1. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Conditions caused by anomalies in chromosome number This PowerPoint file contains a number of slides that may be useful for teaching of genetics concepts. You may use these slides and their contents for non-commercial educational purposes.

2. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Fig. 2.2 ©Scion Publishing Ltd A child with Down syndrome

3. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Fig. 2.3 ©Scion Publishing Ltd Photo. (c) courtesy of Dr Godfrey Wilson Turner syndrome (a) Puffy feet. (b) redundant skin at back of neck. (c) Histology of gonads: ovarian cortical strome devoid of germ cell elements.

4. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk 47,XX,+?mar

5. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Three different patterns of chromosomes can cause Down syndrome 1% have mosaicism with normal and trisomy 21 cell lines (and usually have much milder features because of the presence of the normal cells); occurs postzygotically Non-disjunction 95% people have three separate copies of chromosome 21 - trisomy 21 4% have the extra copy of chromosome 21 because of a Robertsonian translocation

6. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Two other important autosomal trisomies Edwards syndrome (trisomy 18) –1 in 3000 births –multiple malformations (especially heart, kidneys) –clenched hands with overlapping fingers Patau syndrome (trisomy 13) –1 in 5000 births –multiple malformations –affects midline structures particularly: incomplete lobation of brain; cleft lip; congenital heart disease Both syndromes have a very poor prognosis: majority of babies dying in first few weeks of life. If a baby survives (very unusual) there is severe mental retardation.

7. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Two important conditions caused by anomalies of sex chromosome number Klinefelter syndrome –47,XXY –1 in 1000 males –Infertility (atrophic testes do not produce sperm) –Poorly developed 2ndy sexual characteristics in some (lack of testosterone) –Tall Turner syndrome –45,X –1 in 5000 females –99% are lost spontaneously in pregnancy –Short stature –Primary amenorrhoea (ovaries involute before birth) –Congenital heart disease (coarctation of aorta) 20%

8. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Numerical chromosome abnormalities Gain or loss of complete chromosomes Common cause is non-disjunction (Usually in germ cells at meiosis. Occasionally in somatic cells resulting in mosaicism.) Serious, often lethal consequences (particularly autosomal anomalies) Autosomal monosomies catastrophic Fewer serious effects from sex chromosome anomalies

9. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Trisomies appear to be associated with an increase in maternal age –eggs held at crossing-over stage in meiosis from approx 6 months gestation –so wear and tear with increasing maternal age in machinery for cell division thought to be a major component (plus some other factors) The trisomy 21 type of Down syndrome is the result of an error in meiosis, and has a recurrence risk of about 1 in 100.