Chromosomal Abberations PDF

Chromosomal abberations  Definition Deviation from normal NO. Or str of chr Commonly Cause MR & developmental R  strucural aberrations= mutation Inf Viral irradiation Balanced ab = Insecticides chr has normal Drugs genetic information...

Chromosomal abberations  Definition Deviation from normal NO. Or str of chr Commonly Cause MR & developmental R  strucural aberrations= mutation Inf Viral irradiation Balanced ab = Insecticides chr has normal Drugs genetic information unbalanced ab = chr miss genetic information strucural abberations types 1- Break Heal by reunion of sticky ends  strucural abberations types 2- Deletion = Loss of fragmented part terminal interstitial ring 1 br+ loss 2 br+ from 1 end loss of sgment in between: 2 br+ loss+ reunion in a ring Wolf s= deletion of short arm of chr 4 Cri du chat s= deletion of short arm of chr 5  strucural abberations types 3-Duplication Addition of extra piece of homologous chr due to unequal crossing over → 2 copies of same gene on chr  strucural abberations types 4- Inversion 2 breaks + reunion in inverted form:- Peri centric: break on both sides of centromere Para centric: break on one side  strucural abberations types 5- Transfere of chr segment Translocation to non homologous chr t 14 21 a) Robersonian TL= Centric fusion: In acrocentric chr 14&21 Fusion of both long arms→ chr t Loss both short arms( insignificant) 3-4% of cases of Down s.  N.B IF a parent is a carrier of chr 21 translocation The risk of having Down child is up to 100% b) Reciprocal translocation: Transfere of chr segment to non homologous chr Its balanced as no genes are lost or added If chr 22&9 = philadelphia chr Diagnostic of CML  strucural abberations types 6-Isochromosomes TS division of chr during anaphase of mitosis 2 non similar chromatids 2 non similar chromsomes 1 has 2 long arms & 1 has 2 short arms In submetacentric chr