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Mitosis and Meiosis
Meiosis Highlights- DNA replication has already occurred prior to the onset of
Meiosis
Meiotic prophase 1
Leptotene
Zygotene (pairing begins)
Pachytene* (homologous pairing complete - recombination begins) - pairing is
intimate
Diplotene - pairing not so intimate
Diakinesis (chromosomes repel - chiasmata visible)
Metaphase 1 - homologous chromosomes pair align on spindle equator
Anaphase 1 - homologous pairs begin to pull apart (chromosomes still have 2
chromatids)
Telophase 1 - pulled apart reaching poles - chromosomes less compacted
Prophase 2 - chromosomes condense
Metaphase 2 - align on spindle
Anaphase 2 - chromatids of each chromosome pull to opposite poles
Telophase 2 - reach poles, de-condense, nuclear envelope forms
Cytokinesis leaving 4 haploid gametes (usually) - depending on the species
1
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2
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Aa can be subdivided into A and
a
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Normally at the end of meiosis you get 4 nuclei but only one of them becomes an
egg and the others are involved in double fertilization in the productive industry
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Recombination is similar to crossing over of chromatids
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Mitosis- generating somatic cells
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No eukaryotic organism that has just one pair of chromatids
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In meiosis the first thing that happens is dna replication where each chromosome
is composed of chromatids
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Meiosis results in 4 daughter cells
Refer to figure 2-16a
• Pachytene spread- viewing it with electron microscopy with the tungsten stain
• Synaptonemal complex- has proteins in it
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Meiosis in fungi such as Neurospora crassa
• Most of the time they live as haploids
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After the second meiotic division, 4
products are formed
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Get the exact
same mendelion ratio
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2 different mating types
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Fuse and undergo meiosis
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This was perhaps the first
method used to follow DNA segregation directly
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CAPS - cleaved amplified polymorphisms
RAPDS- random amplified polymorphic DNA
AFLP- amplified fragment length polymorphisms
SSCP- single stranded conformational polymorphism
SNP’s - single nucleotide polymorphism [follow a single nucleotide change]
Restriction fragment length polymorphisms [Refer to slides posted]

• An allele is a stretch of DNA that encodes a gene
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double stranded DNA molecule and along the sequence three E’S are
present
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• Allele a
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Sequence is missing and is different at that particular location
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This
cutting of sequences liberates fragments
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Don’t need the whole gene, just need different fragments
that can distinguish between genes
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• Run gel electrophoresis on an agarose gel
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Separates DNA by size of the DNA
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• Can see the bands of stained with ethidium bromide
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Once the gel is run want to apply a probe to detect gene of
interest but first transfer DNA to nylon membrane which is the exact image of the
gel
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Then take the probe [stretch of DNA
which is homologous to the strands I’m interested in]
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Put an X-ray film on it
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• See different banding patterns —> Size of DNA is known
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