

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

    What is the final action taken with the photographed chromosomes during karyotyping?

    <p>Matching into pairs using an image analyser</p> Signup and view all the answers

    What is the primary function of telomeres in chromosomes?

    <p>To stabilize and protect the chromosome ends</p> Signup and view all the answers

    Which type of chromosome has a centromere that divides its arms into two equal lengths?

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

    In which chromosome classification are chromosomes grouped based on both length and centromere position?

    <p>Denver classification</p> Signup and view all the answers

    What is unique about telocentric chromosomes?

    <p>They only have one arm</p> Signup and view all the answers

    Which of the following statements about sex chromosomes is correct?

    <p>Females have one pair of identical homologues.</p> Signup and view all the answers

    What is the primary characteristic of Cri-du-chat syndrome?

    <p>Deletion of the short arm on chromosome number 5</p> Signup and view all the answers

    How many pairs of sex chromosomes are found in humans?

    <p>One pair</p> Signup and view all the answers

    Which statement accurately describes the Philadelphia chromosome?

    <p>It is due to the translocation between chromosomes 9 and 22.</p> Signup and view all the answers

    Which of the following describes the zygote resulting from an ovum without X chromosomes fertilized by sperm with an X chromosome?

    <p>The zygote will have a karyotype of 45 (XO)</p> Signup and view all the answers

    Which type of chromosome has one short and one long arm but is not classified as telocentric?

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

    What effect does trisomy have on chromosome pairs?

    <p>Leads to the addition of an extra chromosome to a pair</p> Signup and view all the answers

    What classification of chromosomes is based on their gene content?

    <p>Karyotypic classification</p> Signup and view all the answers

    The most common form of Down's syndrome is associated with which chromosomal abnormality?

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

    What type of chromosomal abnormality is characterized by an extra chromosome in an individual?

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

    Which of the following conditions is associated with a missing sex chromosome?

    <p>Turner syndrome</p> Signup and view all the answers

    Which factor is NOT associated with increasing the risk of chromosomal abnormalities?

    <p>Male gender</p> Signup and view all the answers

    Klinefelter syndrome results from which specific meiotic error?

    <p>Non-separation of homologous chromosomes</p> Signup and view all the answers

    What specific chromosomal anomaly is indicated by the Philadelphia chromosome?

    <p>A translocation between chromosomes 9 and 22</p> Signup and view all the answers

    Which syndrome results from a deletion of the short arm of chromosome 5?

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

    What is one of the main clinical uses of karyotyping in fetal cells?

    <p>To diagnose certain genetic syndromes</p> Signup and view all the answers

    Which of the following is a characteristic of autosomal anomalies?

    <p>Can involve missing chromosomes or extra chromosomes</p> Signup and view all the answers

    What is the role of colchicine in the karyotyping process?

    <p>Colchicine halts cell division at metaphase, allowing for chromosome analysis.</p> Signup and view all the answers

    Describe the importance of using anticoagulants during the karyotyping procedure.

    <p>Anticoagulants prevent blood from clotting, ensuring that lymphocytes can be separated and cultured.</p> Signup and view all the answers

    Why are lymphocytes used for karyotyping instead of other blood cells?

    <p>Lymphocytes can be stimulated to divide, which makes them suitable for examining chromosomes.</p> Signup and view all the answers

    What is the role of phyto-haemagglutinin in the karyotyping procedure?

    <p>Phyto-haemagglutinin stimulates lymphocyte division, enabling the growth of cells for analysis.</p> Signup and view all the answers

    Explain the purpose of incubating lymphocytes in culture medium during karyotyping.

    <p>Incubation in culture medium supports the growth and division of lymphocytes for chromosome extraction.</p> Signup and view all the answers

    What happens to the cultured lymphocytes after colchicine treatment?

    <p>The cells are treated with a hypotonic solution to spread the chromosomes for visualization.</p> Signup and view all the answers

    How is the karyotype assembled after photographing the chromosomes?

    <p>Photographed chromosomes are cut and matched into pairs using an image analyzer.</p> Signup and view all the answers

    What is the significance of examining chromosomes at metaphase for karyotyping?

    <p>Chromosomes are most condensed and distinct at metaphase, allowing for clearer visualization and analysis.</p> Signup and view all the answers

    What is the karyotype associated with Turner’s syndrome?

