Cellular Division to Produce Gametes
Take out all of your cells. See if you can
arrange them in the correct order. Here are
some hints:
• There will be 2 cellular divisions(PMAT)
•As cells divide they get smaller
Which cell would you begin with?
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MEIOSIS: cell division to
produce the reproductive
cells or GAMETES
Occurs only in organisms that
reproduce sexually
Occurs in 2 stages:
MEIOSIS I: Results in 2 cells
with a reduction by half the total
number of chromosomes
MEIOSIS II: Results in 4 cells
with a division of the chromatids
Tetrads are separated
A germ cell forms in testes or ovaries
It has the total # of chromosomes
referred to as a DIPLOID(2n) cell
PI
HOMOLOGOUS chromosomes
pair forming a TETRAD(4 chromatids)
Tetrads are aligned
CROSSING OVER occurs and ends
of chromosomes are exchanged
resulting in new gene combinations
MI
AI
Crossing over is one of
several random processes that
increase variation in offspring
TI
 Half of your
chromosomes come
from one parent and
half from the other
 In independent
assortment these
maternal and paternal
chromosomes are
aligned randomly in
the tetrad during
metaphase I
 When chromatids are separated in metaphase II, only 1
of the two ends up in each gamete
 This too is a random process
Oogenesis and Spermatogenesis
SPERMATOGENESIS
OOGENESIS
Please label the sections below
the fold and draw these diagrams
Not too small! Fill the space.
MEIOSIS I
MEIOSIS I
MEIOSIS II
MEIOSIS II
NO G1 or S
Two of Mendel’s Laws
occur during meiosis:
Law of Independent
Assortment: homologous
chromosomes are
aligned randomly
during Metaphase I
Centrioles divide
and reform a new
meiotic spindle
The 2 cells that result
from meiosis I have
half the chromosomes
as the germ cell and are
HAPLOID(n)
PII
MII
Law of Segregation
Only 1 of 2
chromosomes
ends up in
each gamete
Chromatids are now
separated
AII
4 haploid cells result from meiosis II
TII
SPERMATOGENESIS
OOGENESIS
Now using the two colors you used
for crossing over, draw in the
chromosomes
Division of the cytoplasm
is equal. All cells same size.
Meiosis to produce
the male gametes:
spermatozoa(sperm)
MEIOSIS I
MEIOSIS II
MEIOSIS II
Following meiosis a flagella and an enzyme cap are formed
on each of the 4 viable spermatozoa
Meiosis to produce
the female gametes:
ovum(egg)
Division of the cytoplasm
is unequal and which cell
receives the most is random.
MEIOSIS I
The larger cell will become the
ovum the smaller cell
is called a polar body
and is non viable.
POLAR BODIES
MEIOSIS II
MEIOSIS II
A polar body’s purpose is to hold
chromosomes, they are not viable.
OVUM
The result of oogenesis is 1 viable ovum
and 3 nonviable polar bodies