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Chromosomal Karyotypes
Dawn AdamsCytogeneticsCDC’s 2003 Science Ambassador Program
Chromosomal Karyotypes
I. ChromosomesA. DefinitionB. StructureC. IdentificationII. KaryotypesA. DefinitionB. MethodsC. StainingD. Importance
DefinitionGenetic structures of cells containing DNAIdentificationEach chromosome has a characteristic length and banding pattern
The breakdown of a Chromosome
Each autosome is numbered from 1-22, sex chromosomes either X or Y
p arm(short arm)
q arm(long arm)
Chromosome Labeling
Example - 1q2.4The first chromosome, long arm, second region of the chromosome, the fourth band of that sub-region
Chromosome is identified with a number ranging 1-22, or X and Y
Each arm divided into sub-regions and identified by a number
Each sub-region divided into bands identified with a number
A Karyotype
DefinitionA photographic arrangement of a complete set of chromosomes of a cell or organism
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18
19 20 21 22 X Y
Obtaining a Sample
Fetal samples for karyotypes are commonly obtained in two ways
Amniocentesis – sample taken from thefluid of the amniotic sacChorionic Villus Sampling – sample taken from the fetal tissue that forms part of the placenta
Obtaining a Karyotype
Chromosomes are stained for easy visualizationLight microscope used to view chromosomes in metaphase of mitosisChromosomes arranged into homologous pairs based on size and banding patterns
Banding patterns can be visually identified on chromosomes after staining.Traditional TypesG-Banding – Giemsa stainQ-Banding – Fluorescent stainR-Banding – Reverse Giemsa stainNew TypeFluorescence In Situ Hybridization techniques
Importance of Karyotypes
Karyotypes show the chromosomal makeup of an individual. Knowing the number of chromosomes is essential for identifying chromosomal variations that cause genetic disorders.
Fairbanks, D. J., Anderson, W. R. Genetics: The Continuity of Life.Pacific Grove, CA: Brooks/Cole Publishing Company; 1999.NIH. Amniocentesis [online]. 2004. [cited 2004 Feb 6]. Available from URL: Chorionic villus sampling [online]. 2004. [cited 2004 Feb 6]. Available from URL: medlineplus/ency/article/003406.htm.Campbell, N. A. Biology. 3rded. Redwood City, CA: The Benjamin/Cummings Publishing Company, Inc.; 1993.
References (continued)
On-line medical dictionary. G-banding: Banding pattern. 1997. [cited 2004 Feb 6]. Available from URL: medical dictionary. Q-banding. 2000. [cited 2004 Feb 6]. Available from URL: medical dictionary. R-banding stain. 2000. [cited 2004 Feb 6]. Available from URL: Human Genome Research Institute, Fluorescence In Situ Hybridization (FISH). 2004 [cited 2004 Feb 6]. Available from URL:





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