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Chromosomal Variations. This presentation will look at alterations in chromosome number and specific syndromes that arise in humans from these variations. Overview. I. Chromosomal Variations A. Polyploidy B. Aneuploidy II. Syndromes resulting from Aneuploidy A. Trisomy 13

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Chromosomal Variations


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    1. Chromosomal Variations This presentation will look at alterations in chromosome number and specific syndromes that arise in humans from these variations.

    2. Overview I. Chromosomal Variations A. Polyploidy B. Aneuploidy II. Syndromes resulting from Aneuploidy A. Trisomy 13 B. Trisomy 18 C. Down Syndrome D. Turner Syndrome E. Klinefelter Syndrome F. XYY Syndrome

    3. Variations in Chromosomal Number • Euploidy – the normal number and sets of chromosomes • Polyploidy – the presence of three or more complete sets of chromosomes • Aneuploidy – the presence of additional or missing individual chromosomes

    4. Types of Polyploidy • Triploidy – three sets of chromosomes 23 x 3 = 69 • Tetraploidy – four sets of chromosomes 23 x 4 = 92

    5. Types of Aneuploidy • Monosomy – one less chromosome (23 x 2) – 1 = 45 • Trisomy – one additional chromosome (23 x 2) + 1 = 47

    6. Aneuploidy in Humans • When aneuploidy occurs in humans, syndromes can result. Examples include the following: 1. Trisomy 13 2. Trisomy 18 3. Down Syndrome 3. Turner Syndrome 4. Klinefelter Syndrome 5. XYY Syndrome

    7. Trisomy 13 • Chromosomal Variation – Trisomy 13 (three copies of chromosome 13) • Occurrence – 1 in 5000

    8. Features of Trisomy 13 • Severe mental retardation • Head and facial abnormalities • Extra fingers and toes • Kidney malformations • Heart defects • Early death

    9. Trisomy 18 • Chromosomal Variation – Trisomy 18 (three copies of chromosome 18) • Occurrence – 1 in 5000

    10. Features of Trisomy 18 • Severe mental retardation • Head and facial malformations • Malformations of the hands and feet • Skeletal malformations • Kidney malformations • Structural heart defects • Early death

    11. Down Syndrome • Chromosomal Variation – Trisomy 21 (three copies of chromosome 21) • Occurrence – 1 in 800-1000

    12. Features of Down Syndrome • Low muscle tone • Head and facial malformations • Abnormalities of the extremities • Mental retardation • Heart malformations • Increased risk of infectious disease • Early death

    13. Turner Syndrome • Monosomy of sex chromosome (only one X chromosome present) • Occurrence – 1 in 2500 live female births

    14. 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

    15. Klinefelter Syndrome • Trisomy of sex chromosome - XXY (An additional X chromosome in males) • Occurrence – 1 in 500-1000 males

    16. 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

    17. XYY Syndrome • Trisomy of sex chromosome – XYY (An additional Y chromosome in males) • Occurrence – 1 in 1000-2000 men

    18. 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

    19. 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

    20. References 1. Fairbanks, D. J. and W. R. Anderson. Genetics: The Continuity of Life. Brooks/Cole Publishing Company, Pacific Grove, CA, 1999. 2. http://www.rarediseases.org/ (search triploidy, trisomy 13, trisomy 18, Down syndrome, accessed Feb. 6, 2004) 3. http://www.modimes.org/ professionals/681_1209.asp and … /681_1214.asp 4. http://www.turner-syndrome-us.org/ 5. http://turners.nichd.nih.gov/ClinFrintro.html 6. http://www.aaksis.org/ 7. http://47xxy.org/XXY.htm 8. http://www.tdh.state.tx.us/tbdmd/risk/risk26-XYY.htm 9. http://www.ddhealthinfo.org/ggrc/doc2.asp?ParentID=5199