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Errors in Meiosis

Errors in Meiosis. When Meiosis Goes Wrong. What’s a Mistake in Meiosis? . Too many or not enough chromosomes which can lead to genetic disorders Chromosomes may have errors that can lead to new traits being expressed. Mutations.

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Errors in Meiosis

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  1. Errors in Meiosis When Meiosis Goes Wrong

  2. What’s a Mistake in Meiosis? • Too many or not enough chromosomes which can lead to genetic disorders • Chromosomes may have errors that can lead to new traits being expressed

  3. Mutations • When DNA is damaged or changed so that the code carried by that gene is no longer the same NOTE!!! • Not all mutations can become expressed (so not all changes can be seen in the organism) • Not all mutations are bad 

  4. Types of Errors

  5. 1. NON-DISJUNCTION • Usually caused by the improper separation of chromosomes during either MEIOSIS I or MEIOSIS II

  6. Terms Used to Describe the type of Non-Disjunction • Aneuploidy – Means too few or too many chromosomes. • Monosomy - Having only 1 copy of a particular chromosome. • Example: Turner syndrome – missing X chromosome or possess an abnormal X chromosome • Polysomy – Having one or more extra sets of chromosomes. • Example: Down Syndrome – extra chromosome #21

  7. Terms Used to Describe the type of Non-Disjunction (contd.) • Polyploidy – Having 3, 4 or more sets of chromosomes instead of the 2 present in diploids  Occurs very frequently in plants

  8. 2. CHROMOSOMAL ERRORS • Deletions:  Sections of DNA are missing • Duplications:  Sections of DNA are duplicated • Inversions: Sections of DNA are attached in reverse order • Translocations:  Sections of DNA are reattached to the wrong chromosome (non-homologous)

  9. Errors are detected by analyzing the karyotype

  10. What is a Karyotype? • A karyotype is a photographic inventory of an individual’s chromosomes • Best photographed during Metaphase A karyotype usually shows 22 pairs of autosomes(non-sex chromosomes) and one pair of sex chromosomes

  11. http://www.bioteach.ubc.ca/Bio-industry/Xenon/graphics/karyotype.gifhttp://www.bioteach.ubc.ca/Bio-industry/Xenon/graphics/karyotype.gif

  12. It is possible to have trisomy of chromosomes 13, 15, 18, 21 & 22 • Unfortunately it is usually fatal if the embryo has trisomy of any of the other autosomal chromosomes

  13. With a partner, examine the karyotype on the next slide • Tell me: what type of chromosomal disorder are you looking at? (nondisjunction or mistake in chromosome structure) • How do you know?

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