Chapter 10
Meiosis and Sexual Reproduction
Assignments
Read chapter 10 in textbook
Read corresponding pages in Cliffs AP Test Book
AP Biology
2012-2013
Do questionsMills
1-16
on page
due Nov 7th
Chapter 10
Meiosis and Sexual Reproduction
• Topics
–
–
–
–
–
–
Halving the Chromosome Number
Genetic Recombination
The Phases of Meiosis
Comparison of Meiosis and Mitosis
The Cycle of Life
Changes in Chromosome Number and
Structure
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
• Meiosis
– Form of cell division where the end products are
cells called gametes that have half (haploid) the
normal number (diploid) of chromosomes
– Usually there are male and female gametes
– When male and female gametes come together
in fertilization, a zygote is formed (diploid)
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
• Diploid and Haploid Chromosome Number
– Somatic cells= all cells of body except special cells for
sexual reproduction (eggs and sperm in the case of
humans)
– Humans have 46 (23 pairs) of chromosomes in somatic
cells (23 from mother, 23 from father)
– Homologous chromosomes = similar size, shape and
genetic material (one from mom one from dad)
– Diploid (2n) = cell has all the homologous pairs that that
species is
supposed
to have
(humans
have 22pairs
homologous
Haploid – 0 chromosome
Diploid
– 3 chromosome
pairs
3 chromosomes
6 chromosomes
pairs and one
pair of sex chromosomes)
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
• Mitosis vs Meiosis
Mitosis
Meiosis
Growth and asexual
reproduction
Production of gametes or
spores
Homologous chromosomes
not paired
Homologous chromosomes
paired. Can have crossing
over
One cell division
two identical daughter cells
Two cell divisions
four non identical haploid
daughter cells
Maintains chromosome
number
Halves chromosome number
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
• Steps of Meiosis (Condensed Version)
– Two divisions take place
(after the chromosomes have
duplicated during interphase)
• First - homologous pairs of (duplicated) chromosomes
are divided, one of each pair going to a new cell
(chromosome number is halved)
• Second – sister chromatids are divided, one of each
going to a new cell
• End up with 4 haploid cells
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
Mills AP Biology 2012-2013
Diploid cell (2n) with 4
chromosomes (2 pairs)
Duplicated chromosome #1
from mother pairing with
duplicated chromosome #1
from father
Sister chromatids still attached
Two haploid cells (n)with 2
chromosomes, no pairs
Mills AP Biology 2012-2013
• Meiosis 1
Prophase
1
–chromosomes appear, shorten
and thicken
Dyad
–nuclear membrane disappears
–spindles form
–homologous chromosomes
attracted to each other and
move towards equator
Tetrad
synapsis
= coming together
of homologous chromosomes
to form tetrads
crossing
over can occur
–longest phase
Mills AP Biology 2012-2013
Tetrad
Mills AP Biology 2012-2013
• Meiosis 1

Metaphase 1
Telophase
–tetrads line up at equator
–random arrangement as to
which side maternal or paternal
chromosome is on

Anaphase 1
–cetromeres don’t separate
–homologous chromosomes
separate, but dyads of sister
chromatids stay intact
–tetrads break at crossovers
1
–cell divides in two
–nuclear membrane reappears
–nucleoli reappear
–chromatin reappears
–each cell has haploid number
of chromosomes (still in dyad sister chromatid - state)
–enter interphase like stage =
interkinesis - no DNA replication
–meiosis 2 begins
Mills AP Biology 2012-2013
• Meiosis 2
All stages very similar to mitosis
 Dyads (sister chromatids) separate at
centromere during anaphase 2
 After telophase 2 and cytokinesis, have 4
new cells (gametes) with haploid number of
chromosomes

Mills AP Biology 2012-2013
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
• Meiosis leads to much
genetic variability
– Crossing over during
prophase 1 and the random
alignment of homologous
pairs of chromosomes in
metaphase 1 result in
genetic variability
– Combining gametes from
two genetically dissimilar
parents adds to variability
Mills AP Biology 2012-2013
Meiosis 1 and 2
Review
Click on page for meiosis animation
–What are the advantages
of sexual reproduction?
