Chromosomal abnormalities


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Chromosomal abnormalities

  1. 1. Chromosomal Abnormalities
  2. 2. What are chromosomes? <ul><li>Humans have 23 pairs of chromosomes, with one chromosome from each parent. The chromosomes are coiled up DNA. Under normal conditions all of the chromosomes are inherited intact. </li></ul>This is a normal karyotype of human chromosomes. A karyotype is a picture of chromosomes lined up to look at and compare.
  3. 3. Chromosomal abnormalities <ul><li>Incorrect number of chromosomes </li></ul><ul><ul><li>nondisjunction </li></ul></ul><ul><ul><ul><li>chromosomes don’t separate properly during meiosis </li></ul></ul></ul><ul><ul><li>breakage of chromosomes </li></ul></ul><ul><ul><ul><li>deletion </li></ul></ul></ul><ul><ul><ul><li>duplication </li></ul></ul></ul><ul><ul><ul><li>inversion </li></ul></ul></ul><ul><ul><ul><li>translocation </li></ul></ul></ul>
  4. 4. Chromosomal Disorders <ul><li>Chromosomal deletion : when cells go through meiosis, portions of the chromosome are lost. </li></ul><ul><li>Chromosomal inversion : when cells go through meiosis, parts of the chromosome are flipped. </li></ul><ul><li>Chromosomal translocation : when cells go through meiosis, parts of the chromosomes stick together and switch. </li></ul><ul><li>Chromosomal non-disjunction : when cells go through meiosis the chromosomes don’t separate correctly and either too many or not enough are passed on. </li></ul>
  5. 5. Single Chromosome Disorders <ul><li>Deletion </li></ul><ul><li>Genetic material is missing </li></ul><ul><li>2. Duplication </li></ul><ul><li>Genetic material is present twice </li></ul><ul><li>3. Inversion </li></ul><ul><li>Genetic material is “flipped” </li></ul>
  6. 6. Two Chromosome Disorders ( Both types are called “translocation”) <ul><li>Insertion </li></ul><ul><li>Genetic material is added from another chromosome </li></ul><ul><li>Translocation </li></ul><ul><li>Material is swapped with another chromosome </li></ul>
  7. 7. Nondisjunction <ul><li>Problems with meiotic spindle (doesn’t attach or pull correctly) cause errors in daughter cells </li></ul><ul><ul><li>chromosomes do not separate properly during Meiosis 1 </li></ul></ul><ul><ul><li>sister chromatids fail to separate during Meiosis 2 </li></ul></ul><ul><ul><li>too many or too few chromosomes </li></ul></ul>2n n n n-1 n+1
  8. 8. Alteration of chromosome number
  9. 9. Nondisjunction <ul><li>Baby has wrong chromosome number </li></ul><ul><ul><li>trisomy </li></ul></ul><ul><ul><ul><li>cells have 3 copies of a chromosome </li></ul></ul></ul><ul><ul><li>monosomy </li></ul></ul><ul><ul><ul><li>cells have only 1 copy of a chromosome </li></ul></ul></ul>trisomy 2n+1 monosomy 2n-1
  10. 10. Human chromosome disorders <ul><li>High frequency in humans </li></ul><ul><ul><li>most embryos are spontaneously aborted </li></ul></ul><ul><ul><li>alterations are too disastrous </li></ul></ul><ul><ul><li>developmental problems result from biochemical imbalance </li></ul></ul><ul><li>Certain conditions are tolerated </li></ul><ul><ul><li>upsets the balance less, so child survives </li></ul></ul><ul><ul><li>characteristic set of symptoms is called a syndrome </li></ul></ul>
  11. 11. Down syndrome <ul><li>Trisomy 21 </li></ul><ul><ul><li>3 copies of chromosome 21 </li></ul></ul><ul><ul><li>1 in 700 children born in U.S. </li></ul></ul><ul><li>Chromosome 21 is the smallest human chromosome </li></ul><ul><ul><li>but still severe effects </li></ul></ul><ul><li>Frequency of Down syndrome correlates with the age of the mother </li></ul>
  12. 12. Trisomy 21
  13. 13. Sex chromosomes in different numbers <ul><li>Human development more tolerant of wrong numbers in sex chromosome </li></ul><ul><li>But produces a variety of distinct conditions in humans </li></ul><ul><ul><li>XXY = Klinefelter’s syndrome male </li></ul></ul><ul><ul><li>XXX = Trisomy X female </li></ul></ul><ul><ul><li>XYY = Jacob’s syndrome male </li></ul></ul><ul><ul><li>XO = Turner syndrome female </li></ul></ul>