    <p>45,XO</p> Signup and view all the answers

    Explain the chromosomal alteration that leads to Cri-du-chat syndrome.

    <p>Cri-du-chat syndrome is caused by a deletion of the short arm of chromosome number 5.</p> Signup and view all the answers

    What type of chromosomal mutation is exemplified by the Philadelphia chromosome?

    <p>Translocation between chromosomes 9 and 22.</p> Signup and view all the answers

    What are the three types of chromosome based on the position of the centromere?

    <p>Metacentric, submetacentric, acrocentric.</p> Signup and view all the answers

    How is Down's syndrome primarily caused in terms of chromosome count?

    <p>It is caused by trisomy 21, which means there is an extra chromosome 21.</p> Signup and view all the answers

    How are the long and short arms of a chromatid referred to?

    <p>The long arm is called the q arm, and the short arm is called the p arm.</p> Signup and view all the answers

    What happens to the chromosomal composition when an ovum with no X chromosomes is fertilized by sperm with an X chromosome?

    <p>The resulting zygote will have an X0 composition.</p> Signup and view all the answers

    What distinguishes an acrocentric chromosome from other types?

    <p>An acrocentric chromosome has one arm significantly shorter than the other, with the centromere close to one end.</p> Signup and view all the answers

    What is the composition of sex chromosomes in male humans?

    <p>Males have one pair of unidentical sex chromosomes, XY.</p> Signup and view all the answers

    Describe the telomeres’ role in chromosome stability.

    <p>Telomeres protect the ends of chromosomes from deterioration and prevent fusion with neighboring chromosomes.</p> Signup and view all the answers

    What classification system divides chromosomes into groups A to G?

    <p>The Denver classification system.</p> Signup and view all the answers

    What are the characteristics of metacentric chromosomes?

    <p>Metacentric chromosomes have a centromere located nearly in the middle, resulting in two arms of equal length.</p> Signup and view all the answers

    How many pairs of homologous autosomes do humans have?

    <p>Humans have 22 pairs of homologous autosomes.</p> Signup and view all the answers

    What is the clinical significance of karyotyping in prenatal diagnosis?

    <p>Karyotyping helps in prenatal diagnosis by detecting chromosomal abnormalities and determining the sex of the fetus.</p> Signup and view all the answers

    Identify two important types of chromosomal abnormalities.

    <p>The two important types of chromosomal abnormalities are numerical abnormalities (like monosomy and trisomy) and structural abnormalities (like deletions or translocations).</p> Signup and view all the answers

    Describe the primary genetic mechanism that results in Klinefelter's syndrome.

    <p>Klinefelter's syndrome is primarily caused by the non-separation of chromosomes during the first meiotic division, leading to an ovum containing two X chromosomes.</p> Signup and view all the answers

    What are the implications of advanced maternal age on chromosomal abnormalities?

    <p>Advanced maternal age can increase the risk of chromosomal abnormalities in offspring, including congenital syndromes due to non-disjunction during meiosis.</p> Signup and view all the answers

    In terms of chromosome count, how does Turner’s syndrome manifest?

    <p>Turner’s syndrome manifests as a missing sex chromosome, resulting in a 45,X chromosomal pattern.</p> Signup and view all the answers

    How does chronic myeloid leukemia relate to chromosomal abnormalities?

    <p>Chronic myeloid leukemia is associated with a specific chromosomal abnormality known as the Philadelphia chromosome, which results from a translocation between chromosomes 9 and 22.</p> Signup and view all the answers

    What role does radiation play in inducing chromosomal damage?

    <p>Radiation can lead to chromosomal damage by causing breaks in the DNA structure, which may result in abnormalities such as deletions or translocations.</p> Signup and view all the answers

    What is the significance of identifying the sex of a fetus through karyotyping?

    <p>Identifying the sex of a fetus via karyotyping is significant for understanding potential sex-linked genetic disorders and making informed medical decisions.</p> Signup and view all the answers

    What is the purpose of adding colchicine during the karyotyping process?

    <p>Colchicine is added to halt cell division at metaphase, allowing chromosomes to be visualized.</p> Signup and view all the answers

    Explain the role of anticoagulants like heparin in karyotyping.

    <p>Anticoagulants prevent blood from clotting, enabling the separation of lymphocytes for analysis.</p> Signup and view all the answers

    Describe the significance of using a hypotonic solution in the karyotyping procedure.

