Chromosomal and Genetic abnormalities


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A presentation on "Chromosomal and Genetic abnormalities ". Includes info on down syndrome , turner's syndrome,PKU and various other anomalies.

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Chromosomal and Genetic abnormalities

  1. 1. Welcome
  2. 2. Chromosomal and genetic abnormalities O A chromosome anomaly, abnormality or aberration is a missing, extra, or irregular portion of chromosomal DNA. O It can be from an atypical number of chromosomes or a structural abnormality in one or more chromosome. O Chromosome anomalies usually occur when there is an error in cell division following meiosis or mitosis..
  3. 3. Types of chromosomal anomalies There are many types of chromosome anomalies. They can be organized into two basic groups:  numerical  structural
  4. 4. Numerical disorder O This is called aneuploidy (an abnormal number of chromosomes), and occurs when an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy, tetrasomy, etc.).
  5. 5. Examples of numerical disorder
  6. 6. Symptoms of Down Syndrome O Upward slant to eyes. O Small ears that fold over at the top. O Small, flattened nose. O Small mouth, making tongue appear large. O Short neck. O Small hands with short fingers
  7. 7. O Low muscle tone. O Single deep crease across center of palm. O Looseness of joints. O Small skin folds at the inner corners of the eyes. O Excessive space between first and second toe. O In addition, down syndrome always involves some degree of mental retardation, from mild to severe. In most cases, the mental retardation is mild to moderate.
  8. 8. Trisomy-18
  9. 9. Turner’s Syndrome O An example of monosomy is Turner Syndrome, where the individual is born with only one sex chromosome, an X
  10. 10. Structural abnormalities
  11. 11. O Deletions: A portion of the chromosome is missing or deleted. Known disorders in humans include Wolf-Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4; and Jacobsen syndrome, also called the terminal 11q deletion disorder.
  12. 12. Duplications
  13. 13. O A portion of the chromosome is duplicated, resulting in extra genetic material. Known human disorders include Charcot-Marie-Tooth disease type 1A which may be caused by duplication of the gene encoding peripheral myelin protein 22 (PMP22) on chromosome 17.
  14. 14. Translocations:
  15. 15. O A portion of one chromosome is transferred to another chromosome. There are two main types of translocations: O Reciprocal translocation: Segments from two different chromosomes have been exchanged. O Robertsonian translocation: An entire chromosome has attached to another at the centromere - in humans these only occur with chromosomes 13, 14, 15, 21 and 22.
  16. 16. Inversions
  17. 17. O Inversions: A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted. O Insertions: A portion of one chromosome has been deleted from its normal place and inserted into another chromosome. O Rings: A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without loss of genetic material. O Isochromosome: Formed by the mirror image copy of a chromosome segment including the centromere.
  18. 18. O Chromosome instability syndromes are a group of disorders characterized by chromosomal instability and breakage. They often lead to an increased tendency to develop certain types of malignancies.
  19. 19. O Sickle cell disease is most commonly found in African American populations. This disease was discovered over 80 years ago, but has not been given the attention it deserves.
  20. 20. Huntington’s Disease Huntington's disease (HD) is an inherited, degenerative brain disorder which results in an eventual loss of both mental and physical control. The disease is also known as Huntington's chorea. Chorea means "dance-like movements" and refers to the uncontrolled motions often associated with the disease.
  21. 21. Phenylketonuria or PKU O People with PKU cannot consume any product that contains aspartame. O PKU is a metabolic disorder that results when the PKU gene is inherited from both parents . O Caused by a deficiency of an enzyme which is necessary for proper metabolism of an amino acid called phenylalanine.
  22. 22. O Phenylalanine is an essential amino acid and is found in nearly all foods which contain protein, dairy products, nuts, beans, tofu… etc. O A low protein diet must be followed. O Brain damage can result if the diet is not followed causing mental retardation…and mousy body odor (phenylacetic acid is in sweat).
  23. 23. Color Blindness Cause: x-linked recessive 1/10 males have, 1/100 females have Individuals are unable to distinguish shades of red-green
  24. 24. Inheritance O Most chromosome abnormalities occur as an accident in the egg or sperm, and therefore the anomaly is present in every cell of the body. Some anomalies, however, can happen after conception, resulting in Mosaicism (where some cells have the anomaly and some do not).
  25. 25. O Chromosome anomalies can be inherited from a parent or it maybe a mutation. This is why chromosome studies are often performed on parents when a child is found to have an anomaly. If the parents do not possess the abnormality it was not initially inherited; however it may be transmitted to subsequent generations.
  26. 26. How do chromosome abnormalities happen? O Chromosome abnormalities usually occur when there is an error in cell division. There are two kinds of cell division. O Mitosis results in two cells that are duplicates of the original cell. In other words, one cell with 46 chromosomes becomes two cells with 46 chromosomes each. This kind of cell division occurs throughout the body, except in the reproductive organs. This is how most of the cells that make up our body are made and replaced. O Meiosis results in cells with half the number of chromosomes, 23 instead of the normal 46. These are the eggs and sperm. O O In both processes, the correct number of chromosomes is O supposed to end up in the resulting cells. However, errors in cell division can result in cells with too few or too many copies of a chromosome. Errors can also occur when the chromosomes are being duplicated.
  27. 27. O Other factors that can increase the risk of chromosome abnormalities are: O Maternal Age: Women are born with all the eggs they will ever have. Therefore, when a woman is 30 years old, so are her eggs. Some researchers believe that errors can crop up in the eggs' genetic material as they age over time. Therefore, older women are more at risk of giving birth to babies with chromosome abnormalities than younger women. Since men produce new sperm throughout their life, paternal age does not increase risk of chromosome abnormalities.
  28. 28. O Environment: Although there is no conclusive evidence that specific environmental factors cause chromosome abnormalities, it is still a possibility that the environment may play a role in the occurrence of genetic errors.
  29. 29. Thank you