Cytogenetics Overview Quiz

Cytogenetics

• Cytogenetics is the study of chromosome structure and properties, chromosomal behavior during mitosis and meiosis, chromosome influence on the phenotype, and the factors causing chromosomal changes
• Hare and Singh (1979) described cytogenetics.

Objectives of Lecture

• Define cytogenetics
• Differentiate between karyotype and ideogram
• Interpret normal human karyotype
• List the steps of karyotyping
• Understand the clinical importance of karyotyping
• Classify human chromosomes
• Outline chromosomal abnormalities
• List different forms of numerical chromosomal aberrations
• Understand the mechanisms of numerical aberrations
• Identify clinical syndromes related to numerical aberrations
• Interpret abnormal forms of human karyotypes

Mitotic Chromosomes

• Cytogenetic methods for identifying chromosomal abnormalities linked to birth defects usually involve analyzing mitotic chromosomes.

Analyzing Chromosomes and Genes

• Analyzing chromosomes and genes is crucial for detecting genetic abnormalities that can range from mild, such as vitamin deficiencies or food allergies, to severe conditions like cancer, birth defects, and infant mortality.
• Genetic errors can arise from deletions, insertions of DNA, abnormal numbers of chromosomes or genes, and even single base misplacement within genes.

Studying Human Chromosomes

• Studying human chromosomes uses two main methods:
• Conventional methods (banding techniques, karyotyping): Geimsa staining, Q-banding (quinacrine fluorescence staining), R-banding, and C-banding (centromere staining).
• Advanced methods (molecular techniques, Fluorescence in situ hybridization (FISH)): Advanced techniques using fluorescence for location specific analysis

Karyotype, Karyotyping and Ideogram

• Karyotype: A particular characteristic that identifies and describes a set of chromosomes.
• Karyotype characteristics:
• Chromosome number
• Relative size of different chromosomes
• Position of the centromere
• Length of chromosomal arms
• Presence of secondary constrictions and satellites
• Banding pattern of chromosomes
• Features of sex chromosomes
• Karyotyping: A laboratory process used for chromosomal analysis, frequently used as a routine method for this analysis.
• Ideogram: A diagrammatic representation of the karyotype, showing all chromosome pairs arranged by order of size.

Karyotyping Technique

• Blood sample is collected and processed to isolate and separate chromosomes.
• Specific treatments are used to stimulate mitosis, arrest cells in metaphase, and separate chromosomes.
• Cells are analyzed on microscope slides for abnormal chromosome numbers, arrangements, and structures.
• Photographs of chromosomes are examined to identify abnormalities in chromosome structure and arrange them by size after appropriate staining.

Clinical Importance of Chromosomal Examination

• Diagnosis of sex: Determining sex during fetal development, managing cases of intersex conditions, verifying sex for competitive sports (e.g., female athletes).
• Diagnosis of infertility, miscarriage, and repeated abortion: Investigating infertility and birth defects issues, identifying genetic causes of miscarriages and other reproductive issues.
• Diagnosis of cancers and blood disorders: Identifying genetic factors linked to these conditions for proper diagnosis and management.
• Diagnosis of chromosomal aberrations (numerical and structural abnormalities): Identifying genetic imbalances with respect to chromosome number and structural abnormalities, important aspect of medical diagnosis for various medical conditions.

Normal Male and Female Karyotype

• Illustrations of normal male and female karyotypes.
• Shows pairs of matched chromosomes arranged in descending order of length.
• Includes identifying characteristics like chromosome number and sex chromosomes.

Chromosomal Abnormalities (Aberrations)

• Abnormalities refer to deviations from the usual number or structure of chromosomes.
• They can arise in autosomes or allosomes (sex chromosomes).
• Often result in developmental and mental retardation in individuals.

Causes of Chromosomal Abnormalities

• Radiation
• Viral infections (e.g., rubella)
• Advanced maternal age
• Cytotoxic drugs and autoimmune diseases

Two Chromosomal Abnormalities

• Polyploidy: extra chromosome sets
• Aneuploidy: extra or missing chromosome
• Monosomy: missing chromosome
• Trisomy: extra chromosome
• Duplication: repeating part of a chromosome
• Deletion: missing part of a chromosome
• Translocation: exchange of parts between chromosomes
• Inversion: reversed segment of a chromosome
• Isochromosome: identical arms of a chromosome
• Ring chromosome: ring due to deletions in telomeres.

Abnormal Chromosome Number (Numerical Aberration)

• Euploidy: Exact multiple of haploid number, exceeds diploid number
• Examples: triploid (3n), tetraploid (4n), polyploid, (5n, 6n..).
• Aneuploidy: Not a multiple of the basic haploid number, adds or loses a chromosome:
• Examples: trisomy (extra), monosomy (loss).

Euploidy vs. Aneuploidy

• Distinguishes between euploidy (complete set changes) and aneuploidy (specific chromosome changes).
• Explains causes of these deviations, involving errors during meiosis (nondisjunction errors).
• Describes the effects on different organisms, and clinical consequences.

Genetic Basis of Aneuploidy Nondisjunction

• Nondisjunction: when homologous chromosomes or sister chromatids fail to separate properly during meiosis (I or II).
• Causes: Common occurrences resulting from old maternal age, misalignment, incomplete synapsis, and disrupted spindle function.

Genetic Basis of Aneuploidy (Continued)

• Describes the consequences of nondisjunction occurring in meiosis I versus meiosis II.
• During fertilization, the various combinations of normal versus abnormal gametes explain the resulting outcome (trisomy, monosomy).

Numerical Aberrations (Autosomes and Sex Chromosomes)

• Autosomes: Trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), trisomy 13 (Patau syndrome).
• Sex chromosomes: Triple X syndrome, Klinefelter syndrome (XXY), Turner syndrome (XO).

Nondisjunction in Meiosis I and II

• Illustrates mechanisms of nondisjunction during meiosis I and II.
• Shows the different chromosome outcomes after meiosis I versus meiosis II.

Specific Trisomy Syndromes

• Presents detailed clinical features (e.g., Down syndrome, Edwards syndrome, Patau syndrome) with descriptions of specific physical characteristics, developmental delays and mental retardation.

Specific Monosomy Syndrome

• Detailed clinical presentation of Turner syndrome (XO) with descriptions of specific growth and reproductive features.

Klinefelter Syndrome

• Characteristics (47XXY) and phenotype.

Triple X Syndrome

• Characteristics (47XXX) and phenotype

Numerical Change of Chromosomes

• Illustrates classifications of numerical chromosome changes using a diagram separating euploidy from aneuploidy and related terms. Includes monoploidy, diploidy, triploidy, tetraploidy and poly ploidy.

Test your knowledge on cytogenetics with this quiz, which covers essential concepts like karyotyping, chromosomal aberrations, and G banding techniques. Perfect for students studying genetics or related fields, this quiz will challenge your understanding of chromosome structure and function.