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Chromosomal Variations

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Chromosomal Variations
Dawn AdamsCytogeneticsCDC’s 2003 Science Ambassador Program
Overview
I. Chromosomal VariationsA. PolyploidyB. AneuploidyII. 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 chromosomesPolyploidy – the presence of three or more complete sets of chromosomesAneuploidy – the presence of additional chromosomes or missing individual chromosomes
Types of Polyploidy
Triploidy – three sets of chromosomes23 x 3 = 69Tetraploidy – four sets of chromosomes23 x 4 = 92
Types of Aneuploidy
Monosomy – one less chromosome(23 x 2) – 1 = 45Trisomy – 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 delaysHead and facial abnormalitiesExtra fingers and toesKidney malformationsHeart defectsEarly death
Trisomy 18
Chromosomal Variation – Trisomy 18 (three copies of chromosome 18)Occurrence – 1 in 5000
Features of Trisomy 18
Severe developmental delaysHead and facial malformationsMalformations of the hands and feetSkeletal malformationsKidney malformationsStructural heart defectsEarly death
Down Syndrome
Chromosomal Variation – Trisomy 21 (three copies of chromosome 21)Occurrence – 1 in 800-1000
Features of Down Syndrome
Low muscle toneHead and facial malformationsAbnormalities of the extremitiesDevelopmental delaysHeart malformationsIncreased risk of infectious diseaseEarly death
Turner Syndrome
Monosomy of sex chromosome(only one X chromosome present)Occurrence – 1 in 2500 live female births
Features of Turner Syndrome
Short statureLack of ovarian developmentNeck abnormalitiesSkeletal disordersIncreased 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
TallSexually underdevelopedInfertilitySparse facial and body hairDevelopmental delaysIncreased 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
TallerComparatively low weight relative to statureLarger craniofacial dimensionsSevere acne in adolescenceBehavior problemsLearning disabilitiesSlightly lower IQ than normal
Conclusions
Variations of chromosomal number involving a set of chromosomes (polyploidy) or an individual chromosome (aneuploidy) can occurAneuploidy results in syndromes with distinct characteristics
References
Fairbanks, D. J. and W. R. Anderson. Genetics: The Continuity of Life. Pacific Grove (CA): Brooks/Cole Publishing Company; 1999.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.March of Dimes. Chromosomal Abnormalities [online]. 2004. [cited 2004 Feb 6]. Available from URL:http://www.modimes.org/professionals/681_1209.asp.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)
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.March of Dimes. Down Sydrome [online]. 2004. [cited 2004 Feb 6]. Available from URL:http://www.marchofdimes.com/professionals/ 681_1214.asp.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.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)
National Institutes of Health. Turners Syndrome: Clinical Information [online]. 2004. [cited 2004 Feb 6]. Available from URL:http://turners.nichd.nih.gov/ClinFrintro.html.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.Hambley, Vaughn. What is XXY? [online]. 2004. [cited 2002 Feb 6]. Available from URL:http://47xxy.org/XXY.htm.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)
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.

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Chromosomal Variations