11/12/2012
We are going to the lab
BRIEFLY today before our
QUIZ. You will be in groups
of four so begin to plan who
you want to work with. Be
ready to get started as soon
as the bell rings.
11/12/2012
Pick up notes
and glue
them onto
the next
available
pages that
face each
other.
11/13/2012
Take out your notes
from yesterday and
be in your seat
before the bell rings.
How are sperm and egg made?
46
23
46
23
92
46
Homologous Chromosomes
 In the body cells (somatic cells) of animals
and most plants, chromosomes occur in pairs.
 A cell with two of each kind of chromosome is
called a diploid cell or 2n.
 Organisms produce gametes or sex cells that
contain one of each type of chromosome. These
gametes are called haploid cells or n.
(N represents the number of chromosomes found in each cell.)
Chromosome numbers
Do all organisms have the same number of chromosomes?
Homologous Chromosomes
The two chromosomes of each pair in a
diploid cell are called homologous
chromosomes.
Homologous Chromosomes
How many autosomes are found in the human body cell?
Match up the homologous chromosomes
Meiosis
Meiosis is a two-part cell division process,
which results in gametes with one half the
number of chromosomes of the parent
cell.
produces four daughter cells
all daughter cells are haploid
chromosomes are shuffled in the process, so
that each daughter cell has a unique
combination (crossing over)
http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meiosis.html
Meiosis creates
4 haploid cells
Spermatogenesis (meiosis
of sperms cells) takes about
64 days. All 4 sperm will
survive.
Oogenesis (meiosis of egg
cells) is complete when a
female is born. Only 1 egg
of the 4 will become viable.
Meiosis I
Stage
Events
Interphase I
Chromosomes
replicate
In nucleus
Photo
Meiosis I
Stage
Events
Interphase I
Chromosomes
replicate
Prophase I
Chromosomes
become visible
Photo
Meiosis I
Stage
Events
Photo
Interphase I
Chromosomes replicate
Prophase I
Chromosomes become
visible
Metaphase I
Sister chromatids
form tetrads at the
equator
Independent
assortment occurs
= pair of homologous
chromosomes
Crossing Over
To make things
interesting crossing
over can occur.
During Metaphase I,
the homologous
chromosomes line up
together and form
tetrads.
Crossing Over
Crossing over: two
chromosomes break and
reattach to the
opposite end piece.
Crossing over increases
the number of
variations that can exist
in offspring.
Crossing Over
Which of the following did crossing over
ONLY take place?
Independent assortment occurs – chromosomes separate
randomly causing GENETIC RECOMBINATION
OR
Homologs line up at equator or metaphase
plate
22
Meiosis I
Stage
Events
Interphase I
Chromosomes
replicate
Prophase I
Chromosomes
become visible
Metaphase I
Sister chromatids
form tetrads at the
equator
Anaphase I
Homologous
chromosomes move
AWAY to the poles
Photo
Meiosis I
Stage
Events
Interphase I
Chromosomes
replicate
Prophase I
Chromosomes
become visible
Metaphase I
Sister chromatids
form tetrads at the
equator
Anaphase I
Homologous
chromosomes move
AWAY to the poles
Telophase I
2 new cells
Photo
Meiosis II
Stage
Events
Photo
Interkinesis
Nuclear membrane forms
No replication of chromosomes
No Picture
Meiosis II
Stage
Events
Photo
Interkinesis
Nuclear membrane forms
No replication of chromosomes
No Picture
Prophase II
Spindle forms
Nucleus & nucleolus disappear
Chromosomes condense
Meiosis II
Stage
Events
Photo
Interkinesis
Nuclear membrane forms
No replication of chromosomes
No Picture
Prophase II
Spindle forms
Metaphase II
Chromosomes align at the
equator, not homologs
equator
NOW …
single file line
Meiosis II
Stage
Events
Photo
Interkinesis
Nuclear membrane forms
No replication of chromosomes
No Picture
Prophase II
Spindle forms
Metaphase II
Chromosomes align at the
equator
Anaphase II
Sister chromatids separate
Meiosis II
Stage
Events
Photo
Interkinesis
Nuclear membrane forms
No replication of chromosomes
No Picture
Prophase II
Spindle Forms
Metaphase II
Chromosomes align at the
equator
Anaphase II
Sister chromatids separate
Telophase II
4 genetically different cells
with ½ the number of
chromosomes
Meiosis – one more time
Meiosis is a two-part cell division process….
Meiosis II – one more time
4
… which results in gametes with one
half the number of chromosomes of the
parent cell.
Mitosis vs. MEIOSIS
mitosis
•Creates somatic cells
•2 cells
•diploid cells
•46 chromosomes
•Daughter cells are identical to
parent cell
•1 division
•Homologous chromosomes line up
in a single file line in metaphase
meiosis
•Creates gametes
•4 cells
•haploid cells
•23 chromosomes
•Daughter cells are NOT identical
to parent cells
•2 divisions
•Homologous chromosomes line
up in a single file line in
metaphase II
•Chromosomes duplicate in Interphase
•Both a type of cell division
•Both required to sustain life
http://www.pbs.org/wgbh/nova/miracle/divi_flash.html