–What are the
disadvantages of asexual
reproduction?
Meiosis Movie..\..\Biology\Biology Clipart
Movies Animations Sounds\Biology
movies\meiosis_movie.mov
Mills AP Biology 2012-2013
Meiosis Review
Web animation meiosis
http://www.johnkyrk.com/meiosis.html
Meiosis vs mitosis Nova animation
http://www.pbs.org/wgbh/nova/baby/divi_
flash.html
Mills AP Biology 2012-2013
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
• Gametogenesis: Meiosis in Males and Females
– Process by which gametes (haploid egg and sperm
cells) develop in gonads
• Oogenesis – formation of ova in ovaries
• Spermatogenesis – formation of sperm in testes
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
• Oogenesis
– Fetal oogonia (diploid) undergo
mitosis until about 3 mo embryo, then
stop dividing
– All oogonia then develop into primary
oocytes and begin meiosis I, stopping
at prophase I
– At birth all eggs are primary oocytes
with 46 (diploid) chromosomes, each
with two sister chromatids (so actually
96, but still considered diploid)
– (male doesn’t have primary
spermatocytes until puberty)
Mills AP Biology 2012-2013
Occurs in Ovary
Primary oocyte arrested here.
One oocyte each month finishes
meiosis I and progresses
to secondary oocyte
Mills AP Biology 2012-2013
• Oogenesis (cont)
– At puberty, some primary oocytes(diploid) are stimulated
to continue meiosis l each month
– Primary oocyte --> meiosis I (continues) --> secondary
oocyte (haploid - ovum - egg cell) plus a polar body (which
will disintegrate)
• Only eggs destined for ovulation will complete meiosis I
• Meiosis I completes just prior to ovulation (ovulate secondary
oocyte)
• Meiosis ll starts in secondary oocyte after ovulation (in
oviduct)
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
– Secondary oocyte stops
development at metaphase
II
– When secondary oocyte
unites with sperm -->
secondary oocyte continues
meiosis II  large fertilized
egg cell (zygote) plus a tiny
second polar body
– Polar bodies allow cell to
half nuclear contents, but
keep a lot of cytoplasm and
organelles for egg cell
Note to me – see cloning ppt
See NOVA Stem Cell site
Sometimes used in
cloning –
parthenogenesis.
Still diploid
Mills AP Biology 2012-2013
http://www.pbs.org/wgbh/nova/sciencenow/3209/04.html
Secondary oocyte arrested here
Only completes meiosis II
if sperm penetration occurs
Ovulated in this stage
Develops to this stage in oviduct
Primary oocyte arrested here.
One oocyte each month finishes
meiosis I and progresses
to secondary oocyte
Mills AP Biology 2012-2013
Cloning/Nuclear
transfer
Stem Cells
Mills AP Biology 2012-2013
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
• Spermatogenesis
– Occurs in testes
– Immature sex cells (spermatogonia- diploid)) divide
mitotically continually to produce more spermatogonia
– Occurs throughout childhood (how different than
oogenesis?)
– At puberty some spermatogonia develop into primary
spermatocytes secondary spermatocytes spermatids 
mature sperm cells
– Each spermatogonia can produce 4 sperm cells (how
different than oogenesis?)
