Chromosomal Variations

Dawn AdamsCytogenetics

CDC’s 2003 Science Ambassador Program

OverviewI. Chromosomal Variations

A. PolyploidyB. Aneuploidy

II. Syndromes resulting from AneuploidyA. Trisomy 13B. Trisomy 18C. Down SyndromeD. Turner SyndromeE. Klinefelter SyndromeF. XYY Syndrome

Variations in Chromosomal Number Euploidy – the usual number and sets of

chromosomes

Polyploidy – the presence of three or more complete sets of chromosomes

Aneuploidy – the presence of additional chromosomes or missing individual chromosomes

Types of Polyploidy

Triploidy – three sets of chromosomes

23 x 3 = 69

Tetraploidy – four sets of chromosomes

23 x 4 = 92

Types of Aneuploidy

Monosomy – one less chromosome(23 x 2) – 1 = 45

Trisomy – one additional chromosome

(23 x 2) + 1 = 47

Aneuploidy When aneuploidy occurs in

humans, syndromes can result. Examples include the following:

1. Trisomy 132. Trisomy 183. Down Syndrome3. Turner Syndrome4. Klinefelter Syndrome5. XYY Syndrome

Trisomy 13

Chromosomal Variation – Trisomy 13(three copies of chromosome 13)

Occurrence – 1 in 5000

Features of Trisomy 13

Severe developmental delays Head and facial abnormalities Extra fingers and toes Kidney malformations Heart defects Early death

Trisomy 18

Chromosomal Variation – Trisomy 18 (three copies of chromosome 18)

Occurrence – 1 in 5000

Features of Trisomy 18

Severe developmental delays Head and facial malformations Malformations of the hands and feet Skeletal malformations Kidney malformations Structural heart defects Early death

Down Syndrome

Chromosomal Variation – Trisomy 21 (three copies of chromosome 21)

Occurrence – 1 in 800-1000

Features of Down Syndrome

Low muscle tone Head and facial malformations Abnormalities of the extremities Developmental delays Heart malformations Increased risk of infectious disease Early death

Turner Syndrome

Monosomy of sex chromosome(only one X chromosome present)

Occurrence – 1 in 2500 live female births

Features of Turner Syndrome

Short stature Lack of ovarian development Neck abnormalities Skeletal disorders Increased risk of osteoporosis,

cardiovascular constriction, diabetes, and kidney and thyroid problems

Klinefelter Syndrome

Trisomy of sex chromosome - XXY(An additional X chromosome in males)

Occurrence – 1 in 500-1000 males

Features of Klinefelter Syndrome

Tall Sexually underdeveloped Infertility Sparse facial and body hair Developmental delays Increased risk of autoimmune

disorders, breast cancer, osteoporosis, leg ulcers, depression, and dental problems

XYY Syndrome

Trisomy of sex chromosome – XYY(An additional Y chromosome in males)

Occurrence – 1 in 1000-2000 men

Features of XYY Syndrome

Taller Comparatively low weight relative to

stature Larger craniofacial dimensions Severe acne in adolescence Behavior problems Learning disabilities Slightly lower IQ than normal

Conclusions

Variations of chromosomal number involving a set of chromosomes (polyploidy) or an individual chromosome (aneuploidy) can occur

Aneuploidy results in syndromes with distinct characteristics

References

1. Fairbanks, D. J. and W. R. Anderson. Genetics: The Continuity of Life. Pacific Grove (CA): Brooks/Cole Publishing Company; 1999.

2. National Organization for Rare Disorders. Triploid Syndrome [online]. 2004. [cited 2004 Feb 6]. Available at URL: http://www.rarediseases.org/search/rdbdetail_abstract.html? disname=Triploid%20Syndrome.

3. March of Dimes. Chromosomal Abnormalities [online]. 2004. [cited 2004 Feb 6]. Available from URL: http://www.modimes.org/professionals/681_1209.asp.

4. National Organization for Rare Disorders. Trisomy 13 [online]. 2004. [cited 2004 Feb 6]. Available at URL: http://www.rarediseases.org/ search/rdbdetail_abstract.html?disname=Trisomy%2013%20Syndrome.

References (continued)

5. National Organization for Rare Disorders. Trisomy 18 [online]. 2004. [cited 2004 Feb 6]. Available at URL: http://www.rarediseases.org/ search/rdbdetail_abstract.html?disname=Trisomy%2018%20Syndrome.

6. March of Dimes. Down Sydrome [online]. 2004. [cited 2004 Feb 6]. Available from URL: http://www.marchofdimes.com/professionals/ 681_1214.asp.

7. National Organization for Rare Disorders. Down Syndrome [online]. 2004. [cited 2004 Feb 6]. Available at URL: http://www.rarediseases.org/search/rdbdetail_abstract.html?disname=Down%20Syndrome3.

8. Turner Syndrome Society of the United States. Resources & Research: FAQs [online]. 2003. [cited 2004 Feb 6]. Available from URL: http://www.turner-syndrome-us.org/resource/faq.html.

References (continued 2)

9. National Institutes of Health. Turners Syndrome: Clinical Information [online]. 2004. [cited 2004 Feb 6]. Available from URL: http://turners.nichd.nih.gov/ClinFrintro.html.

10. American Association for Kilnefelter Syndrome Information and Support. Understanding Klinefelter Syndrome [online]. 2004. [cited 2004 Feb 6]. Available from URL: http://www.aaksis.org/bock.cfm.

11. Hambley, Vaughn. What is XXY? [online]. 2004. [cited 2002 Feb 6]. Available from URL: http://47xxy.org/XXY.htm.

12. Texas Department of Health. Birth Defect Risk Factor Series: 47, XYY [online]. 2002. [cited 2004 Feb 6]. Available from URL: http://www.tdh.state.tx.us/tbdmd/risk/risk26-XYY.htm.

References (continued 3)

13. California Center for Health Improvement. XYY Syndrome [online]. 2003. [cited 2004 Feb 6]. Available from URL: http://www.ddhealthinfo.org/ggrc/doc2.asp?ParentID=5199.