    <p>A hypotonic solution causes lymphocytes to swell, facilitating the spreading of chromosomes on slides.</p> Signup and view all the answers

    What is the primary benefit of using phyto-haemagglutinin in the karyotyping process?

    <p>Phyto-haemagglutinin stimulates lymphocyte division, promoting a sufficient number of cells for analysis.</p> Signup and view all the answers

    Identify the main structural component of chromosomes and its significance.

    <p>Chromosomes are primarily composed of tightly coiled DNA around histone proteins, which help in DNA packaging.</p> Signup and view all the answers

    What is the final action performed with the photographed chromosomes after karyotyping?

    <p>The photographed chromosomes are cut and matched into pairs using an image analyzer.</p> Signup and view all the answers

    Explain the significance of using a culture medium during lymphocyte preparation for karyotyping.

    <p>The culture medium provides nutrients and an environment that supports lymphocyte growth and division.</p> Signup and view all the answers

    How does karyotyping help in understanding genetic disorders?

    <p>Karyotyping allows for the detection of chromosomal abnormalities that can lead to genetic disorders.</p> Signup and view all the answers

    What chromosomal abnormality is primarily linked to advanced maternal age during pregnancy?

    <p>Increased risk of Down syndrome.</p> Signup and view all the answers

    Discuss the impact of non-separation of chromosomes during meiosis on Klinefelter's syndrome.

    <p>Non-separation leads to the formation of an ovum with two X chromosomes, resulting in the 47,XXY condition.</p> Signup and view all the answers

    How is Turner’s syndrome caused at the chromosomal level?

    <p>Turner’s syndrome results from a missing X chromosome, leading to a 45,X karyotype.</p> Signup and view all the answers

    What is the genetic basis for chronic myeloid leukemia?

    <p>It is often associated with the Philadelphia chromosome due to a translocation.</p> Signup and view all the answers

    Identify a viral infection that can lead to chromosomal fragmentation and outline its effect.

    <p>German measles can cause fragmentation of chromosomes, leading to potential genetic abnormalities.</p> Signup and view all the answers

    Explain what monosomy is and provide an example of a syndrome associated with it.

    <p>Monosomy refers to the absence of one chromosome in a pair; an example is Turner’s syndrome.</p> Signup and view all the answers

    What are the two main types of chromosomal abnormalities and give an example of each.

    <p>The two types are numerical (e.g., trisomy) and structural (e.g., deletion).</p> Signup and view all the answers

    Discuss the significance of karyotyping in prenatal diagnosis.

    <p>Karyotyping helps identify chromosomal abnormalities in fetal cells, aiding in prenatal care and disease diagnosis.</p> Signup and view all the answers

    What chromosome composition is found in Turner's syndrome and what are its potential clinical implications?

    <p>Turner's syndrome is characterized by a 45,X karyotype, which can lead to developmental and reproductive issues such as short stature and infertility.</p> Signup and view all the answers

    What specific chromosomal alteration occurs in Cri-du-chat syndrome and what are its distinctive features?

    <p>Cri-du-chat syndrome is caused by a deletion of the short arm of chromosome 5, characterized by a distinctive cat-like cry in affected infants.</p> Signup and view all the answers

    Explain the chromosomal composition of a zygote resulting from the fertilization of an ovum with no X chromosome by sperm carrying an X chromosome.

    <p>The resulting zygote will have an X0 karyotype, which is indicative of Turner’s syndrome.</p> Signup and view all the answers

    Discuss the significance of Philadelphia chromosomes in a clinical context.

    <p>Philadelphia chromosomes result from a translocation between chromosomes 9 and 22, commonly associated with chronic myeloid leukemia (CML).</p> Signup and view all the answers

    Describe the concept of trisomy and its most common example, including its chromosomal basis.

    <p>Trisomy refers to the presence of three copies of a particular chromosome; the most common example is Down's syndrome, or trisomy 21, which involves three copies of chromosome 21.</p> Signup and view all the answers

    Which structures at the ends of chromosomes serve to stabilize and protect them?

    <p>Telomeres.</p> Signup and view all the answers

    Describe the relationship between chromatids and the centromere in a human chromosome.

