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Topic 4.2 & 10.1 Notes. Meiosis. A reduction in chromosomes to form HAPLOID cells. 2N to 1N. Homologous pairs . They associate with each other during prophase 1 through synapsis. Chromosomes replicate in which phase?. S phase!. Prophase 1.

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meiosis
Meiosis
  • A reduction in chromosomes to form HAPLOID cells.
  • 2N to 1N
homologous pairs
Homologous pairs
  • They associate with each other during prophase 1 through synapsis.
prophase 1
Prophase 1
  • The homologous chromosomes form BIVALENTS. These are replicated homologous chromosomes.
  • The sister chromatids are next to each other, joined at the centromere.
crossing over
Crossing Over
  • Non sister chromatids may cross over during prophase 1 leading to recombinant alleles.
more detail on prophase 1
More detail on Prophase 1

Synapsis-the chromosomes associate

Crossing Over-The Chiasma are the points at which they cross over. A Holliday junction forms when they anneal.

This increases genetic diversity!

metaphase 1
Metaphase 1
  • Bivalents line up at the equator double file.
  • There are many positions that they can align themselves in.
  • This adds to the genetic variation…more on this later!
anaphase 1
Anaphase 1
  • This is where the reduction takes place. The pairs separate, but the sister chromatids remain attached!
telophase 1
Telophase 1
  • The cells are no longer diploid here.
  • The chromosomes may not be exact matches of each other due to crossing over.
prophase ii
Prophase II
  • The nuclei break down again, but the chromosomes do not cross over again.
metaphase ii
Metaphase II
  • Random orientation again contributes to variation in gametes.
anaphase ii
Anaphase II
  • Chromatids are pulled to the opposite poles.
mendel and independent assortment
Mendel and Independent Assortment
  • The presence of an allele of one of the genes in a gamete has no influence over which allele of another gene is present.
  • This is only true for unlinked genes.
  • Click here for a more detailed explanation.
homework 4 2 10 1
HOMEWORK 4.2/10.1
  • Make a T Chart to compare/contrast mitosis and meiosis.
  • Please include as many as possible, but a minimum of 6.
  • You may need to do some research ON YOUR OWN.
  • Due Friday