Chromosomal Karyotypes

Dawn Adams

Cytogenetics

CDC’s 2003 Science Ambassador Program

Overview

I. Chromosomes A. Definition B. Structure

C. IdentificationII. Karyotypes

A. Definition B. Methods C. Staining D. Importance

Chromosomes

Definition Genetic structures of cells

containing DNA

Identification Each 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 Yp arm (short

arm)

q arm (long arm)

Centromere

Chromosome Labeling

Example - 1q2.4 The 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

Definition A

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

1.Amniocentesis – sample taken from the

fluid of the amniotic sac2.Chorionic Villus Sampling – sample

taken from the fetal tissue that forms part of the placenta

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

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

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.

References1. Fairbanks, D. J., Anderson, W. R. Genetics: The

Continuity of Life. Pacific Grove, CA: Brooks/Cole Publishing Company; 1999.

2. NIH. Amniocentesis [online]. 2004. [cited 2004 Feb 6]. Available from URL: http://www.nlm.nih.gov/medlineplus/ency/article/003921.htm.

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

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

References (continued)5. 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.

6. 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.

7. 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.

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