    <p>Each chromosome consists of two identical chromatids connected at the centromere.</p> Signup and view all the answers

    What distinguishes submetacentric chromosomes from metacentric chromosomes?

    <p>Submetacentric chromosomes have one longer arm while metacentric chromosomes have arms of equal length.</p> Signup and view all the answers

    How many pairs of homologous chromosomes are classified as autosomes in humans?

    <p>There are 22 pairs of homologous autosomes.</p> Signup and view all the answers

    Identify the chromosome groups in the Denver classification that include chromosomes 19-20.

    <p>Group F.</p> Signup and view all the answers

    In the context of chromosomal classification, what do the terms 'P arm' and 'q arm' refer to?

    <p>The 'P arm' is the short arm, while the 'q arm' is the long arm of a chromatid.</p> Signup and view all the answers

    What classification does the X chromosome belong to in terms of gene complement?

    <p>The X chromosome is classified as a sex chromosome.</p> Signup and view all the answers

    What feature is characteristic of telocentric chromosomes?

    <p>Telocentric chromosomes have a centromere located at one end, resulting in only one arm.</p> Signup and view all the answers

    Study Notes

    Karyotype and Chromosome Analysis

    • A karyotype is a description of the number and structure of chromosomes.
    • Karyotyping is carried out in dividing cells halted in metaphase.
    • The process involves culturing lymphocytes, stimulating their division, then arresting them in metaphase using colchicine.
    • Chromosomes are then fixed, stained, examined, and photographed.
    • Photographed chromosomes are matched into pairs.

    Chromosome Structure

    • Chromosomes are thread-like structures containing DNA tightly packed and coiled around histones.
    • Telomeres are repetitive nucleotide sequences located at each end of a chromosome.
    • Telomeres stabilize and protect chromosome ends from deterioration or fusion.
    • Each chromosome is composed of two identical chromatids connected at the centromere.
    • Each chromatid has a long arm (q arm) and a short arm (p arm).

    Chromosome Classification

    • By centromere position:
      • Metacentric: Centromere is in the middle, arms are equal in length.
      • Submetacentric: Centromere is between the center and the end, one arm is longer than the other.
      • Acrocentric: Centromere is close to one end, one arm is much shorter.
      • Telocentric: Centromere is at the end, only one arm is present (not in humans).
    • By gene complement:
      • Autosomes: 22 pairs of identical homologous chromosomes.
      • Sex chromosomes: One pair of either identical homologues (XX, female) or unidentical homologues (XY, male).
    • Denver classification:
      • Groups chromosomes based on length and centromere position into seven groups (A-G) in descending order.

    Clinical Importance of Chromosomal Studies

    • Diagnosis of diseases and syndromes such as Down syndrome.
    • Diagnosis of malignant diseases like chronic myeloid leukemia.
    • Prenatal diagnosis of diseases and determination of fetal sex.

    Causes of Chromosomal Abnormalities

    • Radiation can cause chromosomal damage.
    • Family history of chromosomal abnormalities.
    • German measles infection can fragment chromosomes.
    • Pregnancy in older women can lead to congenital syndromes.
    • Autoimmune diseases can cause chromosomal abnormalities.

    Types of Chromosomal Abnormalities

    • Numerical: Abnormal number of chromosomes:
      • Monosomy: One chromosome missing.
      • Trisomy: One extra chromosome.
    • Structural: Part of a chromosome is missing, extra, or switched to another chromosome.

    Specific Chromosomal Abnormalities

    • Klinefelter's syndrome: 47,XXY
      • Non-separation of chromosomes in the first meiotic cell division in the mother during ova formation.
      • Ova contains two X chromosomes.
      • Fertilization by a Y sperm results in XXY chromosomes.
    • Turner's syndrome: 45,X0
      • Non-separation of chromosomes in the first meiotic cell division in the mother during ova formation.
      • Ova contains no X chromosomes.
      • Fertilization by an X sperm results in X0 chromosomes.
    • Down's syndrome (Trisomy 21):
      • Most common trisomy.
      • An extra chromosome 21.
    • Cri-du-chat syndrome: Deletion of the short arm on chromosome 5.
      • Characterized by a cat-like cry in infants.
    • Wolf syndrome: Deletion of the short arm on chromosome 4.
    • Philadelphia chromosome: Translocation between chromosomes 9 and 22.
      • Occurs in chronic myeloid leukemia.

