Download Meiosis - My Haiku

Cell Division: Meiosis
Ch 11-4; p. 275-278
Types of Reproduction
Asexual – mitosis; results
in clones or genetically
identical offspring (2N)
Sexual – meiosis; results
in offspring genetically
different from parent
(N)
Easy
Mitosis
Genetic variety;
Adaptability
Meiosis
Genetically
Identical
Energy;
Must have mate
Vocabulary
Haploid – 1 copy of each
chromosome (N)
Diploid – 2 copies of each
chromosome (2N)
Homologous Chromosomes –
paired like chromosomes
Haploid vs. Diploid
Humans have a diploid (2N)
number of 46.
What is the haploid (N)
number?
Fruit flies have a haploid (N)
number of 4.
What is the diploid (2N)
number?
Meiosis
Double Mitosis
Two divisions (same steps)
Reduction Division
Chromosome number is reduced by
half
Diploid to haploid
Sexual Reproduction
Produces 4 genetically UNIQUE
cells
Stages of Meiosis
Interphase I
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I
Duplicated homologous chromosomes
are separated into two daughter cells.
Chromosome number cut in half
(HAPLOID).
Each cell receives one homologue of
each pair of chromosomes.
Crossing over may occur; so cells are
genetically DIFFERENT.
Sister chromatids DO NOT separate.
Quick Questions: Interphase
What do the chromosomes look like in
interphase I?
What important event occurs during
this stage?
Stages of Meiosis
Prophase I
Chromosomes thicken
and condense
Nuclear membrane
disintegrates
Spindle fibers form
Homologous
chromosomes pair.
(Tetrad)
Crossing over occurs.
Stages of Meiosis
Prophase I:
Homologous Pairs
MATERNAL and
PATERNAL
chromosomes find
each other and
pair
TETRAD forms =
4 sister
chromatids
Stages of Meiosis
Prophase I:
Crossing Over
Crossing Over occur
as chromatids in
tetrad exchange parts
Genetic
recombination – new
combination of alleles
(form of gene) on
chromosome
Quick Questions
What event makes crossing over
possible?
What is a tetrad?
Stages of Meiosis
Metaphase I
Homologous pairs
of chromosomes
line up at equator
(mitosis is not pairs)
Spindle fibers
attach centromere
Quick Question
Where are the chromosomes in
metaphase I?
Stages of Meiosis
Anaphase I
TETRADS
separate
Each chromosome
still contains two
chromatids
(mitosis has sister
chromatids split)
Quick Question
What happens to each homologous
pair of chromosomes during anaphase
I?
Stages of Meiosis
Telophase I
Spindles
disappear
Two clusters of
chromosomes
Only one of
homologous pair,
therefore,
Diploid
Quick Question
How many cells are formed at the end
of telophase I?
Each chromosomes consists of how
many chromatids or strands?
Describe the genetic composition of
the cells formed by meiosis I.
Stages of Meiosis
Interphase I
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II
What stage of cell division is missing? Look
back at first few slides.
No Interphase
Without
interphase,
what
important
event does
not occur?
No Replication of
Chromosomes
Meiosis II
Sister chromatids are
separated
Resembles mitosis
Four cells are produced, they
are:
Haploid
Genetically different
Stages of Meiosis (cont.)
Prophase II
Chromosomes
recondense if
necessary
Spindle fibers
reform
Do chromosomes pair up?
Prophase II
Stages of Meiosis (cont.)
Metaphase II
Chromosomes
line up along
equator
Spindle fibers
have attached
to sister
chromatids
Describe the position of the chromosomes.
Stages of Meiosis (cont.)
Anaphase II
Sister
chromatids
separate and
move to
opposite poles
Anaphase II
Stages of Meiosis (cont.)
Telophase II
Sister chromatids
uncoil
Nuclear membrane
reforms
4 GENETICALLY
DIFFERENT
HAPLOID CELLS
(mitosis is 2 identical
diploid cells)
Telophase II
Quick Question
How many cells are formed at the end
of telophase II?
Compare the number of chromosomes
in the newly formed cells to the
number in interphase I.
Meiosis Movie
Web Sites
http://www.erin.utoronto.ca/~w3bio3
80/Lectsked/Supple2/meiosis.html
(meiosis graphics)
Comparison Graphics
Meiosis
vs.
4 cells
2 divisions
Sexual
Haploid
Only in sex cells
Chromosomes
replicate and pair
Shuffling of genes
produce cells that
are genetically
different than parent
Mitosis
2 cells
1 division
Asexual
Diploid
Occurs all over
Chromosomes
replicate;DON’T pair
All generations
maintain exact
genetic identity of
parent.
Vocabulary
Haploid
Diploid
Homologous Chromosomes
Crossing over
Errors in Meiosis
Nondisjunction – extra copies
or missing copies of
chromosomes when
homologous pairs or sister
chromatids DO NOT separate
Quick Question
How do errors here compare
with errors in mitosis?
Why Sex?
What are the
advantages of sexual
reproduction?
Asexual reproduction takes less
energy – more offspring, quickly
without variation. Why change what
works?
Genetically different offspring may
be more successful.
Gametogenesis
Formation of sex cells
(GAMETES)
Spermatogenesis
Oogenesis
Sperm – haploid (N) male gamete (sex cell)
Egg – haploid (N) female gamete (sex cell)
Zygote – diploid (2N) fertilized egg
Veeerrry Interesting…
Sperm begins meiosis at end of
gestation. Arrested at prophase
I. When does it restart?
At 5 months of gestation ovary
contains 6-7 million oogonia.
Production at birth, and by
puberty this is reduced to only
300,000-400,000.
More interesting ideas…
Meiosis I in females completes during
preparation for ovulation
Unequal division
WHY?
Polar body – contains haploid set of
chromosomes; discarded nucleus.
Stops at metaphase II
Oogenesis in Ovary
Oocyte (egg) – Completes
meiosis II only at fertilization.
If female has 2 kids how many
times has she completed meiosis?
Remember that ¾ fertilizations
are lost
Emry
ology
links
http://imcip.gsm.com/scripts/login.asp?u=http://imcip.gsm.com/integrated/