Chromosomal aberrations
Types  <ul><li>Numerical  - change in no. </li></ul><ul><li>Structural – change in structure </li></ul>
 
Monosomy <ul><li>loss of single chromosome  </li></ul><ul><li>Monosomy of autosomes is lethal </li></ul><ul><li>Turner syn...
Trisomy  <ul><li>Gain of homologous chr. </li></ul><ul><li>Trisomy 21 (down’s ) , trisomy 18 , klinefelter’s syndrome (47 ...
Nondisjunction  <ul><li>Failure of bivalents to separate during meiosis 1 , the gametes get both homologues of one chr pai...
Nondisjunction
Cause  <ul><li>Aging effect on primary oocyte </li></ul><ul><li>Radiation </li></ul><ul><li>Delayed fertilization after ov...
Polyploidy  <ul><li>Multiples of haploid no. </li></ul><ul><li>Triploidy or tetraploidy  </li></ul><ul><li>Foetus does not...
Triploidy
Structural abnormalities <ul><li>Rearrangement because of chr. Breakage & subsequent reunion in a different configuration ...
Structural abnormalities <ul><li>Translocations – reciprocal or robertsonian </li></ul><ul><li>Deletions </li></ul><ul><li...
Translocation  <ul><li>Transfer of genetic material from one chr to another </li></ul><ul><li>Reciprocal – 2 chr break & e...
Robertsonian translocation <ul><li>Breakage of 2 acrocentric chr near centromeres & fusion of long arms </li></ul><ul><li>...
 
Deletions  <ul><li>Loss of part of chr. </li></ul>•  Deletions of larger portions are usually incompatible with life •  10...
Deletions  <ul><li>Terminal – Cri – du chat syndrome ( 5p-) </li></ul><ul><li>Interstitial – 2 breaks & middle part is los...
Insertions  <ul><li>Rare nonreciprocal type of translocation  </li></ul><ul><li>A segment of chr gets inserted into anothe...
Inversion  <ul><li>2 break rearrangement  </li></ul><ul><li>Segment is reversed </li></ul><ul><li>Pericentric – when centr...
Ring chromosomes <ul><li>Break occurs in each arm & the 2 sticky ends join </li></ul><ul><li>Distal fragments are lost </l...
Philadelphia chromosome  <ul><li>Involves translocation between long arm of chr 22 & 9  </li></ul><ul><li>There is shorter...
 
Down’s syndrome <ul><li>First identified by Dr Langdon Down in 1866 </li></ul><ul><li>Trisomy 21 </li></ul><ul><li>1in 700...
Clinical findings <ul><li>Newborn – hypotonia , increased sleepiness , excess nuchal skin </li></ul><ul><li>Mental retarda...
<ul><li>Short broad hands </li></ul><ul><li>Clinodactyly ( incurving ) little finger </li></ul><ul><li>ASD,VSD , PDA </li>...
 
Edward’s syndrome <ul><li>Trisomy 18 </li></ul><ul><li>Described by Edward in 1960 </li></ul><ul><li>Rare to find live bor...
Patau’s syndrome <ul><li>Trisomy 13 </li></ul><ul><li>Die in a month </li></ul><ul><li>Growth & mental retardation </li></...
 
Turner’s syndrome <ul><li>X monosomy  , 45 X </li></ul><ul><li>described by Turner in 1938 </li></ul><ul><li>Phenotype is ...
Congenital malformations  <ul><li>Coarctation of aorta </li></ul><ul><li>VSD </li></ul><ul><li>Horseshoe kidney </li></ul>...
Klinefelter’s syndrome <ul><li>Harry klinefelter in 1942 </li></ul><ul><li>47XXY </li></ul><ul><li>Male phenotype with sex...
<ul><li>Normal intelligence </li></ul><ul><li>Testicular biopsy shows hyalinisation of seminiferous tubules </li></ul><ul>...
<ul><li>deletion (the length of which may vary) on the short arm of chromosome 5  </li></ul><ul><li>small at birth, may ha...
 
