Chromosomal Karyotypes Dawn Adams Cytogenetics CDCs 2003 Science

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 n Genetic structures of cells containing DNA Identification n Each chromosome has a characteristic length and banding pattern

The breakdown of a Chromosome n Each autosome is numbered from 1 -22, sex chromosomes either X or Y p arm (short arm) Centromere q arm (long arm)

Chromosome Labeling 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 subregion divided into bands identified with a number Example - 1 q 2. 4 n The first chromosome, long arm, second region of the chromosome, the fourth band of that sub-region

A Karyotype Definition n A photographic arrangement of a complete set of chromosomes of a cell or organism 1 6 13 19 2 7 3 8 14 9 15 20 4 10 5 11 16 21 17 22 12 18 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 sac 2. Chorionic Villus Sampling – sample taken from the fetal tissue that forms part of the placenta

Obtaining a Karyotype n n n 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 n G-Banding – Giemsa stain n Q-Banding – Fluorescent stain n R-Banding – Reverse Giemsa stain New Type n Fluorescence In Situ Hybridization techniques

Importance of Karyotypes show the chromosomal makeup of an individual. Knowing the number of chromosomes is essential for identifying chromosomal variations that cause genetic disorders.

References 1. 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/00392 1. 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. 3 rd 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=qbanding. 7. On-line medical dictionary. R-banding stain. 2000. [cited 2004 Feb 6]. Available from URL: http: //cancerweb. ncl. ac. uk/cgi-bin/omd? Rbanding+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.