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Questions and Answers
R-bands are obtained by the G-staining methods.
R-bands are obtained by the G-staining methods.
False
C-banding methods can identify every chromosome in the somatic cell complement.
C-banding methods can identify every chromosome in the somatic cell complement.
False
Q-bands are used to reveal constitutive heterochromatin.
Q-bands are used to reveal constitutive heterochromatin.
False
X-chromatin appears as a distinctive structure in interphase nuclei.
X-chromatin appears as a distinctive structure in interphase nuclei.
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Chromosomes in the human somatic cell complement have unbanded areas.
Chromosomes in the human somatic cell complement have unbanded areas.
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T-bands are used to demonstrate patterns of DNA replication.
T-bands are used to demonstrate patterns of DNA replication.
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Y-chromatin appears as a distinctive structure in interphase nuclei.
Y-chromatin appears as a distinctive structure in interphase nuclei.
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R-bands are used to reveal nucleolus organizing regions.
R-bands are used to reveal nucleolus organizing regions.
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The length of each chromosome is expressed as a percentage of the total length of a normal diploid set.
The length of each chromosome is expressed as a percentage of the total length of a normal diploid set.
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The arm ratio of the chromosomes is expressed as the length of the shorter arm to the whole length of the chromosome.
The arm ratio of the chromosomes is expressed as the length of the shorter arm to the whole length of the chromosome.
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The centromeric index is expressed as the ratio of the length of the shorter arm to the whole length of the chromosome.
The centromeric index is expressed as the ratio of the length of the shorter arm to the whole length of the chromosome.
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Bands that stain darkly with one method may stain lightly with other methods.
Bands that stain darkly with one method may stain lightly with other methods.
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There are interbands in a chromosome.
There are interbands in a chromosome.
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The Q-staining methods use Giemsa dye mixture as the staining agent.
The Q-staining methods use Giemsa dye mixture as the staining agent.
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The G-staining methods produce an almost identical pattern of dark and light bands along the chromosomes.
The G-staining methods produce an almost identical pattern of dark and light bands along the chromosomes.
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The ISCN Standing Committee recommends that the chromosome nomenclature system be used only in humans.
The ISCN Standing Committee recommends that the chromosome nomenclature system be used only in humans.
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The numbers assigned to each chromosome were based on the G-banding pattern.
The numbers assigned to each chromosome were based on the G-banding pattern.
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The autosomes are numbered from 22 to 1 in decreasing order of length.
The autosomes are numbered from 22 to 1 in decreasing order of length.
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The X chromosome is a medium-sized submetacentric chromosome.
The X chromosome is a medium-sized submetacentric chromosome.
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Group A consists of large submetacentric chromosomes.
Group A consists of large submetacentric chromosomes.
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The Y chromosome has satellites on the short arm.
The Y chromosome has satellites on the short arm.
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Chromosomes in groups D and G always show satellites on the short arm.
Chromosomes in groups D and G always show satellites on the short arm.
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The group letter designations were agreed upon at the Stockholm Conference (1977).
The group letter designations were agreed upon at the Stockholm Conference (1977).
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Human chromosome nomenclature is based on the results of a single international conference.
Human chromosome nomenclature is based on the results of a single international conference.
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The chromosome bands are numbered from the ends of the chromosome arms inward.
The chromosome bands are numbered from the ends of the chromosome arms inward.
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The Paris Conference report described the original banding pattern in 1963.
The Paris Conference report described the original banding pattern in 1963.
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The term karyogram refers to a systematized array of the chromosomes prepared either by drawing, digitized imaging, or by photography.
The term karyogram refers to a systematized array of the chromosomes prepared either by drawing, digitized imaging, or by photography.
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Satellites are present on the short arms of all chromosomes in the D and G groups.
Satellites are present on the short arms of all chromosomes in the D and G groups.
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The length of each chromosome is expressed as a percentage of the total length of a diploid set.
The length of each chromosome is expressed as a percentage of the total length of a diploid set.
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The arm ratio of the chromosomes is expressed as the length of the shorter arm relative to the longer one.
The arm ratio of the chromosomes is expressed as the length of the shorter arm relative to the longer one.
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The centromeric index is expressed as the ratio of the length of the longer arm to the whole length of the chromosome.
The centromeric index is expressed as the ratio of the length of the longer arm to the whole length of the chromosome.
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The idiogram is a diagrammatic representation of a karyotype.
The idiogram is a diagrammatic representation of a karyotype.
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Study Notes
Human Chromosome Nomenclature
- Human chromosome nomenclature is based on the results of several international conferences (Denver 1960, London 1963, Chicago 1966, Paris 1971, Paris 1975, Stockholm 1977, Paris 1980, Memphis 1994, Vancouver 2004).
- The current nomenclature incorporates and supersedes all previous ISCN recommendations.
Chromosome Number and Morphology
- Autosomes are numbered from 1 to 22 in decreasing order of length.
- Sex chromosomes are referred to as X and Y.
- Chromosomes can be arranged into seven groups (A-G) based on size and centromere position.
- Group A: Large metacentric chromosomes (1-3).
- Group B: Large submetacentric chromosomes (4-5).
- Group C: Medium-sized metacentric or submetacentric chromosomes (6-12, X).
- Group D: Medium-sized acrocentric chromosomes with satellites (13-15).
- Group E: Relatively short metacentric or submetacentric chromosomes (16-18).
- Group F: Short metacentric chromosomes (19-20).
- Group G: Short acrocentric chromosomes with satellites (21-22, Y).
Non-Banding Techniques
- Parameters used to describe non-banded chromosomes:
- Length of each chromosome as a percentage of the total length of a normal haploid set.
- Arm ratio of the chromosomes.
- Centromeric index.
Banding Techniques
- A band is defined as a part of a chromosome that is clearly distinguishable from its adjacent segments by appearing darker or lighter with one or more banding techniques.
- Q-staining methods produce a fluorescent banding pattern.
- G-staining methods produce an almost identical pattern of dark and light bands.
- R-banding techniques give patterns that are opposite in staining intensity to G-staining methods.
- Two principle groups of banding techniques:
- Those resulting in bands distributed along the length of the whole chromosome (e.g. G-, Q, and R-bands).
- Those that stain specific chromosome structures and hence give rise to a restricted number of bands (e.g. C-bands, T-bands, and NORS).
Chromosome Band Nomenclature
- Each chromosome is considered to consist of a continuous series of bands, with no unbanded areas.
- Bands are allocated to various regions along the chromosome arms, and the regions are delimited by specific landmarks.
- Landmarks include the ends of the chromosome arms, the centromere, and certain bands.
- Regions are numbered from the centromere outward.
X- and Y-Chromatin
- Inactive X chromosomes and the heterochromatic segment on the long arm of the Y chromosome appear as distinctive structures in interphase nuclei.
- The terms X-chromatin (Barr body, sex chromatin, X-body) and Y-chromatin (Y-body) should be used to describe these structures.
Karyotype and Idiogram
- The term karyogram should be applied to a systematized array of the chromosomes prepared by drawing, digitized imaging, or photography.
- Karyotype is the use of nomenclature to describe the normal or abnormal, constitutional or acquired, chromosomal complement of an individual, or cell line.
- The term idiogram should be reserved for the diagrammatic representation of a karyotype.
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Description
Learn about the nomenclature of human chromosomes based on international conferences and recommendations from the ISCN Standing Committee.
