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Chromosomal Anomalies (Lecture 2) Dr. Archana Rani Associate Professor Department of Anatomy KGMU UP, Lucknow 30.10.2014.

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Presentation on theme: "Chromosomal Anomalies (Lecture 2) Dr. Archana Rani Associate Professor Department of Anatomy KGMU UP, Lucknow 30.10.2014."— Presentation transcript:

1 Chromosomal Anomalies (Lecture 2) Dr. Archana Rani Associate Professor Department of Anatomy KGMU UP, Lucknow

2 Trisomy of Sex Chromosomes Klinefelter syndrome Triple X syndrome Double Ysyndrome

3 Klinefelter Syndrome Chromosome complement: 47,XXY Phenotype: Male Incidence: 1:1000

4 Features of Klinefelter Syndrome Tall stature; thin build; long lower limbs Testicular atrophy Female pattern of pubic hair High pitched voice Infertility (aspermatogenesis) Gynaecomastia Low level of intelligence Serum testosterone levels low to normal FSH and LH levels very high Sex chromatin positive

5 Klinefelter syndrome: Karyotype

6 Klinefelter Syndrome

7 Triple X Syndrome (Superfemale) Chromosome complement: 47,XXX Phenotype: Female Incidence: 1:1000

8 Features of Triple X Syndrome Normal in appearance Difficulty in speech, learning and emotional responses Mild mental retardation in 15-25% cases Two sex chromatin Barr bodies Infertility Wide-set eyes Amenorrhoea Expressionless face Enamel hypoplasia Deficient language skills Delayed development of motor skills

9 Superfemale: Karyotype

10 Superfemale

11 Double Y Syndrome Chromosome complement: 47,XYY Phenotype: Male Incidence: 1:1000

12 Features of Double Y Syndrome Normal in appearance Tall stature Aggressive behaviour Problems in motor and language development

13 Monosomies of Chromosomes Presence of only one member of a chromosome pair in a karyotype More detrimental than equivalent trisomy Can involve autosomes or sex chromosomes Usually abort spontaneously Monosomy of X chromosome results in XO condition called Turner syndrome

14 Turner Syndrome Chromosome complement: 45,XO Phenotype: Female Incidence: 1:

15 Features of Turner Syndrome Short statured female Sexual infantilism with primary amenorrhoea and sterility Short, webbed neck Prominent ears with defective hearing Small mandible Defective vision

16 Features of Turner Syndrome Epicanthal folds Low posterior hair line Cubitus valgus Broad chest with widely spaced nipples Cardiovascular anomalies Hyperconvex finger nails Pigmented nevi Sex chromatin negative

17 Turner Syndrome: Karyotype

18 Turner Syndrome

19 Structural Chromosomal Abnormalities Results from chromosome breakage Followed by reconstitution in an abnormal combination Breaks in any chromosome may be induced by various factors

20 Structural Chromosomal Abnormalities Deletion (Deficiency) Inversion Translocation Isochromosome Ring Chromosome

21 Deletion Loss of a (generally small) segment of chromosome A B C D E F G A B D E F G C

22 Deletion Arise through spontaneous breakage –some chromosomes have fragile spots –radiation, UV, chemicals, viruses may increase breakage

23 Deletion May arise through unequal crossing over A B C D E F G x A B C D E F F G A B C D E G Deletion Duplication

24 Deletion Large deletions will most probably be lethal Smaller deletions may allow survival –E. coli: deletions of up to 1% have been observed in living cells –D. melanogaster : deletions of up to 0.1% observed

25 Deletions in Humans Cri-du-chat syndrome –Micro deletion of chromosome 5 Di-George syndrome –Micro deletion of chromosome 22 Schizophrenia & Obsessive Compulsive Disorder –Micro deletion of chromosome 22 associated Angelman syndrome –Micro deletion of chromosome 15 Prader-Willi syndrome –Micro deletion of chromosome 15

26 Cri-du-chat syndrome 1 st autosomal deletion described Characteristic cat-like cry, which disappears with age Microcephaly Severe mental retardation Congenital heart disease Hypertelorism (widely separated eyes) Low birth weight and poor growth Severe cognitive, speech, and motor delay Behavioral problems Excessive drooling

27 Cri-du-chat syndrome

28 Prader-Willi and Angelman Syndromes Prader-Willi Syndrome Lack of muscle tone in newborn Poor swallowing reflex As adult - gross obesity Mean I.Q. ~ 50 Microdeletion of 15 Angelman Syndrome Developmentally delayed Jerky movements Stiff, fixed smile Uncontrolled laughter Abnormal E.E.G., epilepsy Microdeletion of 15

29 Inversion 180 o reversal of chromosome segment A B C D E F G H I J K A B C H G F E D I J K 180 O

30 Inversion Produced through breakage and reassociation of chromosome A B C D E F G

31 Inversion Produced through breakage and reassociation of chromosome A B C D E F G

32 Inversion May change phenotype through “position effects” –move active genes to sites generally inactive; lose gene function –move inactive genes to sites generally active; gain gene function May act to preserve blocks of genes (specific alleles) which function well together

33 Types of Inversion Paracentric Pericentric

34 Translocation Exchange of segments between non- homologous chromosomes F A B C D E L M N O P Q

35 Translocation A B C D E F O N M L Q P

36 Isochromosome Centromere of the chromosome divides transversely instead of longitudinally One arm is missing and the other arm duplicated

37 Ring Chromosome Occurs due to loss of both the ends of a chromosome The broken ends rejoin to form a ring-like chromosome Rare anomaly

38 Robertsonian Changes Fusion two chromosomes join to form one Fission one chromosome splits to form two

39 REFERENCES 1. Essentials of Anatomy for Dentistry Students,1 st Edition. 2. Langman’s Medical Embryology,11 th Edition. 3. Human Embryology, 5 th Edition.

40 MCQs 1. Klinefelter syndrome is associated with chromosome complement: a) 47,XXX b) 47,XXY c) 47,XYY d) 47,YYY

41 MCQs 2. Testicular atrophy is associated with: a) Triple X syndrome b) Double Y syndrome c) Turner syndrome d) Klinefelter syndrome

42 MCQs 3. Sex chromatin negative is a characteristic feature of: a) Triple X syndrome b) Down syndrome c) Turner syndrome d) Klinefelter syndrome

43 MCQs 4. All of the following are trisomy of sex chromosomes except: a) Turner syndrome b) Klinefelter syndrome c) Triple X syndrome d) Double Y syndrome

44 MCQs 5. Partial deletion of short arm of chromosome 5 is a feature of: a) Angelman syndrome b) Prader -Willi syndrome c) Cri-du-chat syndrome d) All of the above

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