Nondisjunction and Polyploidy

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A presentation on meiosis and chromosome number that focuses on errors in meiosis.

A presentation on meiosis and chromosome number that focuses on errors in meiosis.

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  • 1. PLOIDIESMEIOSIS AND MENDELHS BIOLOGY 30.3.13
  • 2. PLOIDY AND YOU DIPLOID CELLS (2N) HAPLOID CELLS (N) Mitosis produces Meiosis produces diploid cells, which haploid cells, which in humans have 46 in humans have 23 chromosomes. chromosomes.
  • 3. The normal process of meiosis turns diploid bodycells (2n) into haploid sex cells (n), in two steps. First,homologous chromosome pairs separate in meiosis 1.Then, sister chromatids separate in meiosis 2.
  • 4. SOMETIMES, CHROMOSOMES GET STUCKDURING MEIOSIS. THIS IS CALLEDCHROMOSOMAL NONDISJUNCTION
  • 5. Nondisjunction leaves uswith messed up gametes.Instead of having 23chromosomes, they mayhave 22, 24, or evenanother number.Your body will oftenpurge these germ cellsbefore they ever get achance to fertilize. But ifthey do…
  • 6. (A FEW TOO MANY OR TOO FEW CHROMOSOMES)ANEUPLOIDY
  • 7. DOWN SYNDROME(TRISOMY 21) Total chromosomes: 47 Either the sperm or egg cell has an extra copy of chromosome 23 due to nondisjunction during meiosis. The child can be a boy or a girl. Symptoms include: short stature, weak muscles, distinct facial features, intellectual disability, heart defects, eye conditions, hearing problems, dental problems, ADHD.
  • 8. TURNER SYNDROME(MONOSOMY X) Total chromosomes: 45 Either the sperm was missing an X or Y chromosome, or the egg was missing the X chromosome and the sperm carried the Y chromosome. The baby is always female. Symptoms include: wide neck and small jaw, distinct facial features, small stature, learning disabilities, autism, lack of puberty, early menopause, infertility.
  • 9. Sometimes, meiosisgoes catastrophicallywrong, and thegametes end up with acomplete double set ofchromosomes (or acomplete missing set).This is called completenondisjunction, andthe body usuallyidentifies and purgesthese gametes.However, if a 2ngamete goes on tofertilize another normalgamete…
  • 10. (FULL SETS OF EXTRA CHROMOSOMES)POLYPLOIDY
  • 11. TRIPLOID SYNDROME Total chromosomes: 69Either the sperm or the egg has two full sets of chromosomes,leading to a triploid (3n) baby. In humans, triploid babies willeither miscarry or die within the first year of life
  • 12. SUCCESSFUL POLYPLOIDYPolyploidy in non-human species is not always fatal.Plants, especially, can survive and even thrive with extra setsof chromosomes.One reason for this is self-fertilization: plants can combinetheir own gametes, even after nondisjunction. Forexample, two messed up diploid gametes (2n) can combineto make a tetraploid (4n) plant, which will continue to havediploid gametes in the next generation.That doubles a plant species’chromosomes in one generation!
  • 13. Most plants we eat are either a result of (1) ancient, accidentallypolyploidy or (2) intentional polyploidy due to modern agriculturaltechniques. Here are some relatively dramatic examples:Diploid (2n) & Tetraploid (4n) grapes
  • 14. Monoploid (n) and triploid (3n) plant lines are usually sterile,and sometimes seedless.