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Chromosomal Aberration


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It includes the overview about chromosomes and different chromosomal aberrations.

Published in: Education
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Chromosomal Aberration

  2. 2. Cytogenetics o Karyotype – microscopic examination of chromosome Main feature to identify and classify chromosomes 1. Size 2. Location of the centromere 3. Banding patterns
  3. 3. G-Banded Metaphase Chromosome
  4. 4. Chromosomal Aberration o is substantial changes in chromosome structure o typically affect multiple genes (loci) o due to error in cell division (non-disjunction of chromosomes and chromatids), maternal age or environment
  5. 5. Relationship Between Age and Aneuploidy  Older mothers more likely to produce aneuploid eggs  Trisomy 21  Due to meiotic non-disjunction in during oocyte maturation
  6. 6. Meiotic Nondisjunction Generates Aneuploidies abnormal gametes Zygotic Ploidy Zygotic Ploidy
  7. 7. Types of Chromosomal Abnormalities o aneuploidy o polyploidy Numerical Abnormalities Structural Abnormalities o deletion o duplication o inversion o translocation
  8. 8. Numerical Abnormalities o Aneuploidy o Variation in the number of particular chromosomes within a set 1. Hyperploidy- gain of chromosome/s • Trisomy- 2n + 1 • Double trisomy- 2n + 1 +1 • Tetrasomy- 2n + 2 2. Hypoploidy- loss of chromosome/s • Monosomy- 2n –1 • Double monosomy- 2n –1-1 • Nullisomy- 2n-2 o Polyploidy o Condition in which the cells have more than 2 homologous sets of chromosome 1. triploid (3n) 2. tetraploid (4n) 3. Pentaploid (5n)
  9. 9. o Aneuploidy of sex chromosome o Occurs in 1 in 500-1000 o Sterile o No obvious facial dysmorphy o Narrower shoulders and wider hips Klinefelter Syndrome – 47, XXY
  10. 10. o Smaller testes and penis o Decreased sexual interest o Weaker bones o Lower energy o Breast growth o Less facial and body hair o Reduced muscle tone Klinefelter Syndrome – 47, XXY
  11. 11. o Aneuploidy of sex chromosome o Aggressive due to high level of testosterone (prone to violent wife beating) o Adult male could be more impulsive and emotionally immature Jacob Syndrome – 47, XYY “How to tell if your child is a SERIAL KILLER?”
  12. 12. o occurs in 1 in 1000 o lanky, clumsy, uncoordinated o dyslexia – develop in reading disorder o problem in motor coordination o behavioral problems o behavioral tantrums o more impulsive o emotionally immature Jacob Syndrome – 47, XYY
  13. 13. Turner Syndrome – 47, X o Aneuploidy of the sex chromosome o demonstrate visuospatial deficits including poor handwriting and likely underdeveloped arithmetic skills
  14. 14. Turner Syndrome – Monosomy 47, X o Short stature o Ovarian failure o otitis media o early OM in TS could lead in dyslexia (reading disorder)
  15. 15. Patau’s Syndrome - Trisomy 13 o Severe intellectual disability o Physical abnormalities in in many parts of the body o Heart defects, brain and spinal cord abnormalities
  16. 16. Patau’s Syndrome - Trisomy 13 o Very small or poorly developed eyes (micropthalmia) o Extra fingers or toes o Weak muscle tone (hypotonia)
  17. 17. Edward’s Syndrome – Trisomy 18 o intestines protruding outside the body o intellectual disabilities o delayed development o feeding and breathing difficulties
  18. 18. Edward’s Syndrome – Trisomy 18 o Arthrogryposis - a muscle disorder that causes multiple joint contractures at birth
  19. 19. Down Syndrome - Trisomy 21 o physical growth delays o severe degree of intellectual disability o short stature o delayed mental and social development o Impulsive behavior o Poor judgment o Short attention span o Slow learning
  20. 20. Down Syndrome - Trisomy 21 o Sleep apnea - sleep disorder characterized by pauses in breathing or instances of shallow or infrequent breathing during sleep o Dementia - decline in mental ability severe enough to interfere with daily life, memory loss o Hypothyroidism - under active thyroid
  21. 21. Aneuploid Condition in Humans Condition Frequency Syndrome Characteristics Autosomal Trisomy 21 1/800 Down Mental retardation, abnormal pattern of palm creases,slanted eyes, flattened face, short stature Trisomy 18 1/6,000 Edward Mental and physical retardation, facial abnormalities, extreme muscle tone, early death Trisomy 13 1/15,000 Patau Mental and physical retardation, wide variety of defects in organs, large triangular nose, early death Sex Chromosome XXY 1/1,000 (males) Klinefelter Sexual immaturity (no sperm), breast swelling XYY 1/1,000 (males) Jacob Tall XXX 1/1,500 (females) Metafemale Tall and thin, menstrual irregularity X0 1/1,500 (females) turner Short stature, webbed neck, sexualy undeveloped
  22. 22. Effects of Nullisomics • dwarf • less tillering • female fertile • male sterile • awnless Nullisomics-Mutants of the Ear in Wheat (Triticum aestivum) Ear shape of the wild type (WT) and of several mutants lacking single pairs of chromosomes (nullisomics). Due to the hexaploidy, the lack of a pair of chromosomes is tolerated. The effects are usually different though stunted growth is usually one of them.
