Meiosis Notes
Gametes are the reproductive cells (sperm and egg), and each
contains half the number of chromosomes found in other cells.
They fuse by the process of fertilization to create a zygote.
How many chromosomes are in a human cell? 46
How many chromosomes are in a sperm? Egg? 23
Diploid = normal number of chromosomes
Meaning that they have two copies of each chromosomes
Haploid = half the number of chromosomes.  made by meiosis
1
Meiosis Notes
Meiosis makes the gametes that combine to make “Me and I.”
1. DNA is copied (replicated) once
2. Cell divides twice (P.M.A.T. 1 and 2)
The end results of meiosis are 4 non-identical gametes with half the
normal number of chromosomes.
Meiosis I is the first division.
In this stage paired homologous chromosomes (example: X
and Y) “cross over” causing in increase in genetic diversity
and are separated into cells
Basically, meiosis I separates the two homologous
chromosomes.

Prophase I = cell Prepares to divide:
o Chromatin condenses into
tetrads = homologous pairs of
doubled chromosomes,
Qui ckTime™ and a
decompressor
are needed to see thi s pi cture.
o Nuclear membrane disappears.
Crossing over occurs during this stage.

Metaphase I = homologous
chromosomes (tetrads) line up in Middle.

Qui ckTime™ and a
decompressor
are needed to see thi s pi cture.
Anaphase I = tetrads split, doubled
chromosomes move Away to opposite
Quic k Ti me™ and a
dec ompres s or
are needed to s ee t his pic t ure.
poles.
2
Meiosis Notes

Telophase I = cell "Tears" in two,
cytokinesis (cytoplasmic division) leads to 2
QuickT ime ™an d a
deco mpre ssor
ar e need ed to see this pictur e.
non-identical haploid cells.
Meiosis II is the second division.
In this stage the doubled chromosomes are divided into 4
non-identical daughter cells.
Basically, meiosis II separates the two sister chromatids
of each chromosome

Prophase II= cell Prepares to divide,
haploid # of doubled chromosomes, no
QuickT ime ™an d a
deco mpre ssor
ar e need ed to see this pictur e.
nuclear membrane present

Metaphase II = doubled chromosomes
Quick Time™a nd a
dec ompr esso r
ar e nee ded to see this pictur e.
line up in Middle.
3
Meiosis Notes

Anaphase II = Sister chromatids (now
called chromosomes), move Away to
Quic kT i me™ and a
dec om pres s or
are needed t o s ee thi s pi c ture.
opposite poles.

Telophase II = cell "Tears" in two,
nuclear membrane reforms,
chromosomes disperse into chromatin,
QuickTi me™ and a
decompressor
are needed to see thi s pi ctur e.
cytokinesis (cytoplasmic division)
leads to 4 non-identical haploid
gametes.
Meiosis results in 4 non-identical daughter cells
QuickTi me™ and a
decompressor
are needed to see thi s pi ctur e.
4
Meiosis Notes
Meiosis and mitosis have much in common. However, meiosis has
two unique features.

Synapsis
o
Homologous chromosomes pair all along
their lengths in meiosis I
o

Cross over
Reduction division
o
There is no chromosome duplication between
the two meiotic divisions
o
Produces haploid gametes
5
Meiosis Notes
6