    Karyotyping

    • Karyotyping is the process of examining and describing the number and structure of chromosomes in a cell.
    • The analysis is performed on cells in metaphase of the cell cycle.
    • To obtain cells for analysis, a blood sample is collected and treated with an anticoagulant like heparin.
    • Lymphocytes are separated from other cells in the blood by centrifugation.
    • Lymphocytes are stimulated to divide by adding a mitogenic agent, phytohemagglutinin to the culture medium.
    • Cell division is stopped at metaphase by adding colchicine.
    • The cells are then treated with a hypotonic solution which causes them to swell.
    • Finally, cells are spread on slides by the drop method and stained for analysis.

    Chromosomes

    • Chromosomes are thread-like structures located in the nucleus of eukaryotic cells that contain DNA.
    • DNA is tightly coiled around a protein called histones.
    • Telomeres are regions of repetitive nucleotide sequences located at the ends of chromosomes.
    • Telomeres help stabilize and protect the ends of chromosomes from deterioration and fusion.

    Structure of Human Chromosomes

    • Each chromosome is composed of two identical chromatids joined by a centromere.
    • Each chromatid has a long arm (q) and a short arm (p).
    • The terminal ends of each chromatid are called telomeres.

    Chromosome Classification

    Classification By Centromere Position

    • Metacentric: Centromere is located in the middle of the chromosome and both arms are the same length.
    • Submetacentric: Centromere is slightly off center and results in one arm being slightly longer than the other.
    • Acrocentric: Centromere is located near one end of the chromosome, making one arm much shorter than the other.
    • Telocentric: Centromere is located at the end of the chromosome with only one arm. Telocentric chromosomes are NOT found in humans.

    Classification By Gene Complement

    • Autosomes: 22 pairs of chromosomes that are identical in males and females.
    • **Sex Chromosomes:**One pair of chromosomes that determine sex.
      • XX - Female
      • XY - Male

    Denver Classification

    • Chromosomes are classified into seven groups based on length and centromere position.
    • Groups are organized in descending order from largest to smallest.
    • Group A: Chromosomes 1-3 (Largest)
    • Group B: Chromosomes 4-5 and the X chromosome
    • Group C: Chromosomes 6-12
    • Group D: Chromosomes 13-15
    • Group E: Chromosomes 16-18
    • Group F: Chromosomes 19-20 and the Y chromosome
    • Group G: Chromosomes 21-22 (Smallest)

    Clinical Importance of Karyotyping

    • Karyotyping is used to diagnose genetic diseases and syndromes.
    • It can be used to diagnose cancers like Chronic Myeloid Leukemia (CML).
    • Fetal karyotyping can aid in prenatal diagnosis of genetic diseases and determine the sex of the fetus.

    Causes of Chromosomal Abnormalities

    • Radiation exposure can cause chromosomal damage.
    • Family history of chromosomal abnormalities can increase the risk.
    • Infections like German measles can cause chromosomal fragmentation.
    • Pregnancy in older women is associated with a higher risk of chromosomal abnormalities.
    • Autoimmune diseases can also lead to chromosomal abnormalities.

    Types of Chromosomal Abnormalities

    • Numerical Abnormalities: Involve an abnormal number of chromosomes
      • Monosomy: One chromosome is missing from a pair.
      • Trisomy: One extra chromosome is present in a pair.
    • Structural Abnormalities: Involve the structure of a chromosome.
      • Deletion: A part of a chromosome is missing.
      • Translocation: A part of a chromosome has been switched to another chromosome.

    Examples of Chromosomal Abnormalities

    • Sex Chromosome Abnormalities*
    • Klinefelter's Syndrome: 47, XXY (Male - extra X chromosome)
    • Turner's Syndrome: 45, XO (Female - missing X chromosome)
    • Autosomal Abnormalities*
    • Down Syndrome (Trisomy 21): 47, XX or XY +21 (Male or Female - extra chromosome 21)
    • Wolf Syndrome: Deletion in the short arm of chromosome 4.
    • Cri-du-chat Syndrome: Deletion of the short arm on chromosome 5.
    • Philadelphia Chromosome: A translocation between chromosomes 9 and 22 associated with chronic myeloid leukemia (CML).

