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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

Errors in Meiosis

When Meiosis Goes Wrong

what s a mistake in meiosis
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
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 
1 non disjunction
1. NON-DISJUNCTION
  • Usually caused by the improper separation of chromosomes during either MEIOSIS I or MEIOSIS II
terms used to describe the type of non disjunction
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
terms used to describe the type of non disjunction contd
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

2 chromosomal errors
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)

what is a karyotype
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

slide14

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

slide15

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
slide16

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?