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Questions and Answers
What is the term used to describe a chromosome complement with any number other than 46?
What is the term used to describe a chromosome complement with any number other than 46?
Which of the following types of chromosomal abnormalities usually have no phenotypic effect?
Which of the following types of chromosomal abnormalities usually have no phenotypic effect?
What is the term used to describe the failure of a pair of chromosomes to disjoin properly during one of the two meiotic divisions?
What is the term used to describe the failure of a pair of chromosomes to disjoin properly during one of the two meiotic divisions?
What is the term used to describe a condition in which there is an extra or missing chromosome?
What is the term used to describe a condition in which there is an extra or missing chromosome?
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What is the term used to describe a chromosome that has an extra copy of a particular chromosome?
What is the term used to describe a chromosome that has an extra copy of a particular chromosome?
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What is the term used to describe a condition in which there is only one copy of a particular chromosome?
What is the term used to describe a condition in which there is only one copy of a particular chromosome?
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What is the term used to describe a condition in which an individual has two or more different chromosome complements?
What is the term used to describe a condition in which an individual has two or more different chromosome complements?
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What is the term used to describe a type of translocation in which two acrocentric chromosomes fuse near the centromere region with loss of the short arms?
What is the term used to describe a type of translocation in which two acrocentric chromosomes fuse near the centromere region with loss of the short arms?
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What is the main focus of clinical cytogenetics?
What is the main focus of clinical cytogenetics?
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What is the term used to describe microscopically visible changes in the number or structure of chromosomes?
What is the term used to describe microscopically visible changes in the number or structure of chromosomes?
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What is the result of a nondisjunction event during meiosis?
What is the result of a nondisjunction event during meiosis?
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What is the term used to describe a condition where a cell has an extra copy of a chromosome?
What is the term used to describe a condition where a cell has an extra copy of a chromosome?
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What is the term used to describe a condition where a cell is missing a copy of a chromosome?
What is the term used to describe a condition where a cell is missing a copy of a chromosome?
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What is the purpose of collecting a sample of peripheral blood in cytogenetic analysis?
What is the purpose of collecting a sample of peripheral blood in cytogenetic analysis?
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What is the purpose of using a hypotonic solution in cytogenetic analysis?
What is the purpose of using a hypotonic solution in cytogenetic analysis?
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What is the result of chromosome abnormalities?
What is the result of chromosome abnormalities?
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Why are chromosomes fixed and stained in cytogenetic analysis?
Why are chromosomes fixed and stained in cytogenetic analysis?
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What is the approximate spontaneous abortion rate?
What is the approximate spontaneous abortion rate?
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What determines the expression of a disease phenotype in genomic imprinting?
What determines the expression of a disease phenotype in genomic imprinting?
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During which stage of development does genomic imprinting take place?
During which stage of development does genomic imprinting take place?
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What is the result of genomic imprinting on gene expression?
What is the result of genomic imprinting on gene expression?
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What persists postnatally into adulthood through hundreds of cell divisions?
What persists postnatally into adulthood through hundreds of cell divisions?
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What governs the conversion process of genomic imprinting?
What governs the conversion process of genomic imprinting?
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What is the term for the presence of an extra chromosome in a cell?
What is the term for the presence of an extra chromosome in a cell?
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What is the term for the presence of three copies of a chromosome in a cell?
What is the term for the presence of three copies of a chromosome in a cell?
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Study Notes
Molecular Karyotyping
- Molecular karyotyping is the application of genomic techniques to assess the integrity and dosage of the karyotype genome-wide.
- Determining the most appropriate approach for diagnostic or research purposes is a rapidly evolving area.
Clinical Indications for Chromosome Analysis
- Problems of early growth and development
- Stillbirth and neonatal death
- Fertility problems
- Family history
- Neoplasia
- Pregnancy in a woman of advanced age
Tissue Sampling
- Skin biopsy: a minor surgical procedure that provides samples of tissue that can produce fibroblasts in culture.