Mills AP Biology 2012-2013
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
Mills AP Biology 2012-2013
Mills AP Biology 2012-2013
Nice animations of Oogenesis and Spermatogenesis (Martini)
http://wps.aw.com/bc_martini_eap_4/40/10469/2680298.cw/content/index.html
Mills AP Biology 2012-2013
Mills AP Biology 2012-2013
Chapter 10
Meiosis and Sexual Reproduction
Chromosomal Mutations
• Chromosomal Mutations
– Change in chromosome number
– Change in chromosome structure
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Change in Chromosome Number
– Monosomy
– Trisomy
– Polyploidy
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Change in Chromosome Number
– Monosomy
• Individual has only one of a particular pair of
chromosomes
• Usually caused by non disjunction during meiosis
• Usually lethal in animals (unless involves sex
chromosomes)
• Example – Turner Syndrome – only one X
chromosome
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Turner
Syndrome
– Female with only
one X
chromosome
– Short
– Webbed neck
– Can have mental
impairment
– Lack of breast and
ovary development
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Change in Chromosome Number
– Trisomy
• Individual has three copies of a particular chromosome
• Usually caused by non disjunction during meiosis
• Often lethal mutation, but more likely to survive than an
individual with monosmy
• Examples:
– Down Syndrome – extra chromosome #21
– Jacobs Syndrome – extra Y
– Klinefelters Syndrome – extra X
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Trisomy 21
Down
Syndrome
– Extra
chromosome #21
– Mental
retardation
– Characteristic
phenotype
– Can(about 4%)
also be caused by
a 14/21
translocation
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• XYY (Jacobs
syndrome)
– XYY male
– Many normal
– Learning
difficulties
– ? Violent,
antisocial
– May be tall
– Often have acne
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Klinefelters
Syndrome
– XXY male
– Can have more than
2 X’s
– Tall
– Underdeveloped
testicles
– + or – mental
impairment
– Breast development
– Not fertile
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Change in Chromosome Number
– Polyploidy
• Eukaryotic organisms with more than two sets of
chromosomes
– Triploids (3n)
– Tetraploids (4n)
– Pentaploids (5n)
• Not seen in animals – probably lethal
• Very common in plants
– Major evolutionary mechanism
– About 47% of flowering plants are polyploids
– See next slide for examples
» Wheat, cotton, corn, sugarcane, bananas, apples,
watermelon, chrysanthemums, day lilies
Mills Biology 2002
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Change in Chromosome Number
– Polyploidy – How Does it Happen?
• Random mutation that doubles the number of
chromosomes
– Mitosis gone bad producing a germ cell with double
chromosomes
– Gametes formed by mitosis instead of meiosis
– Nondisjunction in meiosis
• When cross two different species, get hybrid
– In animals crossing two species either doesn’t work
or you get a sterile hybrid (Horse x Donkey = Mule)
– In plants, hybrids can reproduce if they become
polyploid
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Polyploidy
– Hybrid sterile unless
double the number of
chromosomes –
chromosomes can’t
form tetrads in meiosis
(no homologous pairs)
– Polyploidy can be
induced in plants with
a chemical called
colchicine
By a
mutation
Haploid
Gamete
12
Mills Biology 2002
+
Haploid
Gamete
15
=
Diploid
27
Polyploidy
Mills Biology 2002
Tetraploid
Showing only
one
chromosome
Diploid
Showing only one
chromosome
Zygote grows
into hybrid
organism and
tries to do
meiosis to form
gametes.
Zygote grows
into hybrid
organism and
tries to do
meiosis to
form gametes.
Can’t pair up
homologous
chromosomes
Can pair up
homologous
chromosomes
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Changes in Chromosome Structure
–
–
–
–
Inversion
Translocation
Deletion
Duplication
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Inversion
– Section of
chromosome inverted
180 o
– Still have same genes,
but the reversed
sequence can lead to
problems
– Does not always cause
a problem
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Translocation
– A segment of one
chromosome moves to
another, non
homologous
chromosome (can
trade places or just
add to other
chromosome)
– Causes about 3-5% of
Down Syndrome
(21/14 translocation)
– Usually serious
consequences
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Deletion
– A piece of the
chromosome is lost –
either from an end or
(by two simultaneous
breaks) the middle.
– Often causes serious
abnormalities
– Example – cri du chat
(Cat Cry Syndrome)
missing short arm of
chromosome #5.
Mills Biology 2002
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
• Duplication
– A segment of the
chromosome is
duplicated more than
once
– End of one homologue
can attach to other
homologue
– Unequal crossing over
can cause
Mills Biology 2002
Chapter 10 Meiosis and Sexual Reproduction
Changes in Chromosome Number and Structure
Which type of gene mutation would you expect to be
more harmful to a protein – one where one nucleotide is
removed or one where three nucleotides are removed?
From Concepts in Genetics by Klug pg 350
• Section Review Question
Mills Biology 200227-1 #5 Explanation
Read
Connecting
the
Concepts
with the
Big Ideas
on pg 189.
WOW!!
!!
Mills AP Biology 2012-2013