    Karyotyping

    • Karyotyping is the process of analyzing and describing the number and structure of chromosomes.
    • It is typically carried out in dividing cells arrested in the metaphase stage of cell division.

    Karyotyping Procedure

    • A blood sample is collected and anticoagulant (heparin) is added.
    • Blood is centrifuged to separate lymphocytes from other cells.
    • Lymphocytes are incubated in a suitable culture medium, with phyto-haemagglutinin (mitogenic agent) added to stimulate division.
    • Cultured lymphocytes are incubated for three days.
    • Colchicine is added to stop cell division at metaphase.
    • Cells are treated with a hypotonic solution.
    • Samples are spread on slides using the drop method.
    • Chromosomes are fixed, stained, examined, and photographed.
    • Photographed chromosomes are cut and matched into pairs using an image analyzer.

    Chromosome Structure

    • Chromosomes are thread-like structures composed of DNA tightly packed and coiled around histones.
    • Telomeres are regions of repetitive nucleotide sequences located at each end of a chromosome.
    • Telomeres stabilize and protect chromosome ends from deterioration and fusion with neighboring chromosomes.
    • Each chromosome is formed of two identical chromatids connected at the centromere.
    • Each chromatid has:
      • A long arm called the "q" arm.
      • A short arm called the "p" arm.

    Chromosome Classification

    By Centromere Position

    • Metacentric: Centromere is nearly in the middle, resulting in two arms of the same length.
    • Submetacentric: Centromere is between the center and upper ends, resulting in one arm longer than the other.
    • Acrocentric: Centromere is close to one end, resulting in one arm much shorter than the other.
    • Telocentric: Centromere is at the end, resulting in only one arm (not present in humans).

    By Gene Complement

    • Autosomes (somatic): 22 pairs of identical homologues.
    • Sex chromosomes: One pair of chromosomes:
      • Identical homologues (XX) in females.
      • Unidentical homologues (XY) in males.

    Denver Classification

    • Groups chromosomes based on their total length and centromere position in descending order:
    Group Chromosome Number Features
    A 1-3
    B 4-5, X chromosome
    C 6-12
    D 13-15
    E 16-18
    F 19-20, Y chromosome
    G 21-22

    Clinical Importance of Chromosomal Studies

    • Diagnosis of diseases and syndromes:
      • Down syndrome.
    • Diagnosis of malignant diseases:
      • Chronic myeloid leukemia.
    • Prenatal diagnosis:
      • Detecting certain diseases and determining fetal sex.

    Causes of Chromosomal Abnormalities

    • Radiation: Can cause chromosomal damage.
    • Family history: Parents or family members with chromosomal abnormalities increase the risk.
    • German measles infection: The virus can fragment chromosomes.
    • Older maternal age: Increases the risk of children with congenital syndromes.
    • Autoimmune diseases: Can cause chromosomal abnormalities.

    Types of Chromosomal Abnormalities

    Numerical Abnormalities

    • Abnormal number of chromosomes:
      • Monosomy: Missing a chromosome.
      • Trisomy: An extra chromosome in a normal pair.

    Structural Abnormalities

    • Alterations in chromosome structure:
      • Deletion: Part of a chromosome is missing.
      • Translocation: Exchange of material between non-homologous chromosomes.

    Examples of Chromosomal Abnormalities

    Numerical Abnormalities

    Sex Chromosomes
    • Klinefelter’s syndrome (47,XXY): Non-separation of chromosomes in the mother during the formation of ova, resulting in an ovum with two X chromosomes (XX). Fertilization by a sperm with a Y chromosome leads to a zygote with XXY chromosomes.
    • Turner’s syndrome (45,XO): Non-separation of chromosomes in the mother during the formation of ova, resulting in an ovum with no X chromosomes. Fertilization by a sperm with an X chromosome leads to a zygote with XO chromosomes.
    Autosomes
    • Monosomy: Wolf syndrome (missing part of chromosome 4).
    • Trisomy: Down syndrome (trisomy 21).

    Structural Abnormalities

    • Deletion:
      • Cri-du-chat syndrome: Deletion of the short arm on chromosome 5, characterized by a cat-like cry in affected infants.
    • Translocation:
      • Philadelphia chromosome: Translocation between chromosomes 9 and 22, often observed in chronic myeloid leukemia.