- White blood cells can be transformed in culture to form lymphoblastoid cell lines that are potentially immortal.
- Bone marrow: obtained only by a relatively invasive procedure of marrow biopsy.
- Fetal cells: derived from amniotic fluid (amniocytes) or obtained by chorionic villus biopsy.
Chromosome Abnormalities
- Numerical or structural abnormalities: involve one or more autosomes, sex chromosomes, or both simultaneously.
- Aneuploidy: abnormal chromosome number due to an extra or missing chromosome, always associated with physical or mental maldevelopment or both.
- Reciprocal translocations: an exchange of segments between nonhomologous chromosomes, relatively common but usually have no phenotypic effect, may increase the risk of abnormal offspring.
Abnormalities of Chromosome Number
- Heteroploidy: a chromosome complement with any number other than 46.
- Euploidy: an exact multiple of the haploid chromosome number (N).
- Aneuploidy: any other chromosome number.
- Triploidy and Tetraploidy: 3N or 4N, e.g., 92,XXXX or 92,XXYY.
Triploidy and Tetraploidy
- Triploid infants can be liveborn but do not survive long.
- Triploidy is observed in 1% to 3% of recognized conceptions, often resulting from fertilization by two sperm (dispermy).
Aneuploidy
- Trisomy: three instead of the normal pair of a particular chromosome.
- Monosomy: only one representative of a particular chromosome.
- Aneuploidy affects 5% of all clinically recognized pregnancies.
- Trisomy 21 is the most common type of trisomy in liveborn infants.
- Karyotype: 47,XX or XY,+21.
Nondisjunction
- Failure of a pair of chromosomes to disjoin properly during meiosis or mitosis.
- Results in aneuploidy, such as trisomy 21.
Abnormalities of Chromosome Structure
- Less common than aneuploidy, occurring in 1 in 375 newborns.
- Chromosome rearrangement occurs spontaneously at a low frequency.
- May be induced by breaking agents such as ionizing radiation, viral infections, and chemicals.
Types of Abnormalities of Chromosome Structure
- Balanced: no genetic material is lost or gained.
- Unbalanced: genetic material is lost or gained, resulting in abnormality.
- Deletions: loss of a chromosome segment.
- Duplications: duplication of a chromosome segment.
- Marker chromosomes: very small, unidentified chromosomes.
- Ring chromosomes: formed when a chromosome undergoes two breaks and the broken ends reunite in a ring structure.
- Isochromosomes: a chromosome with one arm missing (partial monosomy) and the other duplicated in a mirror-image fashion (partial trisomy).
- Dicentric chromosomes: a rare type of abnormal chromosome formed by the fusion of two chromosome segments, each with a centromere.
Balanced Rearrangements
- Do not usually have a phenotypic effect if they are balanced.
- Inversions: a type of balanced rearrangement where a segment of a chromosome is reversed.
- Translocations: a type of balanced rearrangement where a segment of a chromosome is exchanged with a segment of another chromosome.
- Insertions: a type of balanced rearrangement where a segment of a chromosome is inserted into a nonhomologous chromosome.
Mosaicism
- The presence of two or more different chromosome complements in an individual.
- Can result from nondisjunction in an early postzygotic mitotic division.
- Mosaicism can be detected by conventional karyotyping, interphase FISH analysis, or array CGH.
Incidence of Chromosome Anomalies
- Three autosomal trisomies: trisomy 21, trisomy 18, and trisomy 13.
- Four types of sex chromosomal aneuploidy: Turner syndrome (usually 45,X), Klinefelter syndrome (47,XXY), 47,XYY, and 47,XXX.
- Triploidy and tetraploidy account for a small percentage of cases, particularly in spontaneous abortions.
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Description
This quiz covers the application of genomic techniques to assess the integrity and dosage of the karyotype, including clinical indications for chromosome analysis. It explores the determination of approaches for diagnostic or research purposes.
