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Chromosomal Karyotypes. Dawn Adams Cytogenetics CDC’s 2003 Science Ambassador Program. Overview. I. Chromosomes A. Definition B. Structure C. Identification II. Karyotypes A. Definition B. Methods C. Staining D. Importance. Chromosomes. Definition

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Chromosomal Karyotypes

Dawn Adams

Cytogenetics

CDC’s 2003 Science Ambassador Program


Overview l.jpg
Overview

I. Chromosomes

A. Definition

B. Structure

C. Identification

II. Karyotypes

A. Definition

B. Methods

C. Staining

D. Importance


Chromosomes l.jpg
Chromosomes

Definition

  • Genetic structures of cells containing DNA

    Identification

  • Each chromosome has a characteristic length and banding pattern


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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)

Centromere


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Chromosome Labeling

Example - 1q2.4

  • The first chromosome, long arm, second region of the chromosome, the fourth band of that sub-region

Each arm divided into sub-regions and identified by a number

Each sub-region divided into bands identified with a number

Chromosome is identified with a number ranging 1-22, or X and Y


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1 2 3 4 5

6 7 8 9 10 11 12

13 14 15 16 17 18

19 20 21 22 X Y

A Karyotype

Definition

  • A photographic arrangement of a complete set of chromosomes of a cell or organism


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Obtaining a Sample

Fetal samples for karyotypes are commonly obtained in two ways

  • Amniocentesis – sample taken from the

  • fluid of the amniotic sac

  • Chorionic Villus Sampling – sample taken from the fetal tissue that forms part of the placenta


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Obtaining a Karyotype

  • Chromosomes are stained for easy visualization

  • Light microscope used to view chromosomes in metaphase of mitosis

  • Chromosomes arranged into homologous pairs based on size and banding patterns


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Staining

Banding patterns can be visually identified on chromosomes after staining.

Traditional Types

  • G-Banding – Giemsa stain

  • Q-Banding – Fluorescent stain

  • R-Banding – Reverse Giemsa stain

    New Type

  • Fluorescence In Situ Hybridization techniques


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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.


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References

  • 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: http://www.nlm.nih.gov/medlineplus/ency/article/003921.htm.

  • NIH. Chorionic villus sampling [online]. 2004. [cited 2004 Feb 6]. Available from URL: http://www.nlm.nih.gov/ medlineplus/ency/article/003406.htm.

  • Campbell, N. A. Biology. 3rd ed. Redwood City, CA: The Benjamin/Cummings Publishing Company, Inc.; 1993.


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References (continued)

  • On-line medical dictionary. G-banding: Banding pattern. 1997. [cited 2004 Feb 6]. Available from URL: http://cancerweb.ncl.ac.uk/cgi-bin/omd?G-banding.

  • On-line medical dictionary. Q-banding. 2000. [cited 2004 Feb 6]. Available from URL: http://cancerweb.ncl.ac.uk/cgi-bin/omd?query=q-banding.

  • On-line medical dictionary. R-banding stain. 2000. [cited 2004 Feb 6]. Available from URL: http://cancerweb.ncl.ac.uk/cgi-bin/omd?R-banding+stain.

  • National Human Genome Research Institute, Fluorescence In Situ Hybridization (FISH). 2004 [cited 2004 Feb 6]. Available from URL: http://www.genome.gov/10000206.