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Chromosomal Aberrations

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Chromosomal Aberrations

  1. 1. Chromosomal aberrations
  2. 2. Types <ul><li>Numerical - change in no. </li></ul><ul><li>Structural – change in structure </li></ul>
  3. 4. Monosomy <ul><li>loss of single chromosome </li></ul><ul><li>Monosomy of autosomes is lethal </li></ul><ul><li>Turner syndrome XO i.e. loss of sex chr. </li></ul><ul><li>Cause : 1. non disjunction – one gamete receives 2 copies of homologous chr. & other will have no copy </li></ul><ul><li>2. loss of chr. As it move towards pole of cell during anaphase . </li></ul>
  4. 5. Trisomy <ul><li>Gain of homologous chr. </li></ul><ul><li>Trisomy 21 (down’s ) , trisomy 18 , klinefelter’s syndrome (47 XXY) </li></ul>
  5. 6. Nondisjunction <ul><li>Failure of bivalents to separate during meiosis 1 , the gametes get both homologues of one chr pair </li></ul><ul><li>Sometimes in meiosis 2 when sister chromatids fail to separate - gets 2 copies of one of the homologues </li></ul><ul><li>It can also occur during early mitotic div. of zygote - there will be presence of 2 or more cell lines </li></ul>
  6. 7. Nondisjunction
  7. 8. Cause <ul><li>Aging effect on primary oocyte </li></ul><ul><li>Radiation </li></ul><ul><li>Delayed fertilization after ovulation </li></ul><ul><li>Effects – monosomy or trisomy </li></ul>
  8. 9. Polyploidy <ul><li>Multiples of haploid no. </li></ul><ul><li>Triploidy or tetraploidy </li></ul><ul><li>Foetus does not survive </li></ul><ul><li>Cause -1. retention of polar body </li></ul><ul><li>2. Formation of diploid sperm </li></ul><ul><li>3. Dispermy – fertilization by 2 sperms </li></ul>
  9. 10. Triploidy
  10. 11. Structural abnormalities <ul><li>Rearrangement because of chr. Breakage & subsequent reunion in a different configuration </li></ul><ul><li>Balanced – chr. Complement is complete </li></ul><ul><li>Unbalanced – when there is incorrect amount of genetic material </li></ul>
  11. 12. Structural abnormalities <ul><li>Translocations – reciprocal or robertsonian </li></ul><ul><li>Deletions </li></ul><ul><li>Insertions </li></ul><ul><li>Inversions – paracentric or pericentric </li></ul><ul><li>Ring chr. </li></ul><ul><li>Isochromosomes </li></ul>
  12. 13. Translocation <ul><li>Transfer of genetic material from one chr to another </li></ul><ul><li>Reciprocal – 2 chr break & exchange fragments </li></ul><ul><li>no. remains 46 </li></ul><ul><li>unique to a particular family </li></ul><ul><li>chr imbalance during gamete formation </li></ul>
  13. 14. Robertsonian translocation <ul><li>Breakage of 2 acrocentric chr near centromeres & fusion of long arms </li></ul><ul><li>Short arms lost – no importance they contain genes for rRNA </li></ul><ul><li>Chr no. 45 , but no loss of genetic material hence balanced </li></ul>
  14. 16. Deletions <ul><li>Loss of part of chr. </li></ul>• Deletions of larger portions are usually incompatible with life • 10-15% are due to balanced translocations in one parent 85-90% are true deletions
  15. 17. Deletions <ul><li>Terminal – Cri – du chat syndrome ( 5p-) </li></ul><ul><li>Interstitial – 2 breaks & middle part is lost eg. prader villi syndrome </li></ul><ul><li>Microdeletions </li></ul>
  16. 18. Insertions <ul><li>Rare nonreciprocal type of translocation </li></ul><ul><li>A segment of chr gets inserted into another chr </li></ul>
  17. 19. Inversion <ul><li>2 break rearrangement </li></ul><ul><li>Segment is reversed </li></ul><ul><li>Pericentric – when centromere is involved </li></ul><ul><li>Paracentric – only one arm is involved </li></ul>