    Karyotyping

    • Karyotyping is the description of the number and structure of chromosomes
    • Karyotyping is performed on dividing cells arrested in metaphase

    Karyotyping Procedure

    • Collect blood sample
    • Add anticoagulant like heparin
    • Centrifuge blood to separate lymphocytes
    • Incubate lymphocytes in a suitable medium
    • Add phyto-haemagglutinin to stimulate division
    • Culture for 3 days
    • Stop cell division with colchicine
    • Treat cultured cells with hypotonic solution
    • Spread cells on slides using the drop method
    • Fix, stain and examine chromosomes
    • Photograph chromosomes and cut, then match pairs with image analyser

    Chromosomes

    • Thread-like structures
    • Consists of DNA molecule tightly packed and coiled around histones

    Telomere

    • Region of repetitive nucleotide sequences at each end of a chromosome
    • Stabilizes and protects chromosomes from deterioration and fusion

    Structure of Human Chromosome

    • Each chromosome is formed of two identical chromatids connected at their centromere
    • Each chromatid has a long arm (q) and a short arm (p)
    • Telomeres are the terminal ends of the chromatids

    Chromosome Classification (based on position of centromere)

    • Metacentric: Centromere is nearly in the middle, two arms are of equal length
    • Submetacentric: Centromere is between the center and the upper end, one arm is longer than the other
    • **Acrocentric:**Centromere is close to one end, one arm is much shorter than the other
    • Telocentric: Centromere is at the end, only one arm (not present in humans)

    Chromosome Classification (based on gene complement)

    • Autosomes (somatic): 22 pairs of identical homologues
    • Sex chromosomes: One pair of
      • Identical homologues (XX female)
      • Unidentical homologues (XY male)

    Denver Classification

    • Based on length and position of centromere into 7 groups in descending order:
      • Group A: Chromosomes 1-3
      • Group B: Chromosomes 4-5 and X chromosome
      • Group C: Chromosomes 6-12
      • Group D: Chromosomes 13-15
      • Group E: Chromosomes 16-18
      • Group F: Chromosomes 19-20 and Y chromosome
      • Group G: Chromosomes 21-22

    Clinical Importance of Chromosomal Studies

    • Diagnosis of diseases:
      • Down syndrome
      • Chronic myeloid leukemia
    • Prenatal diagnosis:
      • Diagnose diseases
      • Determine fetal sex

    Causes of Chromosomal Abnormalities

    • Radiation: causes chromosomal damage
    • Family history: hereditary factors
    • German measles: virus causes fragmentation of chromosomes
    • Pregnancy in older women: may result in children with congenital syndromes
    • Auto-immune diseases: can cause chromosomal abnormalities

    Types of Chromosomal Abnormalities

    • Numerical: Abnormal number of chromosomes
      • Monosomy: Missing chromosome
      • Trisomy: Extra chromosome
    • Structural: Part of an individual chromosome is missing, extra, or switched to another chromosome

    Sex Chromosome Abnormalities

    • Males:
      • Klinefelter’s syndrome (47, XXY): Non-separation of chromosomes occurs during the first meiotic cell division in the mother during the formation of ova, resulting in an ovum with two X chromosomes. Fertilization with a sperm containing a Y chromosome results in XXY chromosomes
    • Females:
      • Turner's syndrome (45, XO): Non-separation of chromosomes occurs during the first meiotic cell division in the mother during the formation of ova, resulting in an ovum with no X chromosomes. Fertilization with a sperm containing an X chromosome leads to XO chromosomes

    Autosome Abnormalities

    • Monosomy: Wolf syndrome
    • Trisomy: Down's syndrome
    • Structural: Cri-du-chat syndrome, Philadelphia chromosome

    Down's Syndrome (Mongolism or Trisomy 21)

    • Most common chromosomal abnormality
    • Trisomy 21: the addition of a chromosome to the pair
    • Characterized by certain physical features and developmental delays

    Deletion

    • Detachment and loss of portions from chromosomal arms
    • Cri-du-chat syndrome: Deletion of the short arm on chromosome number 5, characterized by a cat-like cry in babies
    • Wolf syndrome: Deletion of the short arm on chromosome number 4

    Translocation

    • Exchange of material between non-homologous chromosomes
    • Philadelphia chromosome: Translocation between chromosomes 9 and 22, commonly found in Chronic Myeloid Leukemia

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