  23. 23. Polyploidy - with more than 2 sets of genome o most common in plants which are asexually propagated and infrequent in animals o for sexually reproducing organisms, sex chromosome balance must be maintained Detection: • change in morphology • change in fertility • change in interspecific cross ability
  24. 24. Triploid Plants (3n) Tetraploid Plants (4n)
  25. 25. Benefit of Odd Ploidy-Induced Sterility  Seedless fruit  watermelons and bananas  asexually propagated by human via cuttings  Seedless flowers  Marigold flowering plants  Prevention of cross pollination of transgenic plants
  26. 26. Structural Abnormalities Deletion Duplication Inversion Translocation Amount of genetic information in the chromosome can change. The genetic material remains the same but it is rearrange.
  27. 27. Deletion o Loss of a region of chromosome o A chromosomal deficiency occurs when a chromosome breaks and a fragment is lost
  28. 28.  Phenotypic consequences of deficiency depends on  Size of the deletion  Functions of the genes deleted  Phenotypic effect of deletions usually detrimental Deficiencies Interstitial Terminal Two types of deletion
  29. 29. Cri-du-chat Syndrome o High-pitched cry o intellectual disability o delayed development o small head size o low birth weight o weak muscle tone in infant
  30. 30. DiGeorge Syndrome o deletion in long arm of chromosome #22 o congenital heart disease o Cyanosis o learning difficulties o psychiatric disorders
  31. 31. Angelman Syndrome o deletion in chromosome #15 o uncontrolled laughter o no speech development
  32. 32. Duplication o A chromosomal duplication is usually caused by abnormal events during recombination
  33. 33. Duplication o Small duplications often are not accompanied by a phenotypic effect o Large duplications produce phenotypes through imbalanced gene dosage o tend to be less detrimental o constitute a major force of genome evolution. Direct Inverted
  34. 34. Inversion o A segment of chromosome that is flipped relative to that in the homologue o Two breaks in one chromosome o The fragment generated rotates 180o and reinserts into the chromosome Pericentric - involves p and q arm Paracentric - involves only one arm
  35. 35. Inversion o arise from chromosome entanglements and breakages during meiotic prophase; also from recombination between transposable elements o Cause linear rearrangement of genes in a chromosome o In inversion heterozygotes , a loop forms from the pairing of the inverted and non-inverted regions
  36. 36. Translocation o When a segment of one chromosome becomes attached to another o In reciprocal translocations two non-homologous chromosomes exchange genetic material o Usually generate so-called balanced translocations o Usually without phenotypic consequences o Although can result in position effect
  37. 37. Reciprocal Translocation • Involves two chromosomes • One break in each chromosome • The two chromosomes exchange broken segments
  38. 38. Robertsonian Translocation • Named after W. R. B. Robertson who first identified them in grasshoppers in 1916 • Most common structural chromosome abnormality in humans – Frequency = 1/1000 livebirths • Involves two acrocentric chromosomes • Two types – Homologous acrocentrics involved – Non-Homologous acrocentrics involved + = lost + = lost
  39. 39. Robertsonian Translocation  This translocation occurs as such  Breaks occur at the extreme ends of the short arms of two non- homologous acrocentric chromosomes  The small acentric fragments are lost  The larger fragments fuse at their centromeic regions to form a single chromosome  This type of translocation is the most common type of chromosomal rearrangement in humans
  40. 40. Isochromosome & Ring Chromosome o Mirror image chromosome o Loss of one arm with duplication of other Loss of p-arm Duplication of q-arm o Breaks occur in both arms of a chromosome. o The two broken ends anneal; the two acentric fragments are lost. o Results in double deletion (in p and in q). o Epilepsy, mental retardation and craniofacial abnormalities
  41. 41. Induction of Chromosomal Aberrations by Carbamate Fungicide in Fish Clarius batrachus (Asian Catfish) Ajay Singh and Pallavi Srivastava November 2013 ISSN 2276-7118
  42. 42. Abstract Chromosomal studies have received considerable attention, in part from a growing interest in the evaluation of genotoxicity of environmental toxicants and carcinogenns. In view of fast growing agricultural applications of chemicals, fertilizers and pesticides, the evaluation of their genotoxic potential is necessity to conduct adequate hazard and to produce safer and sustainable aquatic environment. In this paper genotoxity of fungicide, Mancozeb concluded that acute exposure of fungicide induced cytogentic effects, as the incidence of chromosome aberrations (CA) was positively correlated with duration of exposure. Fishes of control group was maintaned without any treatment, positive control group was treated with mitomycin-C and two experimental groups were exposed to sub-lethal doses of Mancozeb (11.43mg/l and 22.87 mg/l). After 24h, 48h, 72h, or 96h of exposure the mitotic index was significantly (p<0.05) decreased in kidney tissue of fish. These findings thus indicate that Mancozeb is able to induce genotoxic effect in catfish.
  43. 43. Thank You! 