  18. 20. Ring chromosomes <ul><li>Break occurs in each arm & the 2 sticky ends join </li></ul><ul><li>Distal fragments are lost </li></ul><ul><li>1/5 cases of turner’s syndrome </li></ul>
  19. 21. Philadelphia chromosome <ul><li>Involves translocation between long arm of chr 22 & 9 </li></ul><ul><li>There is shorter arm of chr 22 called philadelphia chr </li></ul><ul><li>Found in chronic myelogenous leukemia </li></ul><ul><li>Indicates better out come </li></ul>
  20. 23. Down’s syndrome <ul><li>First identified by Dr Langdon Down in 1866 </li></ul><ul><li>Trisomy 21 </li></ul><ul><li>1in 700 live births </li></ul><ul><li>Associated with increased maternal age </li></ul>
  21. 24. Clinical findings <ul><li>Newborn – hypotonia , increased sleepiness , excess nuchal skin </li></ul><ul><li>Mental retardation </li></ul><ul><li>Small stature </li></ul><ul><li>Craniofacial findings – brachycephaly ( flat occiput ) , epicanthic folds , upward slanting eyes , protruding tongue, low set ears , flat nose , low nasal bridge , high arched palate </li></ul>
  22. 25. <ul><li>Short broad hands </li></ul><ul><li>Clinodactyly ( incurving ) little finger </li></ul><ul><li>ASD,VSD , PDA </li></ul><ul><li>Anal duodenal atresia </li></ul><ul><li>Happy & affectionate </li></ul>
  23. 27. Edward’s syndrome <ul><li>Trisomy 18 </li></ul><ul><li>Described by Edward in 1960 </li></ul><ul><li>Rare to find live born </li></ul><ul><li>Do not live beyond few months </li></ul><ul><li>Features – mental retardation , failure to thrive , hypotonia , prominent occiput , low set ears , receding jaw , short sternum , clenched fists, rocker bottom feet. </li></ul>
  24. 28. Patau’s syndrome <ul><li>Trisomy 13 </li></ul><ul><li>Die in a month </li></ul><ul><li>Growth & mental retardation </li></ul><ul><li>Sloping forehead , hypertelorism , microphthalmia , cleft lip , cleft palate , polydactyly , polycystic kidneys , bicornuate uterus </li></ul>
  25. 30. Turner’s syndrome <ul><li>X monosomy , 45 X </li></ul><ul><li>described by Turner in 1938 </li></ul><ul><li>Phenotype is female </li></ul><ul><li>Short stature </li></ul><ul><li>Webbing of neck </li></ul><ul><li>Cubitus valgus </li></ul><ul><li>Low posterior hair line </li></ul><ul><li>Broad chest with widely spaced nipples </li></ul><ul><li>High arched palate </li></ul>
  26. 31. Congenital malformations <ul><li>Coarctation of aorta </li></ul><ul><li>VSD </li></ul><ul><li>Horseshoe kidney </li></ul><ul><li>Renal hypoplasia </li></ul><ul><li>Streak gonads </li></ul><ul><li>Secondary sexual characters do not develop </li></ul>
  27. 32. Klinefelter’s syndrome <ul><li>Harry klinefelter in 1942 </li></ul><ul><li>47XXY </li></ul><ul><li>Male phenotype with sex chromatin positive </li></ul><ul><li>Patients are tall thin , eunuchoid </li></ul><ul><li>Poorly developed secondary sexual characters </li></ul><ul><li>Testis are small , scrotum & penis show hypoplasia </li></ul><ul><li>Pubic ,chin & axillary hair absent </li></ul>
  28. 33. <ul><li>Normal intelligence </li></ul><ul><li>Testicular biopsy shows hyalinisation of seminiferous tubules </li></ul><ul><li>Absent spermatogenesis </li></ul><ul><li>Low serum testosterone , high FSH & LH </li></ul>
  29. 34. <ul><li>deletion (the length of which may vary) on the short arm of chromosome 5 </li></ul><ul><li>small at birth, may have respiratory problems , the larynx doesn't develop correctly, which causes the signature cat-like cry. </li></ul><ul><li>microcephaly), an unusually round face, a small chin, widely set eyes, folds of skin over their eyes, and a small bridge of the nose. </li></ul>small at birth,
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